Are scared prey as good as dead?

Predators affect prey and their resources by changing the density and traits (e.g. morphology and behavior) of those prey. Ecological studies and models of community dynamics, however, typically only incorporate how changes in prey densities, rather than their traits, affect community dynamics. In a recent meta-analysis, Preisser et al. show that trait effects are as large, if not larger than density effects. This strongly suggests that trait effects should be integrated into empirical and theoretical studies.     

Female mate assessment and choice behavior affect the frequency of alternative male mating tactics

Explanations for the existence of alternative male mating tacticsfocus primarily on male–male competition. Mating systems,however, are composed of interactions both within and betweenthe sexes, and the role of female behavior in shaping male matingtactics should not be overlooked. By using a dynamic state variablegame model, I examine how female mate assessment and choicebehavior affect the frequency of alternative male mating tactics.When females can accurately assess the quality of males, onlymales with high quality are likely to be chosen as mates, andthus, lower-quality males gain little fitness from courtingfemales. This leads lower-quality males to switch to an alternativemating tactic that attempts to circumvent female mate choice.In contrast, if the abilities of females to accurately assessmales are constrained by assessment costs, imperfect information,or time constraints, or if the pool of available males is smaller,then lower-quality males are increasingly chosen as mates andthey less often use alternative mating tactics. Thus, femalebehavior shapes the frequency of alternative male mating tactics.A consequence of this game between the sexes is that male behavior(i.e., increased alternative mating tactics) decreases the benefitsfemales might otherwise gain from lower assessment costs, clearersignals of male quality, more time to choose a male, and moremales from which to choose a mate.     

State-Dependent Mate-Assessment and Mate-Selection Behavior in Female Threespine Sticklebacks (Gasterosteus aculeatus, Gasterosteiformes: Gasterosteidae)

Most investigations of mate-choice have focused on the outcomes of mate-choice (i.e. which mates are chosen), and thus we generally know very little about how mates are chosen (i.e. how mates are found, assessed, and selected). Mate-choice by females has been shown to be dependent on the state of the female, with females being less selective when limited by time or energy. This result could be caused by changes in female mate-assessment or mate-selection behavior. We examined whether manipulations of time and energy affected the mate-choice behavior of female threespine stickleback ( Gasterosteus aculeatus ). We found that female mate-choice behavior, when not divided into stages, was affected by both of the manipulations. This matches previous findings. When we divided female courtship behavior into six stages, we found that the two manipulations affected different portions of the mate-choice process. The holding-time manipulation changed female behavior at the beginning and end of the mate-choice process and the swimming manipulation changed female behavior only at the end of the mate-choice process. Neither of the manipulations significantly affected female behavior in the middle portion of the mate-choice process. Thus, the mate-choice process appears to be composed of multiple state-dependent decisions. We discuss how a better mechanistic understanding of how female state affects female mate-choice behavior can produce testable predictions and provide a basis for investigating the evolution of mating systems.     

Comparing alternative models to empirical data: cognitive models of western scrub-jay foraging behavior

Animals often select one item from a set of candidates, as when choosing a foraging site or mate, and are expected to possess accurate and efficient rules for acquiring information and making decisions. Little is known, however, about the decision rules animals use. We compare patterns of information sampling by western scrub-jays (Aphelocoma californica) when choosing a nut with three decision rules: best of n (BN), flexible threshold (FT), and comparative Bayes (CB). First, we use a null hypothesis testing approach and find that the CB decision rule, in which individuals use past experiences to make nonrandom assessment and choice decisions, produces patterns of behavior that more closely correspond to observed patterns of nut sampling in scrub-jays than the other two rules. This approach does not allow us to quantify how much better CB is at predicting scrub-jay behavior than the other decision rules. Second, we use a model selection approach that uses Akaike Information Criteria to quantify how well alternative models approximate observed data. We find that the CB rule is much more likely to produce the observed patterns of scrub-jay behavior than the other rules. This result provides some of the best empirical evidence of the use of Bayesian information updating by a nonhuman animal.     

Environmental tolerance, heterogeneity, and the evolution of reversible plastic responses

Phenotypic plasticity is a key factor for the success of organisms in heterogeneous environments. Although many forms of phenotypic plasticity can be induced and retracted repeatedly, few extant models have analyzed conditions for the evolution of reversible plasticity. We present a general model of reversible plasticity to examine how plastic shifts in the mode and breadth of environmental tolerance functions (that determine relative fitness) depend on time lags in response to environmental change, the pattern of individual exposure to inducing and noninducing environments, and the quality of available information about the environment. We couched the model in terms of prey-induced responses to variable predation regimes. With longer response lags relative to the rate of environmental change, the modes of tolerance functions in both the presence or absence of predators converge on a generalist strategy that lies intermediate between the optimal functions for the two environments in the absence of response lags. Incomplete information about the level of predation risk in inducing environments causes prey to have broader tolerance functions even at the cost of reduced maximal fitness. We give a detailed analysis of how these factors and interactions among them select for joint patterns of mode and breadth plasticity.     

Resource Selection by Recolonizing American Black Bears

American black bears (Ursus americanus) were extirpated from Oklahoma, USA, in the early twentieth century but have since recolonized eastern portions of the state after immigrating from Arkansas, where they were successfully translocated. Within the last 2 decades, a population of black bears was detected in the Oklahoma Ozark region, prompting studies to determine population size, growth rate, and genetic makeup. To understand how black bears were recolonizing the human-dominated landscape, we investigated resource selection at 2 scales. Between 2011 and 2016, we collected global positioning system collar spatial data for 10 males and 13 females. We calculated average kernel density home ranges on a seasonal scale for all collared bears. We used generalized linear mixed models to calculate resource selection functions at the study area, defined by locations of all radio-collared black bears (second order) and the scale of individual black bear home ranges (third order). Resource selection did not differ significantly by sex. Black bears across seasons and scales selected riparian forest and moist oak (Quercus spp.) forest land cover types and mostly selected against indicators of human activity (e.g., pasture-prairie, anthropogenic land cover types, roads, and areas of high human population density). Black bears also selected areas with rugged terrain at high elevations, although not consistently across seasons and scales. Black bear recolonization appeared to be negatively affected by areas and features characterized as human-altered. Further expansion of the range of black bears may be limited by anthropogenic disturbance in the region. © 2021 The Wildlife Society.     

A Comparative Bayes tactic for mate assessment and choice

Models of mate choice tactics have assumed that females randomlyencounter males when collecting information and the informationis perfect. Empirical observations of four bird species showthat females selectively visit males and repeat visits to malesbefore mating. This suggests that the assumptions of previousmodels have been too restrictive. An alternative model of informationgathering and mate choice, which relaxes the assumptions ofrandom encounters and perfect information, is presented. Inthis Comparative Bayes model, the decision of when and fromwhom to collect information is made using Bayesian estimatesof each male's quality. Predictions from the model are that:(1) the occurrence of mate assessment will increase as initialuncertainty about the quality of males increases, as the costof gathering information decreases, and as the signal perceivedby the female becomes a better representation of males' actualqualities; (2) the occurrence of repeat visits to males willbe highest when signals from males are of medium reliability;and (3) the decision of which male to assess will depend onthe estimated qualities of males, prior certainty about eachmale's quality, the reliability of each male's signal, and thecosts of assessment. Simulations compare the fitness outcomesof the Comparative Bayes tactic to other mate choice tactics.The fitness from the Comparative Bayes tactic is significantlyhigher than from the fixed threshold tactic and than from thebest-of-n tactic when the cost of assessment is low. [BehavEcol 7: 451–460 (1996)]     

Risk, resources and state-dependent adaptive behavioural syndromes

Many animals exhibit behavioural syndromes-consistent individual differences in behaviour across two or more contexts or situations. Here, we present adaptive, state-dependent mathematical models for analysing issues about behavioural syndromes. We find that asset protection (where individuals with more 'assets' tend be more cautious) and starvation avoidance, two state-dependent mechanisms, can explain short-term behavioural consistency, but not long-term stable behavioural types (BTs). These negative-feedback mechanisms tend to produce convergence in state and behaviour over time. In contrast, a positive-feedback mechanism, state-dependent safety (where individuals with higher energy reserves, size, condition or vigour are better at coping with predators), can explain stable differences in personality over the long term. The relative importance of negative- and positive-feedback mechanisms in governing behavioural consistency depends on environmental conditions (predation risk and resource availability). Behavioural syndromes emerge more readily in conditions of intermediate ecological favourability (e.g. medium risk and medium resources, or high risk and resources, or low risk and resources). Under these conditions, individuals with higher initial state maintain a tendency to be bolder than individuals that start with low initial state; i.e. later BT is determined by state during an early 'developmental window'. In contrast, when conditions are highly favourable (low risk, high resources) or highly unfavourable (high risk, low resources), individuals converge to be all relatively bold or all relatively cautious, respectively. In those circumstances, initial differences in BT are not maintained over the long term, and there is no early developmental window where initial state governs later BT. The exact range of ecological conditions favouring behavioural syndromes depends also on the strength of state-dependent safety.     

Alternative statistical approaches to the use of data as evidence for hypotheses in human behavioral ecology

In their ambitious Evolutionary Anthropology paper, Winterhalder and Smith 1 review the history, theory, and methods of human behavioral ecology (HBE). In establishing how HBE differs from traditional approaches within sociocultural anthropology, they and others laud its hypothetical‐deductive research method. 1 - 3 Our aim is to critically examine how human behavioral ecologists conduct their research, specifically how they analyze and interpret data as evidence for scientific hypotheses. Through computer simulations and a review of empirical studies of human sex ratios, we consider some limitations of the status quo and present alternatives that could strengthen the field. In particular, we suggest that because human behavioral ecologists often consider multiple hypotheses, they should use statistical approaches that can quantify the evidence in empirical data for competing hypotheses. Although we focus on HBE, the principles of this paper apply broadly within biological anthropology.     

Relative strengths of trait-mediated and density-mediated indirect effects of a predator vary with resource levels in a freshwater food chain

Predators can affect the density and traits (e.g. morphology, behavior) of their prey, and either change may influence how prey interact with their resources. Thus, predators can interact indirectly with resource species (i.e. two trophic levels below) through two separate mechanisms. The relative strengths of these two kinds of indirect effects have rarely been compared directly, and how their relative importance varies across environmental gradients is virtually unknown. We investigated the relative strength of trait- and density-mediated indirect effects of the predatory insect Belostoma flumineum on algal communities through predation on the pond snail, Physa gyrina , across a gradient of basal resource abundance. Because prey balance the benefits of foraging against the increased risk of predation while foraging, the availability of the prey's resource should influence the strength of anti-predator behavioral responses and hence the strength of trait-mediated indirect interactions. Belostoma presence had positive indirect effects on resources as expected and total predator effects were constant across the basal resource gradient. At low initial resource levels, trait-mediated indirect effects on algal biomass exceeded density-mediated indirect effects, while at high initial resources the reverse was true. Snails showed similar habitat use across the resource gradient suggesting that the anti-predator response was most likely a depression of activity levels.