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Multiple factors determine diet selection of herbivores. However, in many diet studies selection of single nutrients is studied or optimization models are developed using only one currency. In this paper, we use linear programming to explain diet selection by African elephant based on plant availability and nutrient and deterrent content over time. Our results indicate that elephant at our study area maximized intake of phosphorus throughout the year, possibly in response to the deficiency of this nutrient in the region. After adjusting the model to incorporate the effects of this deficiency, elephant were found to maximize nitrogen intake during the wet season and energy during the dry season. We reason that the increased energy requirements during the dry season can be explained by seasonal changes in water availability and forage abundance. As forage abundance decrease into the dry season, elephant struggle to satisfy their large absolute food requirements. Adding to this restriction is the simultaneous decrease in plant and surface water availability, which force the elephant to seek out scarce surface water sources at high energy costs. During the wet season when food becomes more abundant and energy requirements are satisfied easier, elephant aim to maximize nitrogen intake for growth and reproduction. Our study contributes to the emerging theory on understanding foraging for multiple resources. [ABSTRACT FROM AUTHOR]

Spatial variation in vital rates can affect the dynamics and persistence of a population. We evaluated the prediction that age-specific probabilities of survival and first reproduction for Weddell seals would vary as a function of birth location in Erebus Bay, Antarctica. We used multi-state mark–resight models and 25 years of data to estimate demographic rates for female seals. We predicted that probabilities of survival and first reproduction would be higher for seals born at near-shore colonies or more southerly-located colonies with consistent ice conditions. Contrary to predictions, results revealed higher age-specific probabilities of first reproduction at offshore colonies relative to near-shore colonies and no spatial variation in survival rates. For 7-year old females (average age at 1st reproduction=7.6 years old) born at offshore colonies to mothers aged 10.8 years (average maternal age), probability of first reproduction was 0.43 (SE=0.07), whereas probability of first reproduction for females born at near-shore colonies was 0.30 (SE=0.05) based on estimates from our top-ranked model. Breeding probabilities following first reproduction were also higher at offshore colonies. Thus, our results (1) provide evidence of spatial variation in breeding probabilities, (2) reveal the importance of birth location on a female's vital rates, and (3) suggest that the effect persisted for many years. Birth-colony effects may be attributed to spatial variation in prey availability, or to heterogeneity in female quality in this population. If females who are superior competitors consistently chose offshore colonies for pupping, pups born at these locations may have inherited those superior qualities and displayed higher probabilities of first reproduction, relative to seals born at other colonies. Further research into physical or food-related differences among colonies may offer insight into spatial variation in breeding probabilities documented in this paper. [ABSTRACT FROM AUTHOR]

Ecologists have recognized for decades the importance of spatial scale in ecological processes and patterns, as well as the complications scale poses for understanding ecological mechanisms. Here we highlight the opportunity attention to scale offers experimental ecology. Despite many advantages to considering scale, a review of the literature indicates that multi-scale experimental studies are rare. Although much work has focused on scale as a primary factor (e.g. island size), we draw attention to scale as a ‘lurking’ variable: one which influences the relationship between two or more variables that are not usually understood to be scale-dependent. We highlight three basic observations from which scale-dependence arises: abundance increases with area, environmental conditions vary across space, and the effect of an organism on its environment is spatially limited. From these arise first-order scale-dependence, which relates an ecological variable of interest to a measure of scale. Combining first-order relationships together, we can produce second-order scale-dependencies, which occur when the relationship between two or more variables is mediated by scale. It is these relationships that are of particular interest, as they have the potential to confound experimental results. Most ecological experiments have incorporated scale either implicitly or not at all. We suggest that an explicit consideration of scale could help resolve some long-standing debates when scale is turned from a lurking variable into a working variable. Finally, we review and evaluate four different experimental sampling designs and corresponding statistical analyses that can be used to address the effects of scale in ecological experiments. [ABSTRACT FROM AUTHOR]

Recent advances in nutritional ecology, particularly arising from Ecological Stoichiometry and the Geometric Framework for nutrition, have resulted in greater theoretical coherence and increasingly incisive empirical methodologies that in combination allow for the consideration of nutrient-related processes at many levels of biological complexity. However, these advances have not been consistently integrated into the study of sexual differences in reproductive investment, despite contemporary emphasis on the material costs associated with sexually selected traits (e.g. condition-dependence of exaggerated ornaments). Nutritional ecology suggests that material costs related to sex-specific reproductive traits should be linked to quantifiable underlying differences in the relationship between individuals of each sex and their foods. Here, we argue that applying nutritionally-explicit thought to the study of sexual reproduction should both deepen current understanding of sex-specific phenomena and broaden the tractable frontiers of sexual selection research. In support of this general argument, we examine the causes and consequences of sex-specific nutritional differences, from food selection and nutrient processing to sex-specific reproductive traits. At each level of biological organization, we highlight how a nutritionally-explicit perspective may provide new insights and help to identify new directions. Based on predictions derived at the individual level, we then consider how sex-specific nutrient limitation might influence population growth, and thus potentially broader patterns of life history evolution, using a simple population dynamics model. We conclude by highlighting new avenues of research that may be more accessible from this integrative perspective. [ABSTRACT FROM AUTHOR]

Parasites constitute an ideal system with which to investigate patterns and mechanisms of community structure and dynamics. Nevertheless, despite their prevalence in natural systems, parasites have been examined less often than other organisms traditionally used for testing hypotheses of community assembly. In the present study, we investigate possible effects of competitive interactions on patterns of distribution (co-occurrence) and density among a group of streblid bat flies parasitic on short-tailed fruit bats, Carollia perspicillata. Using null model analyses of species co-occurrence, we did not find evidence that competition affects the distribution of bat fly species across hosts. Moreover, when non-infested hosts were included, analyses showed evidence for interspecific aggregation, rather than for the segregation predicted by competition theory. Partial Pearson correlations among bat fly species densities showed no evidence of negative covariation in two of three cases. In the species pair for which a significant negative correlation was found, a visual analysis of plotted covariation indicated a constraint line, suggesting that competition between these two species might become operational only in some infracommunities when abundances of bat flies approach a maximum set by one or more limiting resources. Moreover, when a community-wide estimation of the significance of density compensation was calculated, the result was not significant. Overall, we find no evidence that competition influences the distribution of bat flies on their hosts, and mixed support for effects of competition on the densities of species. These results are consistent with the idea that competition plays a role in structuring natural communities, but in many systems its effects are context-dependent and might not be important relative to other factors. Wider analyses across taxonomic and environmental gradients and a detailed consideration of the different hypothesized effects of competition are necessary to fully understand the importance of competition on natural communities. [ABSTRACT FROM AUTHOR]

The recently proposed metabolic theory of ecology (MTE) claims to provide a mechanistic explanation for long known allometric relationships between mass and metabolic rate. The MTE postulates that these patterns of allometry are driven by the primary selective constraint of transport of energy and materials. However, recent evidence along several different lines has called into question both the adequacy and the universality of this mechanism. We review the accumulating body of literature on this subject, adding our own concerns and criticisms. In addition to other difficulties, we argue that MTE fails as a mechanistic explanation of mass versus metabolic rate allometries because: 1) circulatory cost minimization is not a tenable criterion for evolutionary optimization, 2) the Boltzmann type relationships on which MTE depends are inadequate descriptors of complex metabolic pathways, and 3) most of the hypotheses advanced by the MTE do not, in fact, depend on the proposed mechanism and therefore cannot be used to test the theory. We conclude that the MTE should be abandoned as a monolithic explanation for allometric patterns, and that a more realistic path toward a better understanding of allometry would be to consider multiple explanatory mechanisms for physiological allometries. [ABSTRACT FROM AUTHOR]

Despite recent, strong interest in the modelling of monocarpic perennial flowering strategies, little is known about how variation in demographic rates affects selection on optimal timing of flowering. Temporal variation may yield fluctuating selective pressures, or, if individuals experience time trends, selection for phenotypic plasticity. Here we report the results of a 3-year study in a large field population of the facultative biennial herb Digitalis purpurea, where we use field data on size-dependent growth, survival and fecundity to parameterize an existing optimisation model. We compare results from models using either deterministic or individually varying demographic rates to address the degree of fluctuating selection on the flowering strategy. In addition, we explore whether recent growing conditions influence the size-specific liability to flower. Model results differed widely between years; immediate onset of reproduction was predicted in 1999, strongly delayed reproduction in 2000. This reflected large differences in both growth and survival rates between years. Observed flowering sizes also varied between years, but were larger in 1999 than in 2000, contrary to model predictions. Incorporating individual variation in growth increased predicted optimal flowering sizes compared to models using deterministic growth, whereas the inclusion of individual survival variation had little effect. There was no significant effect of recent growth rate on flowering probability. Taken together, these results indicate highly fluctuating selection on the flowering strategy in D. purpurea, but no evidence of adaptive plasticity in response to current growing conditions. Fluctuating selection may contribute to maintain genetic variation for threshold size for flowering, and may partly explain the large within-season size-variation in flowering individuals found in natural populations of D. purpurea. [ABSTRACT FROM AUTHOR]

The importance to food-webs of trophic cul-de-sacs, species that channel energy flow away from higher trophic levels, is seldom considered outside of the pelagic systems in which they were first identified. On intertidal mudflats, inputs of detritus from saltmarshes, macroalgae or microphytobenthos are generally regarded as a major structuring force underpinning food-webs and there has been no consideration of trophic cul-de-sacs to date. A fully orthogonal three-factor experiment manipulating the density of the abundant gastropod, Pyrazus ebeninus, detritus and macrobenthic predators on a Sydney mudflat revealed large deleterious effects of the gastropod, irrespective of detrital loading or the presence of predators. Two months after experimental manipulation, the standing-stock of microphytobenthos in plots with high (44 per m2) densities of P. ebeninus was 20% less than in plots with low (4 per m2) densities. Increasing densities of P. ebeninus from low to high halved the abundance of macroinvertebrates and the average number of species. In contrast, the addition of detritus had differing effects on microphytobenthos (positively affected) and macroinvertebrates (negatively affected). Over the two-months of our experiment, no predatory mortality of P. ebeninus was observed and high densities of P. ebeninus decreased impacts of predators on macroinvertebrate abundances. Given that the dynamics of southeast Australian mudflats are driven more by disturbance than seasonality in predators and their interactions with prey, it is likely that Pyrazus would be similarly resistant to predation and have negative effects on benthic assemblages at other times of the year, outside of our study period. Thus, in reducing microphytobenthos and the abundance and species richness of macrofauna, high abundances of the detritivore P. ebeninus may severely limit the flow of energy up the food chain to commercially-important species. This study therefore suggests that trophic cul-de-sacs are not limited to the eutrophied pelagic systems in which they were first identified, but may exist in other systems as well. [ABSTRACT FROM AUTHOR]

The evolution of eusociality, where some individuals altruistically forgo reproduction, poses a dilemma which can be solved by kin selection, i.e. by considering relatedness among cooperating individuals. Most often, such relatedness is caused by pedigree relationships between family members. However, an alternative explanation has recently emerged in an article by Wilson and Hölldobler (2005) . Wilson and Hölldobler see the ecological benefit of group living as the principal reason for sociality. In their scenario, individuals sharing the same altruistic allele (analogous to a greenbeard gene) preferentially interact with each other, regardless of pedigree relatedness. We argue that empirical evidence has the potential to answer the question of whether pedigree relatedness plays a role in the evolution of eusociality. We conclude that both phylogenetic studies and studies of intra-genomic conflict support the importance of pedigree relatedness in the evolution of eusociality. [ABSTRACT FROM AUTHOR]

Spatial synchrony in species abundance is a general phenomenon that has been found in populations representing virtually all major taxa. Dispersal among populations and synchronous stochastic effects (the so called "Moran effect") are the mechanisms most likely to explain such synchrony patterns. Very few studies have related the degree of spatial synchrony to the biological characteristics of species. Here we present a case where specific predictions can be made to relate river fish species characteristics and synchrony determined exclusively by a Moran effect through the expected sensitivity of species to the regional component of environmental stochasticity. By analyzing 23-year time series of abundance estimates in two isolated localities we show that species associated with synchronized reproduction during the wet season, high fecundity, small egg size and high gonado-somatic index (the so called "periodic" strategy) have a higher degree of spatial synchrony in population dynamics than species associated with the opposite traits (the so called "equilibrium" strategy). This is supported by significant relationships (P values <0.01) between species traits and the levels of synchrony after removing taxonomical relatedness. Spatial synchrony computed from summed annual total catches by groups of species, separated into strategy types also showed a significantly higher degree of synchrony for the periodic (r = 0.83) than the equilibrium (r = 0.46) group. Regional hydrological variability is likely to be partly responsible for the observed synchrony pattern and a regional discharge index showed better relationships with the periodic group, supporting the expected differential effect of regional environmental correlation on population dynamics. [ABSTRACT FROM AUTHOR]

Plant reproduction is often reduced at low densities, due to reduced pollinator visitation rates. Recent theory suggests that a disproportionate increase in pollinator visits to patches of plants as heterospecific plant density increases (i.e. if visitation is a sigmoid function of patch density) can rescue sparse populations of a focal plant species from reduced reproductive success or population decline. A field experiment was performed to determine the shape of the pollinator visitation response to patches of differing density of the common weed Brassica rapa. Both the aggregative and functional response for the entire pollinator community were saturating rather than sigmoid, indicating that pollinator response does not accelerate when density increases. The results for the entire pollinator community were consistent among temporal and spatial replicates. Aggregative response curves for specific pollinator taxa were either linear (bombyliid flies) or saturating (syrphid flies, solitary bees, and Lepidoptera). Functional responses for these taxa were saturating (syrphid flies and solitary bees) or flat (bombyliid flies and Lepidoptera). Individual pollinators visited more plants during foraging bouts in high-density patches, but visits per plant decreased. Seeds per fruit and seeds per flower increased with increasing density. There is no evidence that pollinators disproportionately visit denser patches, or that the conditions for this mechanism of pollination facilitation are likely to be met in this generalist pollinator system. [ABSTRACT FROM AUTHOR]

The terms 'habitat', 'environment' and 'niche' are used inconsistently, and with some confusion, within the ecological literature on species distribution and abundance modelling. Here I suggest interrelated working definitions of these terms whereby the concept of habitat remains associated with descriptive/correlative analyses of the environments of organisms, while the niche concept is reserved for mechanistic analyses. To model the niche mechanistically, it is necessary to understand the way an organism's morphology, physiology, and especially behaviour, determine the kinds of environment it experiences when living in a particular habitat, and it is also necessary to understand how those environmental conditions affect fitness (growth, survival and reproduction). While distributions can potentially be predicted by modelling descriptions or correlations between organisms and habitat components, we must model an organism's niche mechanistically if we are to fully explain distribution limits. A mechanistic understanding of the niche is also critical when we want to predict an organism's distribution under novel circumstances such as a species introduction or climate change. [ABSTRACT FROM AUTHOR]

Although autumn leaf colours of deciduous trees have been shown to protect against photo-oxidative damage, they are sometimes seen as signals to pests and predators. Here I modify the coevolution hypothesis of autumn leaf colours. I suggest that much of the within-population variation in autumn leaf colours can be explained by differences in the allocation of resources to sexual reproduction. According to the novel hypothesis, reproductively active woody plants produce early and intense autumn leaf colours in order to protect seeds and other reproductive tissues from pests that lay eggs in the autumn. If many seeds mature at times of leaf senescence or during the next summer, a woody plant will reallocate plenty of nitrogen to seeds. If sucking insects reproduce on such hosts, their flightless offspring will suffer poor-quality food after the ripening of seeds. Before this, however, insects will probably concentrate around the ripening seeds to forage on nitrogen-rich veins. This will decline the quality and quantity of developing seeds. If, on the other hand, insects are able to recognize reproductively active plants while laying eggs in the autumn, both the insects and the plants benefit. The flightless offspring of insects feeds on plants that supply sufficiently nitrogen for longer than reproducing plants do, while these optimise their reproduction by avoiding pests, which also contributes to the abundance of specialist pests. Hence, I suppose that while physiological factors are the origin of autumnal colour changes of deciduous leaves, the visible cue utilized by insects has evolved several times to an honest signal that reveals the unsuitability of the potential host in the near future. The reproductive insurance hypothesis may help us to understand why bright autumn leaf colours are rare among herbaceous plants, and why plants at high altitudes and latitudes are often brightly coloured in autumn. [ABSTRACT FROM AUTHOR]

The fish species vendace ( Coregonus albula) invaded the sub-arctic Pasvik watercourse during the second half of the 1980s, and became the dominant pelagic species in the upstream part of the watercourse within a few years. Life history traits of the pioneer population of vendace in Pasvik were recorded from 1991–2000. A rapid increase in population density in the upstream part of the watercourse was accompanied by decreased growth rates, decreased fecundity and a reduced size at first maturation. The downstream part of the watercourse showed a similar, but delayed, change in life history traits compared to the upstream part. The study documents great life history variability of a non-native fish species entering a new environment. We discuss two co-acting explanations for the observed patterns: (i) a density dependent response mediated by food depletion; and (ii) a pioneer strategy that allocates resources to favour reproduction at early developmental stages with a high number of offspring, trading off growth and size of offspring. [ABSTRACT FROM AUTHOR]

The members of natural populations often differ in size and relatedness to each other, which may affect the division of limited resources and have consequences on reproductive success and population dynamics. We modeled seasonal growth and dynamics in populations composed of different types of relatives (full-sibs, half-sibs and non-related individuals) under the continuum of competitive scenarios between complete symmetry and asymmetry. Growth was assumed logistic in proportion to individual biomass and the size-differences were weighted by the relatedness of individuals. The symmetric component of competition was experienced by all individuals in proportion to their biomass, whereas the asymmetric component was individual-specific, and influenced only by the individuals larger than the focal individual. Relatedness decreased and competitive asymmetry increased the variability of individual biomasses. Mortality of the smallest individuals and the size threshold of reproduction decreased population density. Population dynamics were stable when there was no size threshold for reproduction but the presence of the threshold led to cyclic dynamics under low competitive asymmetry. The effects of the threshold were greater among related than unrelated individuals. The results suggest that individual differences and the asymmetry of competition can greatly affect population dynamics. Full symmetry of competition may be evolutionarily unstable in populations of related individuals as it may increase the probability of extinction due to demographic stochasticity. [ABSTRACT FROM AUTHOR]