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In some social groups, non-breeding subordinates regulate their growth, relative to the size of their immediate dominants in ways that reduce conflict over dominance rank. We predicted that such strategic growth adjustment should also occur in breeding pairs, if this is beneficial for the more subordinate individual within a pair. Using the cichlid fish, Julidochromis transcriptus , held in a laboratory, we examined whether strategic growth regulation occurs in monogamous pairs. In female-largest pairs, smaller males grew slower than their partner when the initial size ratio of pairs (large/small) was small, but faster when the ratio was large, and the number of pairs with an intermediate size ratio increased over time. However, in male-largest pairs, smaller females had a low growth rate and the size ratio of these pairs increased over time. The most important factors for predicting the growth rate of fish were the initial size ratio of pairs for smaller males in female-largest pairs and the initial body size for larger individuals in both pair types, but no such predictors were found for smaller females in male-largest pairs. Neither feeding rate nor attacking rate of the two individuals in a pair predicted the growth rate of smaller fish in a pair. These results suggest that smaller males strategically adjust their own growth, relative to the size of their partner in female-largest pairs, wherein the growth of larger females unrestrained by social relationship with their partner can increase female fecundity, being beneficial for both sexes. The adaptive significance of a low growth rate of smaller females in male-largest pairs is also discussed. [ABSTRACT FROM AUTHOR]

Environmental temperature and body size are two prominent drivers of predation. Despite the ample evidence of their independent effects, the combined impact of temperature and predator-prey body size ratio on the strength and stability of trophic interactions is not fully understood. We experimentally tested how water temperature alters the functional response and population stability of dragonfly nymphs (Cordulegaster boltonii) feeding on freshwater amphipods (Gammarus pulex) across a gradient of their body size ratios. Attack coefficients were highest for small predators feeding on small prey at low temperatures, but shifted toward the largest predators feeding on larger prey in warmer environments. Handling time appeared to decrease with increasing predator and prey body size in the cold environment, but increase at higher temperatures. These findings indicate interactive effects of temperature and body size on functional responses. There was also a negative effect of warming on the stability of predator and prey populations, but this was counteracted by a larger predator-prey body size ratio at higher temperatures. Here, a greater Hill exponent reduced feeding at low prey densities when predators were much larger than their prey, enhancing the persistence of both predator and prey populations in the warmer environment. These experimental findings provide new mechanistic insights into the destabilizing effect of warming on trophic interactions and the key role of predator-prey body size ratios in mitigating these effects.

Body mass–based links between predator and prey are fundamental to the architecture of food webs. These links determine who eats whom across trophic levels and strongly influence the population abundance, flow of energy, and stability properties of natural communities. Body mass links scale up to create predator-prey mass relationships across species, but the origin of these relationships is unclear. Here I show that predator-prey mass relationships are consistent with the idea that body mass evolves to maximize a dependable supply of resource uptake. I used a global database of ~2,100 predator-prey links and a mechanistic optimization model to correctly predict the slope of the predator-prey mass scaling relationships across species generally and for nine taxonomic subsets. The model also predicted cross-group variation in the heights of the body mass relationships, providing an integrated explanation for mass relationships and their variation across taxa. The results suggest that natural selection on body mass at the local scale is detectable in ecological organization at the macro scale. [ABSTRACT FROM AUTHOR]

The distribution of body sizes of co-existing species at different scales reflects the scale-dependency of rules governing community assembly. Investigation of among-scale variation in community assembly is impeded by the methodological difficulties of establishing scale boundaries. Studying body size distribution in parasites allows us to avoid the problem of defining scale because parasite communities have clear boundaries and are represented by infracommunities (an assemblage harboured by an individual host), component communities (an assemblage harboured by a host population in a locality), and compound communities (an assemblage harboured by a host community in a locality). We studied body size distribution of fleas parasitic on small mammals in Western Siberia using null models. We asked whether body size ratios (i.e., size differences among coexisting species) in these communities demonstrate non-random segregated or aggregated patterns and whether these patterns differ between (a) host species, (b) host sexes and (c) infra-, component, and compound communities. No effect of host sex on the pattern of body size distribution was found at either scale, whereas an effect of host species was found in infracommunities only. We found a tendency of flea infracommunities toward segregation, whereas body size distributions in component and compound communities were consistently aggregated. We propose that the former could be caused by apparent competition (= negative indirect interactions among fleas due to shared natural enemy, i.e. a host), whereas we the latter could be explained by host- and environment-associated filtering (= factors restricting co-occurring species to a certain subset that share certain traits). We conclude that, counterintuitively, flea communities at the lowest hierarchical scale are mainly governed by evolutionary mechanisms, whereas communities at higher scale are assembled via ecological processes. [ABSTRACT FROM AUTHOR]

Abstract: Food web models parameterised using body size show promise to predict trophic interaction strengths (IS) and abundance dynamics. However, this remains to be rigorously tested in food webs beyond simple trophic modules, where indirect and intraguild interactions could be important and driven by traits other than body size. We systematically varied predator body size, guild composition and richness in microcosm insect webs and compared experimental outcomes with predictions of IS from models with allometrically scaled parameters. Body size was a strong predictor of IS in simple modules (r2 = 0.92), but with increasing complexity the predictive power decreased, with model IS being consistently overestimated. We quantify the strength of observed trophic interaction modifications, partition this into density‐mediated vs. behaviour‐mediated indirect effects and show that model shortcomings in predicting IS is related to the size of behaviour‐mediated effects. Our findings encourage development of dynamical food web models explicitly including and exploring indirect mechanisms. [ABSTRACT FROM AUTHOR]

It is well known that increasing the ambient temperature increases the metabolic rate and consequently, the foraging rate of most insects. However, temperature experienced during the immature stages of insects affects their adult size (an inverse relationship). Because body size is generally correlated to foraging success, we hypothesized that temperature indirectly influences the foraging efficiency of adult insects through developmental effects. We first investigated the role of parasitoid: host body size ratio on the handling time of Aphidius colemani (Viereck) (Hymenoptera: Braconidae), then tested the prediction that increasing temperature during immature development increases the handling time of adults. As expected, parasitoids took longer to handle large aphids than small aphids. However, large parasitoids did not have shorter handling times than small parasitoids except when attacking large (adult) aphids. Developmental temperature had the predicted effect on parasitoids: Individuals reared at 25°C were smaller than those insects reared at 15°C. Parasitoids reared at 15°C bad similar short handling times for both first instar and adult aphids, whereas parasitoids reared at 25°C took longer to handle adult aphids than first instar aphids. The size-mediated effect of temperature through development on parasitoid efficiency was opposite to the more familiar direct effect of temperature through metabolic rate. We conclude that the net effect of temperature on foraging insects will depend on its relative influence on immature and adult stages. [ABSTRACT FROM AUTHOR]

The study of female preference for male traits is of primary importance for understanding the role of sexual selection in the evolution of natural populations. Female preference is usually investigated in controlled conditions to facilitate the manipulation of variables. However, such results are rarely confirmed in wild populations where many variables act together. Inferring the role of female preference in the outcome of reproduction thus requires field studies and a specific approach to behavioural data. We observed, over 2 years, the courtship behaviours of male and female brown trout in six populations distributed along a French watershed. We focused on behavioural items linked to female preference for male body size. We built a behavioural model describing the relationships between behaviour and female preference and estimated the parameters of the model using a Bayesian modelling approach. We found a significant preference for body size ratio: females tended to prefer males at least 1.45 times their own size. This preference varied between populations and was influenced by female size. Operational sex ratio had only a weak influence on female preference. Our model explained 44% of the observed variation in behaviour. Finally, because observed body size ratio at mating was generally greater than 1, we conclude that female preference plays a major role in the outcome of reproduction in wild populations of brown trout. These results are compared with existing knowledge and theory and their possible consequences at the population level are discussed. [Copyright &y& Elsevier]

Trophic information—who eats whom—and species' body sizes are two of the most basic descriptions necessary to understand community structure as well as ecological and evolutionary dynamics. Consumer-resource body size ratios between predators and their prey, and parasitoids and their hosts, have recently gained increasing attention due to their important implications for species' interaction strengths and dynamical population stability. This data set documents body sizes of consumers and their resources. We gathered body size data for the food webs of Skipwith Pond, a parasitoid community of grass-feeding chalcid wasps in British grasslands; the pelagic community of the Benguela system, a source web based on broom in the United Kingdom; Broadstone Stream, UK; the Grand Cariçaie marsh at Lake Neuchâtel, Switzerland; Tuesday Lake, USA; alpine lakes in the Sierra Nevada of California; Mill Stream, UK; and the eastern Weddell Sea Shelf, Antarctica. Further consumer-resource body size data are included for planktonic predators, predatory nematodes, parasitoids, marine fish predators, freshwater invertebrates, Australian terrestrial consumers, and aphid parasitoids. Containing 16 807 records, this is the largest data set ever compiled for body sizes of consumers and their resources. In addition to body sizes, the data set includes information on consumer and resource taxonomy, the geographic location of the study, the habitat studied, the type of the feeding interaction (e.g., predacious, parasitic) and the metabolic categories of the species (e.g., invertebrate, ectotherm vertebrate). The present data set was gathered with the intent to stimulate research on effects of consumer-resource body size patterns on food-web structure, interaction-strength distributions, population dynamics, and community stability. The use of a common data set may facilitate cross-study comparisons and understanding of the relationships between different scientific approaches and models. [ABSTRACT FROM AUTHOR]