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Most terrestrial large mammals went extinct on different continents at the end of the Pleistocene, between 50,000 and 10,000 years ago. Besides the loss in species diversity and the truncation of body mass distributions, those extinctions were even more impactful to interaction diversity. Along with each extinction, dozens of ecological interactions were lost, reorganizing species interaction networks, which attained species-poor configurations with low functional redundancy. Extinctions of most large herbivores impacted energy flow and the rates of nutrient cycling, reconfiguring ecosystem-level networks. Because large mammals have high mobility, their loss also shortened seed-dispersal distance and reduced nutrient diffusivity, disrupting spatial networks. This review examines the recent advances in understanding how different types of ecological networks have been restructured by megafaunal extinctions and how this reorganization affected ecosystem functions. Megafaunal extinctions resulted in the loss of multiple ecological interactions in terrestrial systems. Interaction loss reshaped different types of ecological networks including food webs and spatial networks. The reorganization of ecological networks changed how terrestrial ecosystems are structured and function. [ABSTRACT FROM AUTHOR]

Most demonstrated trophic cascades originate with predators, but infectious agents can also cause top-down indirect effects in ecosystems. Here we synthesize the literature on trophic cascades initiated by infectious agents including parasitoids, pathogens, parasitic castrators, macroparasites, and trophically transmitted parasites. Like predators, infectious agents can cause density-mediated and trait-mediated indirect effects through their direct consumptive and nonconsumptive effects respectively. Unlike most predators, however, infectious agents are not fully and immediately lethal to their victims, so their consumptive effects can also trigger trait-mediated indirect effects. We find that the frequency of trophic cascades reported for different consumer types scales with consumer lethality. Furthermore, we emphasize the value of uniting predator–prey and parasite–host theory under a general consumer–resource framework. [ABSTRACT FROM AUTHOR]

Trophic cascade theory predicts that apex predators structure ecosystems by regulating mesopredator and herbivore abundance and behaviour. Studies on trophic cascades have typically focused on short linear chains of species interactions. A framework that integrates more realistic and complex interactions is needed to make broader predictions on ecosystem structuring., Network analysis is used to study food webs and other types of species interaction networks. These often comprise large numbers of species but rarely account for multiple interaction types and strengths. Here, we develop an intermediate complexity theoretical framework that allows specification of multiple interaction types and strengths for the study of trophic cascades. This ecological network is designed to suit data typically derived from field-based studies. The trophic cascade network contains fewer nodes than food webs, but provides semi-weighted directional links that enable different types of interactions to be included in a single model., We use this trophic cascade network model to explore how an apex predator shapes ecosystem structure in an Australian arid ecosystem. We compared two networks that contrasted in the dominance of an apex predator, the dingo ( Canis dingo), using published results ranking the direction and strength of key interactions. Nodes and links interacted dynamically to shape these networks. We examined how changes to an apex predator population affect ecosystem structure through their direct and indirect influences on different components of this ecological community., Under strong apex predator influence, the network structure was denser and more complex, even and top-down driven; and dingo predation and soil commensalism formed denser interactive modules. Under weak apex predator influence (e.g. reflecting predator control), the resulting network structure was frayed, with mesopredator predation and grazing forming modules., Our study demonstrates that networks of intermediate complexity can provide a powerful tool for elucidating potential ecosystem-wide effects of apex predators and predicting the consequences of management interventions such as predator control. Integrating trophic cascades, with their array of complex interactions, with the three-dimensional structure of ecological networks, has the potential to reveal 'ecological architecture' that neither captures on its own. [ABSTRACT FROM AUTHOR]

Community structure and interspecific interactions are particularly vulnerable to rapidly changing climatic regimes. Recent changes in both climate and vertebrate community assemblages have created a unique opportunity to examine the impacts of two dynamic forces on population regulation. We examined the effects of warming winter conditions and the reestablishment of a previously extirpated predator, the fisher (Martes pennanti), on regulatory mechanisms in a northern-adapted mammal, the porcupine (Erethizon dorsatum), along their southern range boundary. Using a long-term (17-year) capture-recapture data set, we (1) quantified the impacts of climate change and increased fisher predation on the survival of adult porcupines at their regional southern terminus, (2) assessed recruitment (via both adult fecundity and juvenile survival) of porcupines, and (3) modeled the relative importance of predation and winter conditions on the demography and population growth rate (λ). Severe winters and abundant predators interacted synergistically to reduce adult survivorship by as much as 44%, while expanding predator populations led to near reproductive failure among porcupines. Increasing predatory pressure, disruptions in this community module, and more frequent extreme winter weather events led to predicted extirpation within 50 years, whereas in the absence of predators, the population was viable. Our results provide a mechanistic understanding behind distributional shifts resulting from climate change and may be broadly relevant for predicting future distributional shifts in other northern-adapted mammalian species. [ABSTRACT FROM AUTHOR]

Novel assemblages of native and introduced species characterize a growing proportion of ecosystems worldwide. Some introduced species have contributed to extinctions, even extinction waves, spurring widespread efforts to eradicate or control them. We propose that trophic cascade theory offers insights into why introduced species sometimes become harmful, but in other cases stably coexist with natives and offer net benefits. Large predators commonly limit populations of potentially irruptive prey and mesopredators, both native and introduced. This top-down force influences a wide range of ecosystem processes that often enhance biodiversity. We argue that many species, regardless of their origin or priors, are allies for the retention and restoration of biodiversity in top-down regulated ecosystems. [ABSTRACT FROM AUTHOR]

Ecosystem-level models that trace flows of mass and energy to quantify species interactions are important tools in whole ecosystem-based approaches to managing marine resources. A critical input parameter for such models is an estimate of the consumption rates and biomasses of prey consumed by fish populations. Here we estimate the annual prey consumption of an abundant coastal piscivore, Arripis trutta, which may exert substantial top-down control on its prey over its broad latitudinal range (28-43°S) in the coastal waters off south-eastern (SE) Australia. Three independent techniques were used to estimate annual prey consumption at two environmentally-relevant temperatures, 15 and 20°C: experimental gastric evacuation experiments (coupled with stomach content analyses); bioenergetics modelling, and; empirical regression modelling. Each technique yielded a similar range of estimates with annual food consumed/biomass (Q/B) ranging from 3.20 to 4.02 at 15°C and 4.23 to 5.25 at 20°C. Using an estimated A. trutta stock biomass in SE Australia of 10,000t, total mean annual prey consumption was estimated to be 42,200t, consisting primarily (93%) of small zooplanktivorous teleosts, particularly Australian sardines Sardinops sagax (35%) and scads Trachurus spp. (30%). These results indicate that A. trutta do possess a top-down influence on the pelagic ecosystem of coastal SE Australia via consumption of considerable biomasses of small pelagic fish. However, despite the use of a maximum regional estimate of A. trutta abundance and the presence of at least two other ecologically similar predatory fish species with higher annual prey consumption rates in SE Australian coastal waters, A. trutta may remove only a small proportion (~15%) of the estimated spawning biomasses of its major prey species in this region annually. The multiple-technique approach used in this study has for the first time quantified the diet of A. trutta in SE Australia and provided broad and repeatable estimates of its annual prey consumption for use in ecosystem models designed to manage coastal fisheries resources in this region. [ABSTRACT FROM AUTHOR]

Top-down population regulation can influence the success of biological control agents when they are released into the field. Entomopathogenic nematodes ( EPNs) are used commonly in biological control programmes, but their efficacy suffers from poor persistence. Although abiotic soil conditions have been shown to reduce EPN persistence, consumption of infected insects by scavengers and of infective juvenile ( IJ) nematodes by predators may also regulate these populations. In the present study, the effects of different soil arthropods on EPNs in laboratory conditions were measured. It was hypothesised that arthropods commonly found in soil communities where EPNs are applied would consume cadavers of insects parasitised by the nematodes and the IJs themselves., Some species of scavengers consume EPN-infected insects. Crickets ( Gryllus bimaculatus De Geer), American cockroaches [ Periplaneta Americana (Linnaeus)], ants [ Tetramorium chefketi Forel and Pheidole pallidula (Nylander)], earwigs ( Labidura riparia Pallas), mites ( Sancassania polyphyllae Zachvatkin), and springtails ( Sinella curviseta Brook and Folsomia candida Willem) have different responses to nematode-killed insects. Results suggested that ants ( T. chefketi), cockroaches, mites, and earwigs fed on Steinernema-killed insects whereas neither crickets nor springtails consumed them., In the second part of the study, experiments were conducted to determine whether mites and springtails consumed IJ EPNs. Results showed that S. polyphyllae mites do not consume infective juveniles in soil, whereas both springtail species consumed significant numbers of the IJs., Top-down regulatory processes can be a limiting factor for EPN populations under laboratory conditions. Both host cadavers and IJs are consumed (albeit by different arthropods), so these results may help explain the difficulties associated with the persistence of EPN application to soil. [ABSTRACT FROM AUTHOR]

Density-dependent prey depletion around breeding colonies has long been considered an important factor controlling the population dynamics of colonial animals. 1–4 Ashmole proposed that as seabird colony size increases, intraspecific competition leads to declines in reproductive success, as breeding adults must spend more time and energy to find prey farther from the colony. 1 Seabird colony size often varies over several orders of magnitude within the same species and can include millions of individuals per colony. 5,6 As such, colony size likely plays an important role in determining the individual behavior of its members and how the colony interacts with the surrounding environment. 6 Using tracking data from murres (Uria spp.), the world's most densely breeding seabirds, we show that the distribution of foraging-trip distances scales to colony size0.33 during the chick-rearing stage, consistent with Ashmole's halo theory. 1,2 This pattern occurred across colonies varying in size over three orders of magnitude and distributed throughout the North Atlantic region. The strong relationship between colony size and foraging range means that the foraging areas of some colonial species can be estimated from colony sizes, which is more practical to measure over a large geographic scale. Two-thirds of the North Atlantic murre population breed at the 16 largest colonies; by extrapolating the predicted foraging ranges to sites without tracking data, we show that only two of these large colonies have significant coverage as marine protected areas. Our results are an important example of how theoretical models, in this case, Ashmole's version of central-place-foraging theory, can be applied to inform conservation and management in colonial breeding species. [Display omitted] • The distribution of foraging trips around murre colonies scaled to colony size0.33 • Colony size can be used to predict foraging areass over a large geographic scale • Foraging areas of most North Atlantic murre breeding populations are not within protected areas Seabird colony size can vary over several orders of magnitude. Colony size likely plays an important role in determining individual behavior. Using tracking data from murres, the world's most densely breeding seabirds, Patterson et al. show how the distribution of foraging-trip distances scales to colony size, consistent with Ashmole's halo theory. [ABSTRACT FROM AUTHOR]

Three newly isolated strains of flavobacteria from coastal aquifer sediments have been found to be predatory, lysing a range of live and pasteurized microbial prey. The three strains have been classified on the basis of 16S rRNA gene phylogeny as belonging to the recently described Olleya (strains VCSA23 and VCSM12) and Tenacibaculum (strain VCSA14A) genera. Two of the closest cultured relatives to the strain VCSA14A, Tenacibaculum discolor and Tenacibaculum gallaicum, were also found to be bacteriolytic. These five predatory strains exhibit gliding motility and have been observed to lyse prey cells after surrounding them with social swarms, similar to known predatory bacteria such as myxobacteria and members of the genus Lysobacter. Flavobacteria are often numerically significant in a wide variety of freshwater and marine environments, particularly in association with particles, and are thought to be involved in the degradation of biopolymeric substances. If predatory capability is widespread among flavobacteria, they may be a previously unrecognized source of ‘top-down’ bacterial mortality with an influence on the composition and activity of surrounding microbial communities. [ABSTRACT FROM AUTHOR]

The article presents a study which investigates the effect of benthic and pelagic predators on intertidal mussel population in the marine protected area in South Africa. The study uses various treatments including caged treatment, roof treatment, and fence treatment as well as factorial analysis of variance (ANOVA) to determine the effects of different types of predators on the juvenile mussel samples which were collected from Plettenberg Bay in July 2009. The results show that mussels which were exposed to all predators have 50% survival rate, and benthic and pelagic predators were well balanced on juvenile mussels predation. Moreover, the result of ANOVA reveals that mortality was lower in the full cage treatment and equal in treatments with fences, roofs, or no protection.

Abstract: Predation of herbivorous Lepidoptera larvae by insectivorous avifauna was estimated on Lindera benzoin in edge and interior habitats at two sites in eastern Pennsylvania (USA). Clay baits modeled after Epimecis hortaria (Geometridae) larvae, the primary herbivore of L. benzoin at our study sites, were used to estimate predation by birds. In both habitat types, models were placed on uninjured L. benzoin leaves as well as on leaves that had prior insect herbivore damage. Rates of model attack were greater, and model longevity reduced, in forest edge plots compared to interiors. Naturally occurring herbivore damage on L. benzoin was greater in forest interiors. However, model attack was not significantly greater on leaves with prior herbivory damage, suggesting that birds do not effectively use this type of leaf damage as a cue in their foraging. Our findings are consistent with a contribution of bird predation towards top-down control of herbivory in this system. We further discuss these results in a broader context considering the possible effects of habitat type on leaf quality, leaf defense, and herbivore performance. [Copyright &y& Elsevier]