Search

The habitat quality of urban forest patches is determined by the composition and structure of vegetation which in turn affects the quality of trophic resources and shelter provided for wildlife species. In addition, urban development in the landscape surrounding forest patches can affect species' movement between patches, further influencing habitat quality. Understanding how species respond to variation in habitat quality among urban forest patches is especially important for species that contribute to ecosystem services and disservices for urban residents. Here, we assessed habitat quality provided by urban forest patches for white‐footed mice (Peromyscus leucopus) because they are one of the key reservoir species for Lyme disease and they influence disease dilution ecosystem services provided by mammal communities. We examined variation in vegetation composition and structure in forest patches across a gradient of landscape‐scale urban development in and around Philadelphia, PA, USA. In particular, we focused on shifts in vegetation composition and structure associated with invasive understory shrubs given their prevalence in our study system. We then quantified the numerical (index of relative abundance) and morphological responses of white‐footed mice to variation in habitat quality. While we observed no significant effects of environmental variables on our index of mouse relative abundance in forest patches, environmental variables associated with vegetation structure and composition were associated with shifts in mouse morphology. Most notably, mice were larger at sites with more invasive shrub species. This indicates that invasive understory shrubs may be creating higher‐quality habitat for white‐footed mice. Because larger‐bodied mice are likely to feed more ticks, this result has significant implications for Lyme disease dynamics in urban areas, such as amplified transmission. [ABSTRACT FROM AUTHOR]

Functional response is the crucial factor in understanding the efficiency of coccinellid predators in managing the sucking insect pest species. The six-spotted ladybird beetle, Cheilomenes sexmaculata, is known to show a voracious appetite for prey species such as the whitefly, Bemisia tabaci, the papaya mealybug, Paracoccus marginatus, the cotton aphid, Aphis gossypii and the cotton mealybug, Phenacoccus solenopsis, which are devastating sucking pests of cotton. An experiment was conducted to understand the functional response of C. sexmaculata against mixed prey densities by using all four species as prey. Results showed that all the developmental stages of the predator displayed a type-II functional response. The first instar had the highest attack rate (à) according to Roger’s random equation and Holling’s disc Eq. (1.27 ± 0.12) and (0.82 ± 0.06), followed by the fourth instar grub (1.01 ± 0.05) and (0.67 ± 0.02), respectively. Using both equations, male and female, the third and fourth instar grubs had the lowest handling time (Th) (0.01 ± 0.00). Therefore, it can be suggested that the third and fourth instar grubs and adults of both sexes of C. sexmaculata could be employed for augmentative biological pest control programmes of this sucking pest complex in the cotton crop ecosystem as a sustainable pest management strategy. [ABSTRACT FROM AUTHOR]

We investigated the food-dependent growth and thermal response of the freshwater ciliate Colpidium kleini using numerical response (NR) experiments. This bacterivorous ciliate occurs in lotic water and the pelagial of lakes and ponds. The C. kleini strain used in this work was isolated from a small alpine lake and identified by combining detailed morphological inspections with molecular phylogeny. Specific growth rates (rmax) were measured from 5 to 21 °C. The ciliate did not survive at 22 °C. The threshold bacterial food levels (0.3 − 2.2 × 106 bacterial cells mL−1) matched the bacterial abundance in the alpine lake from which C. kleini was isolated. The food threshold was notably lower than previously reported for C. kleini and two other Colpidium species. The threshold was similar to levels reported for oligotrich and choreotrich ciliates if expressed in terms of bacterial biomass (0.05 − 0.43 mg C L−1). From the NR results, we calculated physiological mortality rates at zero food concentration. The mean mortality (0.55 ± 0.17 d−1) of C. kleini was close to the mean estimate obtained for other planktonic ciliates that do not encyst. We used the data obtained by the NR experiments to fit a thermal performance curve (TPC). The TPC yielded a temperature optimum at 17.3 °C for C. kleini, a maximum upper thermal tolerance limit of 21.9 °C, and a thermal safety margin of 4.6 °C. We demonstrated that combining NR with TPC analysis is a powerful tool to predict better a species' fitness in response to temperature and food. [ABSTRACT FROM AUTHOR]

Abstract Using a recursion model with real parameters of Nabis pseudoferus, we show that its filial cannibalism is an optimal foraging strategy for life reproductive success, but it is not an evolutionarily optimal foraging strategy, since it cannot maximize the descendant’s number at the end of the reproductive season. Cannibalism is evolutionarily rational, when the number of newborn offspring produced from the cannibalized offspring can compensate the following two effects: (a) The cannibalistic lineage wastes time, since the individuals hatched from eggs produced by cannibalism start to reproduce later. (b) Cannibalism eliminates not only one offspring, but also all potential descendants from the cannibalized offspring during the rest of reproductive season. In our laboratory trials, from conspecific prey Nabis pseudoferus did not produce newborn nymphs enough to compensate the above two effects.

BACKGROUND: Biological control with predatory mites is applied against pests in greenhouse crops. Chemical control with the use of selective, reduced‐risk pesticides, is an important component of Integrated Pest Management (IPM) programs, that often needs to be combined with biological control. Here, we evaluated the effect of plant pollen when used as supplementary food on the survival, reproduction and predation of the predatory mite Amblydromalus limonicus (Acari: Phytoseiidae) after exposing young larvae and adults to flonicamid, an insecticide of moderate toxicity to phytoseiids. Pollen is an important alternative food for generalist phytoseiids ensuring survival and supporting populations build‐up during periods of prey scarcity. Two regimes of cattail (Typha angustifolia L.) pollen differing in application frequency were used. In the first, the total amount of pollen was supplied once, within 30 min after insecticide application, whereas in the second regime, the same amount of pollen was supplied gradually, i.e., every 48 h. RESULTS: Regardless of the frequency of application, pollen provisioning results in a reduction in prey (thrips) consumption relative to the control (no pollen provisioning). Nevertheless, when adult mites were directly exposed to flonicamid residues, pollen provisioning attenuated the reduction in prey consumption as compared to the control. In addition, the gradual (every 48 h) provisioning of pollen to adult predators exposed to flonicamid residues impacted positively the intrinsic rate of population increase (rm) of A. limonicus as compared to when feeding on prey. CONCLUSION: Our results reveal an unexpected role of pollen provisioning in alleviating pesticides side‐effects on phytoseiids. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Using a recursion model with real parameters of Nabis pseudoferus, we show that its filial cannibalism is an optimal foraging strategy for life reproductive success, but it is not an evolutionarily optimal foraging strategy, since it cannot maximize the descendant's number at the end of the reproductive season. Cannibalism is evolutionarily rational, when the number of newborn offspring produced from the cannibalized offspring can compensate the following two effects: (a) The cannibalistic lineage wastes time, since the individuals hatched from eggs produced by cannibalism start to reproduce later. (b) Cannibalism eliminates not only one offspring, but also all potential descendants from the cannibalized offspring during the rest of reproductive season. In our laboratory trials, from conspecific prey Nabis pseudoferus did not produce newborn nymphs enough to compensate the above two effects. [ABSTRACT FROM AUTHOR]

The dynamic interactions between predators and their prey have two fundamental processes: numerical and functional responses. Numerical response is defined as predator growth rate as a function of prey density or both prey and predator densities [dP/dt = f(N, P)]. Functional response is defined as the kill rate by an individual predator being a function of prey density or prey and predator densities combined. Although there are relatively many studies on the functional response in mammalian predators, the numerical response remains poorly documented. We studied the numerical response of Eurasian lynx (Lynx lynx) to various densities of its primary prey species, roe deer (Capreolus capreolus), and to itself (lynx). We exploited an unusual natural situation, spanning three decades where lynx, after a period of absence in central and southern Sweden, during which roe deer populations had grown to high densities, subsequently recolonized region after region, from north to south. We divided the study area into seven regions, with increasing productivity from north to south. We found strong effects of both roe deer density and lynx density on lynx numerical response. Thus, both resources and intraspecific competition for these resources are important to understanding the lynx population dynamic. We built a series of deterministic lynx–roe deer models, and applied them to the seven regions. We found a very good fit between these Lotka–Volterra type models and the data. The deterministic models produced almost cyclic dynamics or dampened cycles in five of the seven regions. Thus, we documented population cycles in this large predator–large herbivore system, which is rarely done. The amplitudes in the dampened cycles decreased toward the south. Thus, the dynamics between lynx and roe deer became more stable with increasing carrying capacity for roe deer, which is related to higher productivity in the environment. This increased stability could be explained by variation in predation risk, where human presence can act as prey refugia, and by a more diverse prey guild that will weaken the direct interaction between lynx and roe deer. [ABSTRACT FROM AUTHOR]

Indirect interactions are widespread among prey species that share a common predator, but the underlying mechanisms driving these interactions are often unclear, and our ability to predict their outcome is limited.Changes in behavioural traits that impact predator space use could be a key proximal mechanism mediating indirect interactions, but there is little empirical evidence of the causes and consequences of such behavioural‐numerical response in multispecies systems.Here, we investigate the complex ecological relationships between seven prey species sharing a common predator. We used a path analysis approach on a comprehensive 9‐year data set simultaneously tracking predator space use, prey densities and prey mortality rate on key species of a simplified Arctic food web.We show that high availability of a clumped and spatially predictable prey (goose eggs) leads to a twofold reduction in predator (arctic fox) home range size, which increases local predator density and strongly decreases nest survival of an incidental prey (American golden plover). On the contrary, a scattered cyclic prey with potentially lower spatial predictability (lemming) had a weaker effect on fox space use and an overall positive impact on the survival of incidental prey.These contrasting effects underline the importance of studying behavioural responses of predators in multiprey systems and to explicitly integrate behavioural‐numerical responses in multispecies predator–prey models. [ABSTRACT FROM AUTHOR]

Context: Chital deer (Axis axis) are long established in the northern Queensland dry tropics, and at high densities are considered pests by cattle graziers. Cost-effective management is difficult for widespread, fluctuating populations of vertebrate pests such as these deer. Historically, control of chital deer has been limited to recreational and some commercial ground-shooting and trapping. Concerns over chital deer impacts were heightened during drought in 2015 and funding became available for aerial culling. Aim: This study set out to determine (1) distribution and abundance, (2) seasonal reproductive output, (3) potential and actual rates of increase and their determinants, and (4) efficient management strategies for chital deer in the northern Queensland dry tropics. Methods: In 2014, ~13 000 km2 of the main distribution was surveyed by helicopter. Multiple vehicle ground surveys per year monitored chital deer density on two properties during 2013–2022. Seasonal shot samples of deer on both properties assessed reproductive output during 2014–2016. Aerial surveys during 2016–2020 determined chital deer densities on seven properties, prior to aerial culling on four properties. Finally, the maximum rate of increase of chital deer was calculated from life-history data. Key results: Regionally, chital deer are patchily distributed and so are best monitored locally where densities can be >50 deer km−2. Vehicle ground surveys recorded an ~80% decline in chital deer populations on two properties over 7–10 months during drought in early 2015, with a similar rate being recorded by aerial survey at a third site. There was little recruitment during the drought, but the decline was seemingly driven by adult mortality. Aerial shooting further reduced populations by 39–88% to <3 deer km−2 on four properties. Where there was no continuing control, culled populations recovered to pre-cull densities or higher after 2.4 years. One unculled property recovered to its pre-drought density after 6 years. Rates of recovery were at or higher than the maximum annual rate of increase for chital deer estimated here as 26–41%. Conclusions: Drought has a lasting effect on this chital deer population, because of the resulting large population decline and the modest rate of any recovery in the absence of culling. Culling can reduce populations to low density, but the removal rate needs to be sustained to suppress future growth. Implications: Drought provides a strategic opportunity to further reduce chital deer populations for enduring control. Large reductions are feasible given the clumped dispersion of populations within properties and in the region. Chital deer at high densities are considered pests by northern Queensland cattle graziers, but control can be costly. Populations of chital declined by ~80% during drought, providing an opportunity to hold populations at low density through culling. Aerial shooting further reduced populations, but some populations recovered to pre-drought densities after ~6 years when there was no further control. Photograph by J. Scanlan. [ABSTRACT FROM AUTHOR]

The strength of indirect biotic interactions is difficult to quantify in the wild and can alter community composition. To investigate whether the presence of a prey species affects the population growth rate of another prey species, we quantified predator-mediated interaction strength using a multi-prey mechanistic model of predation and a population matrix model. Models were parametrized using behavioural, demographic and experimental data from a vertebrate community that includes the arctic fox (Vulpes lagopus), a predator feeding on lemmings and eggs of various species such as sandpipers and geese. We show that the positive effects of the goose colony on sandpiper nesting success (due to reduction of search time for sandpiper nests) were outweighed by the negative effect of an increase in fox density. The fox numerical response was driven by changes in home range size. As a result, the net interaction from the presence of geese was negative and could lead to local exclusion of sandpipers. Our study provides a rare empirically based model that integrates mechanistic multi-species functional responses and behavioural processes underlying the predator numerical response. This is an important step forward in our ability to quantify the consequences of predation for community structure and dynamics. [ABSTRACT FROM AUTHOR]

In recent years, Dactylopius opuntiae (Cockerell) (Hemiptera: Dactylopiidae) has become an increasing threat to the cultivation of prickly pear crops in Morocco. To control this harmful insect scale pest, biological control is usually accompanied by chemical control applications. In this context, the use of some insecticides can alter the numerical response of beneficial organisms (predators) associated with this cochineal. In this study, we investigated the effect of the residues of some insecticides «(d-limonene (60 g/L) applied at 100 mL/hL, mineral oil (780 g/L) at 2000 mL/hL, potassium salts of fatty acid (500 g/L) at 40 mL/hL, pyriproxyfen (100 g/L) at 25 mL/hL, and potassium salts of fatty acid (C7-C18) (500 g/L) at 300 mL/hL)» on the numerical response of Cryptolameus montrouzieri (Mulsant) (Coleoptera: Coccinellidae) feeding on D. opuntiae females under laboratory conditions. The sublethal concentration residues of all tested insecticides did not have lethal effects on Cryptolaemus montrouzieri females. D-limonene (Efficiency of Conversion of Ingested food (E.C.I) = 1371.85), mineral oil (E.C.I = 1383.06), potassium salts of fatty acid (E.C.I = 1583.24), and pyriproxyfen (E.C.I = 987.13) were the most compatible with the predator C. montrouzieri, as they did not significantly affect the number of eggs laid by the females compared to the untreated control. Potassium salt of fatty acid (C7–C18) (500 g/L) (E.C.I = 905.93) was the least compatible with C. montrouzieri, as it led to a significant reduction in the number of eggs laid by predatory females. [ABSTRACT FROM AUTHOR]

Population dynamics of aquatic ciliates are controlled "bottom‐up" via food supply and "top‐down" by grazing and parasitism. While intrinsic growth rates of ciliates under saturating food conditions have been studied in some detail, mortality rates induced by starvation have received little attention thus far. To this end, we examined the response of three algivorous freshwater ciliate species to starvation using three different optical methods. Two of these methods, i.e. ciliate mortality rates (δ) estimated from (i) numerical response experiments and (ii) the rate of decline (ROD) in cell numbers, investigated the response of the ciliate population using conventional light microscopy. The third method, imaging cytometry using a FlowCAM instrument, monitored single cells during the starvation experiment. Like light microscopy, the FlowCAM approach estimated δ based on ROD in the experimental containers. However, imaging cytometry also measured the relative cellular chlorophyll a content in the ciliates' food vacuoles as a proxy for the nutritional status of the cells. The linear decline of the cellular chl. a yielded an independent estimate of δ that was similar to δ calculated from ROD. Additionally, the FlowCAM measurements revealed a high degree of phenotypic plasticity of the ciliates when exposed to starvation. [ABSTRACT FROM AUTHOR]

Increases in consumer abundance following a resource pulse can be driven by diet shifts, aggregation, and reproductive responses, with combined responses expected to result in faster response times and larger numerical increases. Previous work in plots on large Bahamian islands has shown that lizards (Anolis sagrei) increased in abundance following pulses of seaweed deposition, which provide additional prey (i.e., seaweed detritivores). Numerical responses were associated with rapid diet shifts and aggregation, followed by increased reproduction. These dynamics are likely different on isolated small islands, where lizards cannot readily immigrate or emigrate. To test this, we manipulated the frequency and magnitude of seaweed resource pulses on whole small islands and in plots within large islands, and we monitored lizard diet and numerical responses over 4 years. We found that seaweed addition caused persistent increases in lizard abundance on small islands regardless of pulse frequency or magnitude. Increased abundance may have occurred because the initial pulse facilitated population establishment, possibly via enhanced overwinter survival. In contrast with a previous experiment, we did not detect numerical responses in plots on large islands, despite lizards consuming more marine resources in subsidized plots. This lack of a numerical response may be due to rapid aggregation followed by disaggregation or to stronger suppression of A. sagrei by their predators on the large islands in this study. Our results highlight the importance of habitat connectivity in governing ecological responses to resource pulses and suggest that disaggregation and changes in survivorship may be underappreciated drivers of pulse-associated dynamics.

The olive fruit fly, Bactrocera oleae, is one of the main pests of this crop and its control requires the development of methods environmentally safer than those used mostly nowadays, being biological control a possible alternative. Accordingly, the capacity of parasitisation and the biological parameters of Muscidifurax raptorellus, a generalist parasitoid of dipteran pupae, were evaluated on B. oleae at 25°C, 80% RH and a 16:08 h light/dark photoperiod. In a development assay, the rates of parasitism ranged 60% to 72% and the duration of the preimaginal period was between 17.0 and 18.5 days. The total mean number of adult wasps produced per pair in a reproduction assay was 50.7, with a mean daily production of 7 individuals and a mean rate of parasitism of 32.6%. The moment of maximum offspring production was estimated at 2.6 days after the beginning of the oviposition. The intrinsic rate of natural increase of M. raptorellus on B. oleae was 0.147, what determines a population doubling time of 4.7 days. The functional response was type II and the maximum attack rate in 24 h was 19.6 pupae. At host densities ranging 20–80 pupae per female, the number of adult wasps produced was around 20–22. The results obtained show the potential of M. raptorellus to be used for the biological control of B. oleae. [ABSTRACT FROM AUTHOR]

Most prominent theories of food web dynamics imply the simultaneous action of bottom-up and top-down forces. However, transient bottom-up effects resulting from resource pulses can lead to sequential shifts in the strength of top-down predator effects. We used a large-scale field experiment (32 small islands sampled over 5 years) to probe how the frequency and magnitude of pulsed seaweed inputs drives temporal variation in the top-down effects of lizard predators. Short-term weakening of lizard effects on spiders and plants (the latter via a trophic cascade) were associated with lizard diet shifts, and were more pronounced with larger seaweed inputs. Long-term strengthening of lizard effects was associated with lizard numerical responses and plant fertilisation. Increased pulse frequency reinforced the strengthening of lizard effects on spiders and plants. These results underscore the temporally variable nature of top-down effects and highlight the role of resource pulses in driving this variation.

Although global change can reshape ecosystems by triggering cascading effects on food webs, indirect interactions remain largely overlooked. Climate‐ and land‐use‐induced changes in landscape cause shifts in vegetation composition, which affect entire food webs. We used simulations of forest dynamics and movements of interacting species, parameterized by empirical observations, to predict the outcomes of global change on a large‐mammal food web in the boreal forest. We demonstrate that climate‐ and land‐use‐induced changes in forest landscapes exacerbate asymmetrical apparent competition between moose and threatened caribou populations through wolf predation. Although increased prey mortalities came from both behavioral and numerical responses, indirect effects from numerical responses had an overwhelming effect. The increase in caribou mortalities was exacerbated by the cumulating effects of land use over the short term and climate change impacts over the long term, with higher impact of land use. Indirect trophic interactions will be key to understanding community dynamics under global change. [ABSTRACT FROM AUTHOR]

Species traits and environmental conditions determine the occurrence and strength of trophic interactions. If we understand the relationship between these factors and trophic interactions, we can make more accurate predictions and build better trophic‐interaction models.We can compare traits and conditions by considering their effect on different parts (steps) of a trophic interaction, such as the steps search and pursuit. By linking traits to relevant steps, we can use these relationships to build trophic‐interaction models. Currently, this is done ad hoc, defining steps based on the species and traits of interest. This makes it difficult to compare across traits and species and gain an overarching understanding of how traits and the environment drive trophic interactions.We present a comprehensive approach for the explicit choice of interaction steps and species traits or environmental conditions, which is readily integrated into existing models. The core of this framework is that it is modular; we present eight steps that occur in all trophic interactions and use them to build a modular, general dynamic model. When applying the framework, one explicitly selects only the most relevant steps and uses those to build a specific model.To build our modular framework, we revisit and expand the functional and numerical response functions, dividing the trophic interaction into eight steps: (1) search, (2) prey detection, (3) attack decision, (4) pursuit, (5) subjugation, (6) ingestion, (7) digestion and (8) nutrient allocation. Together these steps form a general dynamical model where trophic interactions can be explicitly parameterized for multiple traits and environmental factors. We then concretize this approach by outlining how a specific community can be modelled by selecting key modules (steps) and parameterizing them for relevant factors. This we exemplify for a community of terrestrial arthropods using empirical data on body size and temperature responses.With species interactions at the core of community dynamics, our modular approach allows for quantification and comparisons of the importance of different steps, traits, and abiotic factors across ecosystems and trophic‐interaction types, and provides a powerful tool for trait‐based prediction of food‐web structure and dynamics. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

The use of alternative food for arthropod predators in augmentative and conservation biological pest control has increased considerably during the last two decades. Dozens of studies on this topic have been published, showing mixed effects. There are theoretical arguments to expect positive as well as negative effects of alternative food on pest control. In this review, we first discuss these arguments, resulting in a list of factors that potentially affect augmentative and conservation biocontrol with alternative food. We subsequently perform a meta-analysis of selected literature, which is mainly on control of various species of spider mites, thrips, whiteflies and chrysomelids, but also includes some studies on aphids, psyllids and mealybugs. The analysis reveals three factors that have significant effects on the way alternative food affects pest control. First, supplying alternative food should result in increases in the predator densities. Hence, there should be sufficient time for the predators to produce future generations during the cropping season. In the absence of such a numerical response, supplying alternative food can result in lower predation due to satiation of the predators, resulting in decreased pest control. Second, biocontrol is better when predators are released and provided with alternative food before pest invasion, allowing them to build up a population of predators that protects the crop. Third, when the alternative food consists of prey, it should not be of higher quality than the pest, otherwise predators may preferentially feed on the alternative prey, releasing the pest from predation. We furthermore analysed data on biocontrol of thrips, spider mite pests, whiteflies and chrysomelids for which enough data were available to disentangle effects of the various factors mentioned above. These analyses confirmed general results, from which guidelines for improvement of biocontrol of these specific pest groups can be derived. We also argue that the effects of alternative food on biocontrol should be studied by repeatedly assessing densities of pests and predators through time, preferably throughout a growing season. [ABSTRACT FROM AUTHOR]

Abstract Background Alloeocranum biannulipes Montr. and Sign.(Hemiptera: Reduviidae) is a predator present in stored yam chips and a promising biological control agent against Dinoderus porcellus Lesne (Coleoptera: Bostrichidae). Numerical responses of A. biannulipes to different densities (1, 2, 4, 6, and 8) of D. porcellus larvae were evaluated under ambient laboratory conditions (T°: 25 ± 2 °C; RH: 75–80%; photoperiod 12:12 h (L/D)). The number of consumed prey, duration of pre-oviposition and oviposition, number of eggs laid, pre-imaginal development times and mortality rate of the predator were recorded. Results The results revealed that A. biannulipes females preying on the highest larval density of D. porcellus (8) presented the highest predation rate (4.34 ± 0.18 larvae/predator/day), shortest pre-oviposition period (11.01 ± 0.57 days) and the highest oviposition period (15.83 ± 1.02 days). The daily number of eggs laid by A. biannulipes female (y) as a function of the number of D. porcellus larvae consumed (x) was modelled by the equation y = 0.158x 2 – 0.4073x + 3.8151 (R 2 = 0.571). The efficiency of prey conversion into eggs of A. biannulipes females decreased with increased prey density. The prey density did not affect the hatching rate of A. biannulipes eggs and the pre-imaginal development times. However, A. biannulipes nymphs fed with more (2 to 8) D. porcellus showed a significantly higher survival rate than those fed with a single larva. Conclusions The positive numerical response of A. biannulipes suggests that this predator could play a key role in biological control program against D. porcellus.

Abstract Although global change can reshape ecosystems by triggering cascading effects on food webs, indirect interactions remain largely overlooked. Climate‐ and land‐use‐induced changes in landscape cause shifts in vegetation composition, which affect entire food webs. We used simulations of forest dynamics and movements of interacting species, parameterized by empirical observations, to predict the outcomes of global change on a large‐mammal food web in the boreal forest. We demonstrate that climate‐ and land‐use‐induced changes in forest landscapes exacerbate asymmetrical apparent competition between moose and threatened caribou populations through wolf predation. Although increased prey mortalities came from both behavioral and numerical responses, indirect effects from numerical responses had an overwhelming effect. The increase in caribou mortalities was exacerbated by the cumulating effects of land use over the short term and climate change impacts over the long term, with higher impact of land use. Indirect trophic interactions will be key to understanding community dynamics under global change.

The Comparative Functional Response Approach (CFRA) was developed to provide a practical methodology by which short-term experiments can be used to forecast the longer-term impacts of a potential invading consumer. The CFRA makes inferences about potential invader impact based on comparisons of the functional responses of invader and native consumers on native resources in a common experimental venue. Application of the CFRA and derivative approaches have proliferated since it was introduced in 2014. Here we examine the conceptual foundations of the CFRA within the context of basic Lotka–Volterra consumer-resource theory. Our goals are to assess whether core predictions of the CFRA hold within this framework, to consider the relative importance of background mortality and consumer assimilation efficiency in determining predator impact, and to leverage this conceptual framework to expand the discussion regarding stability and long term consumer and resource dynamics. The CFRA assertion that consumers with a higher functional response will have larger impacts on resources only holds as long as all other parameters are equal, but basic theory indicates that predator impacts on prey abundance and stability will depend more on variation in conversion efficiency and background mortality. While examination of the CFRA within this framework highlights limitations about its current application, it also points to potential strengths that are only revealed when a theoretical context is identified, in this case the implications for stability and conceptual links to competition theory. [ABSTRACT FROM AUTHOR]

We assessed the functional and numerical responses of Trichogramma brassicae Bezdenko under long-term rearing (45 generations, G5-G45) on eggs of a common factitious host, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). Under such long-term mass rearing, the function response of this parasitoid shifted from Type III (from G5 to G20) toType II (from G25 to G45).The maximum attack rate (T/Th) (33.62 hosts/day) and the shortest handling time (0.7138 ± 0.0272 h) were recorded in G5. Also, G45 had the lowest attack rate (21.67 hosts/day) and longest handling time (1.1076 ± 0.0689 h). The handling time increased gradually over the generations (P reg <0.01, R2 = 0.903). The number of eggs laid by the parasitoid increased significantly with increased host density, but reached a plateau at very high densities. While no significant differences in daily parasitism were observed over 45 generations at densities of 2, 4, 8, and 16 available host eggs per wasp, there were significant differences in parasitism at host densities of 32, 64, and 128 eggs per wasp. T. brassicae females were more active and foraged more frequently in earlier generations (G5 to G20), which allowed wasps to parasitize more E. kuehniella eggs compared to later generations. Also, continuous mass rearing of T. brassicae negatively affected foraging behavior and the quality of wasps after G20. However, rejuvenation of the colony by adding field-collected parasitoids or rearing wasps on more suitable factitious hosts is strongly recommended to lower the negative effects of long-term mass rearing on quality of this parasitoid. [ABSTRACT FROM AUTHOR]

Aggregation of conspecific predators sharing a common prey, influences their bodyweights. We investigated the influence of intraspecific competition of adult ladybirds of Coccinella transversalis Fabricius on their bodyweight feeding on rusty plum aphid, Hysteroneura setariae (Thomas). Adult males and females consumed a significantly greater number of aphids with increase in predator-density, however, the aphid-consumption per predator declined with this increase. The weight gain per predator also decreased linearly with increase in the density of both male and female predators. This indicates that the weight-gain of the predator is a function of the prey consumed. The searching efficiency decreased with increase in predator density due to mutual inference. The mutual interference constants for adult male and female ladybirds were −0.419 and −0.546, respectively. The females consumed a greater number of aphids than males. The killing power of the ladybird denoted by the k-value increased curvilinearly with increase in predator density. We conclude that prey consumption is a function of body size and that the offspring of those that aggregate at low densities in prey-rich habitats develop into large adults.

Predatory coccinellid, Cryptolaemus montrouzieri Mulsant is an important biological agent in citrus orchards. The effect of six treatments included: two types of mineral oils, EC and mayonnaise at the concentration of 15 ml/L, buprofezin 0.75 ml/L, buprofezin+EC oil 0.5+5 ml/L, insecticidal soap palizin 2.5 ml/L, and water as the control were investigated on the functional and numerical responses of C. montrouzieri Mulsant under laboratory conditions. The experiment investigated predation rate of female adult coccinellids to varying densities (2, 4, 8, 16, 32 and 64) of mealybug pray, Pseudococcus citri Risso. The relationship between the rate of consumption and pray density was explored with a logistic regression. The results of logistic regressions revealed that the rate of prey consumption by the predator had risen as prey density increased, but eventually leveled off in both the control and all insecticide treatments (following Holling's type II functional response). Comparison of attack rates showed that the parameter significantly decreased when the predator was exposed to all insecticides but palizin. Predator handling times for oil mayonnaise, buprofezin and buprofezin+ EC oil treatments were significantly longer than that of the control. The longest handling time (1.6065 h) and the lowest attack rate (0.0351 h-1) were estimated for buprofezin+oil and oil EC treatments, respectively. As prey density increased, increase in oviposition and decrease in the food exploitation efficiency were observed. The results confirmed that the functional response of C. montrouzieri was affected by tested compounds reducing the predatory potential. The exception was palizin that had a low effect on functional response events of treated C. montrouzieri. [ABSTRACT FROM AUTHOR]

Background: Alloeocranum biannulipes Montr. and Sign.(Hemiptera: Reduviidae) is a predator present in stored yam chips and a promising biological control agent against Dinoderus porcellus Lesne (Coleoptera: Bostrichidae). Numerical responses of A. biannulipes to different densities (1, 2, 4, 6, and 8) of D. porcellus larvae were evaluated under ambient laboratory conditions (T°: 25 ± 2 °C; RH: 75–80%; photoperiod 12:12 h (L/D)). The number of consumed prey, duration of pre-oviposition and oviposition, number of eggs laid, pre-imaginal development times and mortality rate of the predator were recorded. Results: The results revealed that A. biannulipes females preying on the highest larval density of D. porcellus (8) presented the highest predation rate (4.34 ± 0.18 larvae/predator/day), shortest pre-oviposition period (11.01 ± 0.57 days) and the highest oviposition period (15.83 ± 1.02 days). The daily number of eggs laid by A. biannulipes female (y) as a function of the number of D. porcellus larvae consumed (x) was modelled by the equation y = 0.158x2 – 0.4073x + 3.8151 (R2 = 0.571). The efficiency of prey conversion into eggs of A. biannulipes females decreased with increased prey density. The prey density did not affect the hatching rate of A. biannulipes eggs and the pre-imaginal development times. However, A. biannulipes nymphs fed with more (2 to 8) D. porcellus showed a significantly higher survival rate than those fed with a single larva. Conclusions: The positive numerical response of A. biannulipes suggests that this predator could play a key role in biological control program against D. porcellus. [ABSTRACT FROM AUTHOR]

Abstract Density‐dependent regulation is an important process in spatio‐temporal population dynamics because it can alter the effects of synchronizing processes operating over large spatial scales. Most frequently, populations are regulated by density dependence when higher density leads to reduced individual fitness and population growth, but inverse density dependence can also occur when small populations are subject to higher extinction risks. We investigate whether density‐dependent regulation influences population growth for the Antarctic breeding Adélie penguin Pygoscelis adeliae. Understanding the prevalence and nature of density dependence for this species is important because it is considered a sentinel species reflecting the impacts of fisheries and environmental change over large spatial scales in the Southern Ocean, but the presence of density dependence could introduce uncertainty in this role. Using data on population growth and indices of resource availability for seven regional Adélie penguin populations located along the East Antarctic coastline, we find compelling evidence that population growth is constrained at some locations by the amount of breeding habitat available to individuals. Locations with low breeding habitat availability had reduced population growth rates, higher overall occupancy rates, and higher occupancy of steeper slopes that are sparsely occupied or avoided at other locations. Our results are consistent with evolutionary models of avian breeding habitat selection where individuals search for high‐quality nest sites to maximize fitness returns and subsequently occupy poorer habitat as population density increases. Alternate explanations invoking competition for food were not supported by the available evidence, but strong conclusions on food‐related density dependence were constrained by the paucity of food availability data over the large spatial scales of this region. Our study highlights the importance of incorporating nonconstant conditions of species–environment relationships into predictive models of species distributions and population dynamics, and provides guidance for improved monitoring of fisheries and climate change impacts in the Southern Ocean.

Feeding potential and foraging behaviour are two important factors which determine the predator's efficiency of managing prey. Predator-prey system of Cheilomenes sexmaculata (Fabricius) and Aphis gossypii Glover was evaluated to find out the predation efficiency. Feeding potential was observed for different stages of C. sexmaculatus on A. gossypii whereas, functional and numerical responses were ascertained as a function of prey/host density. For the grub stage, highest feeding potential (101.43 ± 3.04 aphids) was observed for the fourth instar which was higher than the gross feeding potential of all other instars. Among the adults, female recorded high feeding potential with a mean daily consumption of 43.13 ± 0.54 aphids. Life table studies showed intrinsic rate of increase (r) of 0.22 with the mean generation time of 27.29 days. The foraging behaviour studies revealed that all the grub stages and adults displayed a type-II functional response. The IV instar grub has shown the lowest handling time with highest maximum predation (96.1aphids/day), followed by female (94.6), male (82.6) and other stages. However, female depicted a rapid extinction of aphid by keeping it below 25, as against fourth instar grub and male which affected extinction by keeping it below 30. So, the releases of fourth instar grub and female of C. sexmaculatus could be advocated for the augmentative biological control of A. gossypii. [ABSTRACT FROM AUTHOR]

We considered how environmental variation and adaption together constrain energy acquisition of a keystone predator and how the constraints might influence its ecological function. We tested the proposition that changing energy availability, occurring as shifts in shore level and size composition of the lower vertical boundary of intertidal mussel beds (Mytilus spp.), affects energy storage and growth of predatory sea stars, Pisaster ochraceus. Energy storage of Pisaster (mass of the pyloric caeca, PC) increased when highly variable inter‐annual mussel recruitment temporarily shifted the lower boundary of the mussel bed down‐shore; energy storage decreased when the lower boundary receded up‐shore. Greatest storage occurred during massive recruitment of juvenile mussels, which caused the largest downward extensions of the boundary. To test the causal basis of the storage–boundary correlation, sea stars collected from sites with natural episodes of massive mussel recruitment were tagged and translocated to sites with experimentally shifted boundaries. On mussel beds with lower boundaries artificially expanded downward, the sea stars sustained high energy storage over most of the range of initial sizes. On mussel beds left unaltered or experimentally recessed, they lost PC mass. The amounts of loss were similar between unaltered and recessed treatments. We suggest an explanation for this unexpected similarity. Pisaster aggregate and disperse in response to the inter‐annual variation in mussel recruitment, and this numerical response is integral to mechanisms holding stationary the lower boundary, imposing stability on the local mussel population. Inter‐annual episodes of massive mussel recruitment, which have the potential to abruptly destabilize the lower boundaries, (1) elicit the strongest numerical response and (2) incur the greatest energy storage. The amount of energy storage in the season of active foraging is approximately proportional to the reproductive output in the subsequent reproductive season. Therefore, we propose that the system property of prey population stability originates in energy constraints underpinning Darwinian fitness of a keystone predator. Study limitations and further tests of the hypothesis are described. [ABSTRACT FROM AUTHOR]

BACKGROUND: This study evaluated the potential of Neoseiulus cucumeris Oudemans and Amblyseius swirskii Athias‐Henriot (Acari: Phytoseiidae) for controlling western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), by determining the functional response, numerical response, prey switching and mutual interference behaviors of the predators. RESULTS: A type II functional response was detected for two predator species fed on WFT first instars. The attack rate was higher for A. swirskii than N. cucumeris, but the handling time of N. cucumeris was shorter. For two predator species, numerical response was affected by both prey density and oviposition time. The per capita searching efficiencies of the two predators decreased significantly with increasing predator densities. The interference coefficient for A. swirskii was less than that of N. cucumeris. Although N. cucumeris switched from feeding on WFT first instars to feeding on second instars, this behavior was not observed in A. swirskii. CONCLUSIONS: Comparison of the two predator species foraging behaviors indicated optimal performance by A. swirskii at lower F. occidentalis densities. N. cucumeris was found to perform optimally at relatively higher prey densities. Moreover, N. cucumeris could be more effective in stabilizing the predator–prey system by switching behavior compared with A. swirskii. At higher predator densities, A. swirskii seemed to be an effective agent owing to its reduced intraspecific competition compared with N. cucumeris. Findings from this study will be useful in selecting appropriate agents and developing effective biocontrol programs to control WFT. © 2021 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Predicting the myriad effects of climate change on ecological communities is a major challenge for scientists, and to date relatively few studies have focused on the effects of sea freshening on species interactions. In particular, changes in keystone species predatory effects could be pervasive. Here, we assess the consequences of decreasing salinity on the ecological impact exerted by a keystone predatory sea star, Asterias rubens. We quantified sea star functional responses (FRs; per capita predation as a function of prey density) under decreasing salinity treatments aligned with climate change projections (18ppt, 15ppt, 12ppt). Furthermore, we combined FRs with larval recruitment estimates, i.e. ecological “Impact Potential”, to act as an ecological indicator of predator population-level responses under this environmental change. Attack and maximum feeding rates of sea stars were reduced by decreasing salinities, with no instances of predation found at 12ppt. Given that decreasing salinities also reduced larval sea star recruitment, the overall Impact Potential of this keystone predator species was lessened by decreased salinity. Sea freshening projections by the end of this century could thus drive significant decreases in the effects of this keystone predator, with serious implications for the structuring and functioning of ecological communities.

Abstract We considered how environmental variation and adaption together constrain energy acquisition of a keystone predator and how the constraints might influence its ecological function. We tested the proposition that changing energy availability, occurring as shifts in shore level and size composition of the lower vertical boundary of intertidal mussel beds (Mytilus spp.), affects energy storage and growth of predatory sea stars, Pisaster ochraceus. Energy storage of Pisaster (mass of the pyloric caeca, PC) increased when highly variable inter‐annual mussel recruitment temporarily shifted the lower boundary of the mussel bed down‐shore; energy storage decreased when the lower boundary receded up‐shore. Greatest storage occurred during massive recruitment of juvenile mussels, which caused the largest downward extensions of the boundary. To test the causal basis of the storage–boundary correlation, sea stars collected from sites with natural episodes of massive mussel recruitment were tagged and translocated to sites with experimentally shifted boundaries. On mussel beds with lower boundaries artificially expanded downward, the sea stars sustained high energy storage over most of the range of initial sizes. On mussel beds left unaltered or experimentally recessed, they lost PC mass. The amounts of loss were similar between unaltered and recessed treatments. We suggest an explanation for this unexpected similarity. Pisaster aggregate and disperse in response to the inter‐annual variation in mussel recruitment, and this numerical response is integral to mechanisms holding stationary the lower boundary, imposing stability on the local mussel population. Inter‐annual episodes of massive mussel recruitment, which have the potential to abruptly destabilize the lower boundaries, (1) elicit the strongest numerical response and (2) incur the greatest energy storage. The amount of energy storage in the season of active foraging is approximately proportional to the reproductive output in the subsequent reproductive season. Therefore, we propose that the system property of prey population stability originates in energy constraints underpinning Darwinian fitness of a keystone predator. Study limitations and further tests of the hypothesis are described.

Predation is one of the significant biotic mortality factors reducing the insect pest population as functional response and the numerical response of the predator are the key factor regulating the population dynamics of predator prey species. This study is aimed to evaluate the functional response of all the developmental stages of Scymnus coccivora Ayyar (Coleoptera: Coccinellidae) against the different densities of cotton mealybug, Phenacoccus solenopsis (Tinsley) (Hemiptera: Pseudococcidae) and the numerical response of female predator. Experiments were carried out in controlled environment laboratory conditions at 25 ± 1 °C temperature, 60 ± 5% relative humidity and photoperiod of 16 h. Number of eggs consumed, number of eggs laid and the Efficiency of Conversion of Ingested food (ECI) were recorded daily. Results from the study revealed that all the developmental stages of S. coccivora exhibited a Type II response. Different parameters such as attack rate (a'), handling time (T h) and the maximum rate of predation were estimated using Roger's random attack equation and Holling Disc equation in which Rogers random attack equation was found best fit. Female has shown the highest attack rate (a') followed by IVth instar grub, male, IIIrd, IInd and Ist instar grub. With low handling time, IVth instar grub has shown maximum predation rate of 76.40 per day followed by female (75.86), male (58.79), IIIrd (22.84), IInd (19.65) and Ist instar grub (15.39). The numerical response increase was curvilinearly related to different prey densities with the highest number of eggs (11.8 ± 3.44) produced at highest prey density (160). The Efficiency of Conversion of Ingested food (ECI) was highest (64.49 ± 8.03) at prey density of 10. Understanding the factors that lead to variation in functional response of predator in natural population will advance our understanding of the effects of predation on individual and the effectiveness of coccinellid predators as biocontrol agent against cotton mealybug. [ABSTRACT FROM AUTHOR]

Interactions between herbivores and their predators are shaped, in part, by plant phenotype. Consequently, ubiquitous symbionts of plants below‐ground, such as arbuscular mycorrhizal fungi (AMF), may influence interactions above‐ground between predators and their prey by altering plant phenotype. However, the ecological relevance of below‐ground organisms on predator–prey interactions under field conditions remains unclear.We assessed how AMF influence herbivore–predator interactions through a field experiment.We planted two milkweed species (Asclepias curassavica and Asclepiasincarnata) provided with different amounts of AMF inoculum (zero, medium, and high) in a randomized block design. We added aphids to plants and reduced predator pressure weekly for 5 weeks to evaluate effects of AMF on predator recruitment. We then allowed herbivore–predator interactions to re‐establish naturally for the remainder of the season to examine whether AMF‐mediated variation in predator recruitment influenced the suppression of aphid populations.Arbuscular mycorrhizal fungi availability in soils mediated interactions between predaceous aphid midge flies Aphidoletes aphidimyza and their aphid prey Aphis nerii, but the effects were plant species‐specific. On A. curassavica, by mid‐season, midges were recruited most strongly on plants under medium AMF availability and least on plants under high AMF availability. In contrast, each midge killed fewer aphids with increasing aphid density on medium AMF plants, but killed more aphids with increasing aphid density on high AMF plants. In combination, aphid mortality rates imposed by midges were greatest on medium AMF plants, followed by high and zero AMF plants. By comparison, on A. incarnata, the recruitment of midges was strongest on high AMF plants and weakest on medium AMF plants. AMF had no effect on the number of aphids killed per midge, relative to aphid density, so mortality rates of aphids imposed by midges mirrored recruitment. Rates of decline in aphid populations following predator recolonization were associated with midge densities, as well as lacewing and syrphid densities, which were unaffected by AMF availability. Therefore, the effects of AMF on aphid population decline were not a simple function of AMF–midge interactions.Our findings demonstrate that the availability of AMF in soils has pervasive, but complex, effects on predator–herbivore dynamics in the field. [ABSTRACT FROM AUTHOR]

Parameters that describe foraging behavior play a key role in selection of natural enemies used in biological control programs. These parameters are greatly affected by patch condition and food source type. This study was carried out to evaluate foraging behavior in Neoseiulus barkeri (Hughes) (Acari: Phytoseiidae), a predatory mite of Tetranychus urticae Koch under different patch and diet conditions. The predation rate of N. barkeri at different egg and nymph densities of T. urticae (2, 4, 8, 16, 32, 64, 128) was investigated in both limited and unlimited patches either in the presence or absence of pollen as an additional food source under laboratory conditions. A Type II functional response was determined for N. barkeri on eggs or nymphs of T. urticae in both unlimited and limited patches. The type of functional response was not affected by presence or absence of pollen. The numerical response, in terms of eggs laid, increased curvilinear with increasing prey density. The numerical response was similar in shape to a Type II functional response. The efficiency of conversion of ingested food (ECI) of female N. barkeri decreased in all treatments when prey density increased. The type of patch (limited or unlimited) and prey stage (egg or nymph in the presence or absence of pollen) can affect searching efficiency (a) and handling time (Th) (functional response) as well as daily fecundity and ECI (numerical response) of the phytoseiid predator mite, N. barkeri with implications for its use in biological control. [ABSTRACT FROM AUTHOR]

The red palm mite, Raoiella indica Hirst (Acari: Tenuipalpidae), is a severe pest of coconut (Cocos nucifera L.), banana (Musa sp.), and some ornamental palms. The predatory mite Amblyseius largoensis Muma (Acari: Phytoseiidae) has been reported in association with R. indica in several countries. Here, we assessed the interaction effect between prey density and population structure on predation and fecundity of this phytoseiid species. Specifically, we estimated the predation capacity of nymphs and females of A. largoensis based on their functional and numerical responses when fed on eggs, immature stages (deutonymphs or protonymphs), and females of R. indica. Nymphs and females of A. largoensis presented type II functional responses to R. indica, except for nymphs of the predator when consuming immature stages of the pest that exhibited a type III functional response. Nymphs and females of the predator showed a higher attack rate and shorter handling time when feeding on eggs of R. indica than on immatures and females. The highest oviposition rates of A. largoensis were observed when eggs and immatures of the pest were offered as prey. The results indicate that nymphs and females of A. largoensis may be effective in suppressing R. indica populations, mainly at lower prey densities. [ABSTRACT FROM AUTHOR]

We conducted microcosm experiments with two contrasting freshwater ciliates on functional traits (FTs) related to their growth rate (numerical response, NR) and ingestion rate (functional response, FR) over a range of ecologically relevant temperatures. Histiobalantium bodamicum and Vorticella natans are common planktonic ciliates but their abundance, swimming behavior, and temperature tolerance are different. In contrast to most sessile peritrich species, the motile V. natans is not strictly bacterivorous but also voraciously feeds upon small algae. We observed three main alterations in the shape of NR of both species with temperature, that is, change in the maximum growth rate, in the initial slope and in the threshold food level needed to sustain the population. Similarly, maximum ingestion rate, gross growth efficiency (GGE), and cell size varied with temperature and species. These findings caution against generalizing ciliate performance in relation to the ongoing global warming. Our results suggest that V. natans is the superior competitor to H. bodamicum in terms of temperature tolerance and bottom‐up control. However, the abundance of V. natans is usually low compared to H. bodamicum and other common freshwater ciliates, suggesting that V. natans is more strongly top‐down controlled via predation than H. bodamicum. The taxonomic position of V. natans has been debated. Therefore, to confirm species and genus affiliation of our study objects, we sequenced their small subunit ribosomal RNA (SSU rDNA) gene. [ABSTRACT FROM AUTHOR]

Aggregation of conspecific predators sharing a common prey, influences their bodyweights. We investigated the influence of intraspecific competition of adult ladybirds of Coccinella transversalis Fabricius on their bodyweight feeding on rusty plum aphid, Hysteroneura setariae (Thomas). Adult males and females consumed a significantly greater number of aphids with increase in predator-density, however, the aphid-consumption per predator declined with this increase. The weight gain per predator also decreased linearly with increase in the density of both male and female predators. This indicates that the weight-gain of the predator is a function of the prey consumed. The searching efficiency decreased with increase in predator density due to mutual inference. The mutual interference constants for adult male and female ladybirds were -0.419 and -0.546, respectively. The females consumed a greater number of aphids than males. The killing power of the ladybird denoted by the k-value increased curvilinearly with increase in predator density. We conclude that prey consumption is a function of body size and that the offspring of those that aggregate at low densities in prey-rich habitats develop into large adults. [ABSTRACT FROM AUTHOR]

Oligotrich ciliates play a key role in linking microbial food webs to the traditional grazing food chain. Hence, the numerical (growth) and functional (grazing) responses of oligotrich ciliates are very important issues in studies of marine ecosystems. Most oligotrich ciliates feed mainly on nanoflagellates, while some of them also have the ability to consume bacteria. Up until now, studies of ciliates grazing on algae have not specifically excluded the effects of bacteria. In the present study, we found that the presence of bacteria in the algal culture medium affected the growth and grazing rates of ciliates grazing on nanoflagellates, resulting in an overestimate of gross growth efficiency at low relative algal concentrations. Strombidium sp. is prey selective mainly grazing on bacteria at low relative algal concentrations, but on algae at high relative algal concentrations. Carbon obtained from ciliate grazing on bacteria should be taken into account in the coastal zone surveys and especially in culture experiments to avoid unreasonable results of carbon flow.

In this paper we introduce a formal method for the derivation of a predator's functional response from a system of fast state transitions of the prey or predator on a time scale during which the total prey and predator densities remain constant. Such derivation permits an explicit interpretation of the structure and parameters of the functional response in terms of individual behaviour. The same method is also used here to derive the corresponding numerical response of the predator as well as of the prey. [ABSTRACT FROM AUTHOR]

Predators relying on a particular prey as their main food resource are especially susceptible to fluctuation in prey availability. When prey abundance decreases they show a functional response by adjusting their diet. After this, predators may suffer a numerical response. These responses have been poorly studied in presence of alien invasive preys. The black-chested buzzard-eagle (Geranoaetus melanoleucus) is a large raptor inhabiting open areas of South America. Here we present the first long-term study on this eagle population tendency, analyzing functional and numerical responses associated with changes in the abundance of the exotic European hare (Lepus europaeus). We measured breeding performance and studied eagles' diet during the breeding seasons of 1991, 1992, 2006, 2011 and 2012. We also estimated the relative abundance of hares in those years. Eagles diets changed over the years with a decrease in hare consumption. The number of eagles decreased from 1992 to less than half in 2012. Forty one percent of the total eagles observed in 1991/92, and 27% in 2006 were immature, while in 2011 and 2012 no immature were observed. We found similar tendencies of decrease in the abundance of hares which suggest that the decrease in eagles population may be related with the decreasing tendency of hares. No other factor that may have affected immature eagles abundance was evident in the area during this period. Our data suggest that changes in the abundance of an exotic lagomorph may lead numerical and functional responses in a top predator by affecting its diet, age structure, and ultimately abundance. [ABSTRACT FROM AUTHOR]

Invasive alien species continue to arrive in new locations with no abatement in rate, and thus greater predictive powers surrounding their ecological impacts are required. In particular, we need improved means of quantifying the ecological impacts of new invasive species under different contexts. Here, we develop a suite of metrics based upon the novel Relative Impact Potential (RIP) metric, combining the functional response (consumer per capita effect), with proxies for the numerical response (consumer population response), providing quantification of invasive species ecological impact. These metrics are comparative in relation to the eco-evolutionary baseline of trophically analogous natives, as well as other invasive species and across multiple populations. Crucially, the metrics also reveal how impacts of invasive species change under abiotic and biotic contexts. While studies focused solely on functional responses have been successful in predictive invasion ecology, RIP retains these advantages while adding vital other predictive elements, principally consumer abundance. RIP can also be combined with propagule pressure to quantify overall invasion risk. By highlighting functional response and numerical response proxies, we outline a user-friendly method for assessing the impacts of invaders of all trophic levels and taxonomic groups. We apply the metric to impact assessment in the face of climate change by taking account of both changing predator consumption rates and prey reproduction rates. We proceed to outline the application of RIP to assess biotic resistance against incoming invasive species, the effect of evolution on invasive species impacts, application to interspecific competition, changing spatio-temporal patterns of invasion, and how RIP can inform biological control. We propose that RIP provides scientists and practitioners with a user-friendly, customisable and, crucially, powerful technique to inform invasive species policy and management. [ABSTRACT FROM AUTHOR]

Density‐dependent regulation is an important process in spatio‐temporal population dynamics because it can alter the effects of synchronizing processes operating over large spatial scales. Most frequently, populations are regulated by density dependence when higher density leads to reduced individual fitness and population growth, but inverse density dependence can also occur when small populations are subject to higher extinction risks. We investigate whether density‐dependent regulation influences population growth for the Antarctic breeding Adélie penguin Pygoscelis adeliae. Understanding the prevalence and nature of density dependence for this species is important because it is considered a sentinel species reflecting the impacts of fisheries and environmental change over large spatial scales in the Southern Ocean, but the presence of density dependence could introduce uncertainty in this role. Using data on population growth and indices of resource availability for seven regional Adélie penguin populations located along the East Antarctic coastline, we find compelling evidence that population growth is constrained at some locations by the amount of breeding habitat available to individuals. Locations with low breeding habitat availability had reduced population growth rates, higher overall occupancy rates, and higher occupancy of steeper slopes that are sparsely occupied or avoided at other locations. Our results are consistent with evolutionary models of avian breeding habitat selection where individuals search for high‐quality nest sites to maximize fitness returns and subsequently occupy poorer habitat as population density increases. Alternate explanations invoking competition for food were not supported by the available evidence, but strong conclusions on food‐related density dependence were constrained by the paucity of food availability data over the large spatial scales of this region. Our study highlights the importance of incorporating nonconstant conditions of species–environment relationships into predictive models of species distributions and population dynamics, and provides guidance for improved monitoring of fisheries and climate change impacts in the Southern Ocean. [ABSTRACT FROM AUTHOR]

Abstract Background High latitude ecosystems are at present changing rapidly under the influence of climate warming, and specialized Arctic species at the southern margin of the Arctic may be particularly affected. The Arctic fox (Vulpes lagopus), a small mammalian predator endemic to northern tundra areas, is able to exploit different resources in the context of varying tundra ecosystems. Although generally widespread, it is critically endangered in subarctic Fennoscandia, where a fading out of the characteristic lemming cycles and competition with abundant red foxes have been identified as main threats. We studied an Arctic fox population at the Erkuta Tundra Monitoring site in low Arctic Yamal (Russia) during 10 years in order to determine which resources support the breeding activity in this population. In the study area, lemmings have been rare during the last 15 years and red foxes are nearly absent, creating an interesting contrast to the situation in Fennoscandia. Results Arctic fox was breeding in nine of the 10 years of the study. The number of active dens was on average 2.6 (range 0–6) per 100 km2 and increased with small rodent abundance. It was also higher after winters with many reindeer carcasses, which occurred when mortality was unusually high due to icy pastures following rain-on-snow events. Average litter size was 5.2 (SD = 2.1). Scat dissection suggested that small rodents (mostly Microtus spp.) were the most important prey category. Prey remains observed at dens show that birds, notably waterfowl, were also an important resource in summer. Conclusions The Arctic fox in southern Yamal, which is part of a species-rich low Arctic food web, seems at present able to cope with a state shift of the small rodent community from high amplitude cyclicity with lemming dominated peaks, to a vole community with low amplitude fluctuations. The estimated breeding parameters characterized the population as intermediate between the lemming fox and the coastal fox ecotype. Only continued ecosystem-based monitoring will reveal their fate in a changing tundra ecosystem.

• Companion planting resulted in reduced initial aphid densities. • Companion plants mediated reduced parasitoid emergence. • Companion plants affected natural enemy numerical response. • Companion plants interacted with aphid density to affect natural enemy. Engineering agricultural habitats to increase resources for natural enemies has been widely adopted for promoting conservation biological control of arthropod pests. In this context, companion planting (i.e., intercropping) has been a common habitat manipulation used for bolstering the abundance of natural enemies by means of providing them with alternative food and shelter. However, the mechanistic understanding of how companion plants interact with the target crop, as well as with the pest and natural enemy community to influence biological control, remains poorly understood. In this field study, we assessed how companion plants (i.e., non-flowering parsley) intercropped with collard greens could affect the natural infestation by aphids, natural enemy activity and parasitoid emergence. Aphid densities were significantly lower in companion plant treatments over the first four weeks of the experiment, which likely reflected increased predation by sheltered generalist predators. The results also suggest that companion planting can indirectly influence the time and strength of specialist natural enemies' numerical response. Moreover, companion planting was associated with lower parasitoid emergence, which was likely a response to increased intraguild predation. It appears that by mediating a lower aphid density, companion plants may breakdown the dilution effect and consequently promote higher predation of mummies by generalist predators. Lastly, reducing aphid density through companion planting in the brassica system is appealing since Brazilian growers have a limited number of insecticides registered for aphids, which have been a detrimental pest that often turns the collard leaves unmarketable due to stunted growth. [ABSTRACT FROM AUTHOR]