Andrew Sih

• Professor
• University of California, Davis

Anthropogenic change forces animals to navigate novel conditions, including evolutionary traps formed by decoupling cues from their previously evolved meaning. One underexplored feature that could drive variation in response to traps is social context. We looked at how group size influences the behaviour of western mosquitofish, Gambusia affinis, g...

Home ranges (HRs), the regions within which animals interact with their environment, constitute a fundamental aspect of their ecology. HR sizes and locations commonly reflect costs and benefits associated with diverse social, biotic, and abiotic factors. Less is known, however, about how these factors affect intraspecific variation in HR size or fi...

Rapid environmental change is affecting many organisms; some are coping well but many species are in decline. A key mechanism for facilitating success following environmental change is phenotypic plasticity. Organisms use cues to respond phenotypically to environmental conditions; many incorporate recent information (within-generation plasticity) a...

Rapid environmental change can affect both the mean and variability in environmental conditions. Natural selection tends to favour those organisms that best respond to such changes. Here, we consider delayed germination as bet hedging strategies for 10 Sonoran Desert annuals. We use a germination model parameterized with long-term demographic and c...

Individual variation in movement is profoundly important for fitness and offers key insights into the spatial and temporal dynamics of populations and communities. Nonetheless, individual variation in fine‐scale movement behaviours is rarely examined even though animal tracking devices offer the long‐term, high‐resolution, repeatable data in natura...

Following rapid environmental change, why do some animals thrive, while others struggle? We present an expanded, cue–response framework for predicting variation in behavioral responses to novel situations. We show how signal detection theory can be used when individuals have three behavioral options (approach, avoid, or ignore). Based on this theor...

Many plant species worldwide are dispersed by scatter-hoarding granivores: animals that hide seeds in numerous, small caches for future consumption. Yet, the evolution of scatter-hoarding is difficult to explain because undefended caches are at high risk of pilferage. Previous models have attempted to solve this problem by giving cache owners large...

Within populations, individuals often differ consistently in their average level of behavior (i.e., animal personality), as well as their response to environmental change (i.e., behavioral plasticity). Thus, changes in environmental conditions might be expected to mediate the structure of animal personality traits. However, it is currently not well...

Interview with Andrew Sih, who studies the evolution and ecological impacts of behavior on population patterns at the University of California, Davis.

Natal dispersal plays an important role in connecting individual animal behavior with ecological processes at all levels of biological organization. As urban environments are rapidly increasing in extent and intensity, understanding how urbanization influences these long distance movements is critical for predicting the persistence of species and c...

The social niche hypothesis theorizes that repeated social interactions between group members is an important mechanism for generating consistent individual differences in behaviour. However, such frequent interactions also have the potential to mask or suppress behavioural differences if individuals conform towards a group behavioural norm (i.e. t...

This article has been retracted. Please see the Retraction Notice for more detail: https://doi.org/10.1007/s00265-021-02997-3

Despite growing attention to the ecological and evolutionary importance of consistent individual differences in behaviour (animal personality), long-term field studies quantifying factors associated with behavioural repeatability remain rare. Here, we studied animal personalities over an 8-year period, representing 6 study years, in a wild populati...

Ecologists have long been interested in linking individual behaviour with higher level processes. For motile species, this ‘upscaling’ is governed by how well any given movement strategy maximizes encounters with positive factors and minimizes encounters with negative factors. Despite the importance of encounter events for a broad range of ecologic...

Studies of eusocial insects have extensively investigated two components of task allocation: how individuals distribute themselves among different tasks in a colony and how the distribution of labor changes to meet fluctuating task demand. While discrete age- and morphologically-based task allocation systems explain much of the social order in thes...

While a large body of research has focused on the physiological effects of multiple environmental stressors, behavioral effects remain far less studied. However, behavioural plasticity can not only directly drive responses to stressors but can also mediate physiological responses. Here, we provide a conceptual framework incorporating four fundament...

Understanding why some individuals are more prone to carry parasites and spread diseases than others is a key question in biology. Although epidemiologists and disease ecologists increasingly recognize that individuals of the same species can vary tremendously in their relative contributions to the emergence of diseases, very few empirical studies...

Successful invasive species are often closely related to other invasive species, suggesting that shared traits contribute to their invasion success. Alternatively, related species can differ in invasiveness, where some are highly invasive yet congeners seem unable to invade. Here, we compared the traits and establishment abilities of two highly suc...

We provide an overview on the study of animal personalities that have now been documented in a broad range of animal taxa. We define the concept of an animal personality, the related idea of a behavior syndrome, how these are quantified by animal behaviorists, and clarify common misconceptions about these concepts. We then discuss several issues th...

We provide an overview on the study of animal personalities that have now been documented in a broad range of animal taxa. We define the concept of an animal personality, the related idea of a behavior syndrome, how these are quantified by animal behaviorists, and clarify common misconceptions about these concepts. We then discuss several issues th...

The very presence of predators can strongly influence flexible prey traits such as behavior, morphology, life history, and physiology. In a rapidly growing body of literature representing diverse ecological systems, these trait (or “fear”) responses have been shown to influence prey fitness components and density, and to have indirect effects on ot...

Enemy‐risk effects, often referred to as non‐consumptive effects (NCEs), are an important feature of predator–prey ecology, but their significance has had little impact on the conceptual underpinning or practice of biological control. We provide an overview of enemy‐risk effects in predator–prey interactions, discuss ways in which risk effects may...

Managing vertebrate pests is a global conservation challenge given their undesirable socio-ecological impacts. Pest management often focuses on the 'average' individual, neglecting individual-level behavioural variation ('personalities') and differences in life histories. These differences affect pest impacts and modify attraction to, or avoidance...

1. Ecologists have long been interested in linking individual behavior with higher-level processes. For motile species, this 'upscaling' is governed by how well any given movement strategy maximizes encounters with positive factors, and minimizes encounters with negative factors. Despite the importance of encounter events for a broad range of ecolo...

The snake mite, Ophionyssus natricis (Acari: Macronyssidae), occurs in many parts of the world and is of animal and human health significance. In Australia Op. natricis is considered an introduced species in parts of coastal eastern and southern Australia and is thought to be absent in the wild. Herein we report on the occurrence of Op. natricis in...

The risk of consumption is a pervasive aspect of ecology and recent work has focused on synthesis of consumer–resource interactions (e.g., enemy–victim ecology). Despite this, theories pertaining to the timing and magnitude of defenses in animals and plants have largely developed independently. However, both animals and plants share the common dile...

Consistent individual tendencies in behaviour, or behavioural types, are likely to impact the dynamics and outcomes of animal‐mediated seed dispersal. We review the extant literature on this issue and outline a conceptual overview to guide this emerging field. We provide an overview of possible ways in which behavioural types can affect animal‐medi...

Consistent individual differences in behavior [i.e., behavioral types (BTs)], are common across the animal kingdom. Consistency can make behavior an adaptive trait for mate choice decisions. Here, we present a conceptual framework to explain how and why females might evaluate a male’s BT before mating. Because BTs are consistent across time or cont...

A key challenge in invasion biology is identifying characteristics that allow some species to be repeatedly successful at invading novel environments. Invasions can often be disproportionately driven by a single sex, with differences in behavioural mechanisms between the sexes potentially underlying sex-biased invasiveness. Here, we took an animal...

Individual hosts vary substantially in their parasite loads. However, whether individual hosts have consistently different loads remains uncertain. If so, hosts that have consistently high parasite loads may serve as key reservoirs or super‐spreaders. Thus, identifying whether individuals persistently differ in their parasitism and the factors that...

How an invader responds to the novel biotic elements of a new community will affect its ability to invade. Species that are able to cope well with novel competitors might be expected to achieve greater establishment success. We compared the population-level responses of two mosquitofish species, the widespread invader Gambusia affinis and non-invas...

Increased turbidity, a common human-induced aquatic disturbance, can potentially have major impacts on predator–prey interactions via effects on key foraging and antipredator behaviours, on the repeatability of these behaviours (i.e. on animal personalities) and on behavioural syndromes (correlations among behaviours). Here, we repeatedly assayed i...

Predators and prey are often engaged in a game where their expected fitnesses are affected by their relative spatial distributions. Game models generally predict that when predators and prey move at similar temporal and spatial scales that predators should distribute themselves to match the distribution of the prey's resources and that prey should...

Our ability to predict how species will respond to human-induced rapid environmental change (HIREC) may depend upon our understanding of transgenerational plasticity (TGP), which occurs when environments experienced by previous generations influence phenotypes of subsequent generations. TGP evolved to help organisms cope with environmental stressor...

Many animals respond well behaviorally to stimuli associated with human-induced rapid environmental change (HIREC), such as novel predators or food sources. Yet others make errors and succumb to evolutionary traps: approaching or even preferring low quality, dangerous or toxic options, avoiding beneficial stimuli, or wasting resources responding to...

Mosquitofish (Gambusia affinis) are a widespread, invasive species that frequently colonize habitats where they might encounter novel predators. Earlier work showed that asocial mosquitofish disperse more readily than social fish. Initial colonists to newly invaded, low density sites should thus be relatively asocial. Here, we tested the hypothesis...

Many plant species worldwide are dispersed by scatterhoarding granivores: animals that hide seeds in numerous, small caches for future consumption. Yet, the evolution of scatterhoarding is difficult to explain because undefended caches are at high risk of pilferage. Previous models have attempted to solve this problem by giving cache owners unreali...

A major focus of research in behavioural ecology involves testing whether behaviour, on average, is adaptive. Here, we note that although studies often find that individuals differ in how well they perform adaptive behaviour (e.g. some individuals fit the predictions of optimal diet theory better than others, and some exhibit higher social skill th...

Animal mating systems are often studied with the goal of understanding why species, populations, or groups vary from one another in the system they display. Although these differences are often treated as basically stable, it is also known that mating systems may shift over time (e.g., from one breeding season to the next). There has been some stud...

Laboratory measurements of physiological and demographic tolerances are important in understanding the impact of climate change on species diversity; however, it has been recognized that forecasts based solely on these laboratory estimates overestimate risk by omitting the capacity for species to utilize microclimatic variation via behavioral adjus...

Human-induced rapid environmental change (HIREC) poses threats to a variety of species, and if or how it changes phenotypes is a question of central importance bridging evolutionary ecology and conservation management. Social learning is one type of phenotypic plasticity that can shape organismal responses to HIREC; it allows organisms to acquire p...

Human-induced rapid environmental change (HIREC) has recently led to alterations in the fitness and behavior of many organisms. Game theory is an important tool of behavioral ecology for analyzing evolutionary situations involving multiple individuals. However, game theory bypasses the details by which behavioral phenotypes are determined, taking t...

Largemouth Bass (Micropterus salmoides) were introduced into the Sacramento-San Joaquin Delta (the Delta) over 100 years ago. In the last 2 decades, the abundance of centrarchids (including Largemouth Bass) in the littoral zone has increased, while some native fish and fish that were previously abundant in the pelagic zone have declined. Largemouth...

Decisions made while searching for settlement sites (e.g., nesting, oviposition) often have major fitness implications. Despite numerous case studies, we lack theory to explain why some species are thriving while others are making poor habitat choices after environmental change. We develop a model to predict (1) which kinds of environmental change...

Arguments for the need to conserve aquatic predator (AP) populations often focus on the ecological and socioeconomic roles they play. Here, we summarize the diverse ecosystem functions and services connected to APs, including regulating food webs, cycling nutrients, engineering habitats, transmitting diseases/parasites, mediating ecological invasio...

Climate change induced phenological variation in amphibians can disrupt time-sensitive processes such as breeding, hatching, and metamorphosis, and can consequently alter size-dependent interactions such as predation. Temperature can further alter size-dependent, predator-prey relationships through changes in species’ behavior. We thus hypothesized...

Exotic predators can have major negative impacts on prey. Importantly, prey vary considerably in their behavioral responses to exotic predators. Factors proposed to explain variation in prey response to exotic predators include the similarity of new predators to familiar, native predators, the prevalence and diversity of predators in a prey’s past,...

For many decades, researchers have studied how plants use bet-hedging strategies to insure against unpredictable, unfavourable conditions. We improve upon earlier analyses by explicitly accounting for how variable precipitation affects annual plant species' bet-hedging strategies. We consider how the survival rates of dormant seeds (in a 'seed bank...

In recent decades, pyrethroid pesticides have been deemed a safer alternative to previously used pesticides. While some evidence supports this assumption in mammals and birds, exposure to certain pyrethroids can affect concentrations of hormones vital to reproduction in fish. Thus, we hypothesized that pyrethroid exposure impacts fish reproductive...

For many decades, researchers have studied how plants use bet-hedging strategies to insure against unpredictable, unfavorable conditions. We improve upon earlier analyses by explicitly accounting for how variable precipitation affects annual plant species’ bet-hedging strategies. We consider how the survival rates of dormant seeds (in a ‘seed bank’...

A suite of submersed aquatic vegetation (SAV) species, and especially Brazilian Waterweed (Egeria densa), has proliferated rapidly in California's Sacramento-San Joaquin Delta. This expansion is concurrent with population declines in native fish species and increases in many non-native fish species, including Largemouth Bass Micropterus salmoides....

Human-induced rapid environmental change (HIREC) has recently led to alterations in the fitness and behavior of many organisms. Game theory is an important tool of behavioral ecology for analyzing evolutionary situations involving multiple individuals. However, game theory bypasses the details by which behavioral phenotypes are determined, taking t...

Chemical contaminants (e.g. metals, pesticides, pharmaceuticals) are changing ecosystems via effects on wildlife. Indeed, recent work explicitly performed under environmentally realistic conditions reveals that chemical contaminants can have both direct and indirect effects at multiple levels of organization by influencing animal behaviour. Altered...

Movement is often used to indicate host vigour, as it has various ecological and evolutionary implications, and has been shown to be affected by parasites. We investigate the relationship between tick load and movement in the Australian Sleepy Lizard (Tiliqua rugosa (Gray, 1825)) using high resolution GPS tracking. This allowed us to track individu...

California’s coastal ecosystems are forecasted to undergo shifting ocean conditions due to climate change, some of which may negatively impact recreational and commercial fish populations. To understand if fish populations have the capacity to respond to multiple stressors, it is critical to examine interactive effects across multiple biological sc...

Many animals socialize in two or more major ecological contexts. In nature, these contexts often involve one situation in which space is more constrained (e.g. shared refuges, sleeping cliffs, nests, dens or burrows) and another situation in which animal movements are relatively free (e.g. in open spaces lacking architectural constraints). Although...

To test the hypothesis that male harassment of females reduces adult female time spent on the water foraging (water use), and thus cannibalism by adult females on juveniles, we manipulated heterospecific prey availability, and social context in adult water striders and measured their effects on: 1) cannibalism of juveniles, 2) activity of adults an...

Estuaries are highly variable environments where fish are subjected to a diverse suite of habitat features (e.g., water quality gradients, physical structure) that filter local assemblages from a broader, regional species pool. Tidal, climatological, and oceanographic phenomena drive water quality gradients and, ultimately, expose individuals to ot...

When individual animals make decisions, they routinely use information produced intentionally or unintentionally by other individuals. Despite its prevalence and established fitness consequences, the effects of such social information on ecological dynamics remain poorly understood. Here, we synthesize results from ecology, evolutionary biology, an...

Turbidity (a measure of the cloudiness of water) decreases the visual range of organisms, altering interactions within and between species. For species that visually assess mates, turbidity may affect mating interactions and mate choice. A central question, then, is to what degree organisms plastically adjust mating behaviors to cope with visually...

Behaviour is a key interface between an animal's genome and its environment. Repeatable individual differences in behaviour have been extensively documented in animals, but the molecular underpinnings of behavioural variation among individuals within natural populations remain largely unknown. Here, we offer a critical review of when molecular tech...

Social network analyses allow researchers to describe patterns of social interactions and their consequences in animal societies. Since direct observations in natural settings are often difficult, researchers often use tracking technologies to build proximity-based social networks. However, because both social behaviour (e.g. conspecific attraction...

Signal detection theory has influenced the behavioural sciences for over 50 years. The theory provides a simple equation that indicates numerous ‘intuitive’ results; e.g. prey should be more prone to take evasive action (in response to an ambiguous cue) if predators are more common. Here, we use analytical and computational models to show that, in...

We describe a conceptual framework integrating animal personalities, movement ecology, social networks and parasite transmission. For directly transmitted parasites, parasite transmission depends on social interaction patterns that can be quantified using social network metrics. For indirectly transmitted parasites, the key can be transmission netw...

Dispersers are often not a random draw from a population, dispersal propensity being conditional on individual phenotypic traits and local contexts. This non‐randomness consequently results in phenotypic differences between dispersers and non‐dispersers and, in the context of biological invasions, in an invasion front made of individuals with a bia...

Mating systems can vary within-species but the environmental drivers and behavioral mechanisms underlying this variation are seldom investigated experimentally. We experimentally assessed how individual behavioral plasticity in response to changes in pool and group size resulted in fundamental shifts in mating systems in water striders. We observed...

We report on 35. years of research into behavior and ecology of the Australian sleepy lizard, Tiliqua rugosa. We describe the unusually long monogamous pairing period in this lizard before mating takes place each spring, and the long-term persistence of mating pairs, reforming each spring for up to 27. years. We review hypotheses, observations, and...

Change in behaviour is usually the first response to human‐induced environmental change and key for determining whether a species adapts to environmental change or becomes maladapted. Thus, understanding the behavioural response to human‐induced changes is crucial in the interplay between ecology, evolution, conservation and management. Yet the beh...

Human activity alters natural habitats for many species. Understanding variation in animals’ behavioural responses to these changing environments is critical.We showhowsignal detection theory can be used within awider framework of state-dependent modelling to predict behavioural responses to a major environmental change: novel, exotic species. We a...

Recent studies have established the ecological and evolutionary importance of animal personalities. Individual differences in movement and space-use, fundamental to many personality traits (e.g. activity, boldness and exploratory behaviour) have been documented across many species and contexts, for instance personality-dependent dispersal syndromes...

Trait-based ecology argues that an understanding of the traits of interactors can enhance the predictability of ecological outcomes. We examine here whether the multidimensional behavioural-trait diversity of communities influences community performance and stability in situ. We created experimental communities of web-building spiders, each with an...

Although animals vary substantially in their behavioral responses to human-induced rapid environmental change (HIREC), we are only beginning to develop theory to explain this variation. Signal detection theory predicts variation in responses to novel dangerous organisms (exotic predators or toxic prey) or exotic organisms that are safe but might ap...

Despite a central line of research aimed at quantifying relationships between mating success and sexually dimorphic traits (e.g., ornaments), individual variation in sexually selected traits often explains only a modest portion of the variation in mating success. Another line of research suggests that a significant portion of the variation in matin...

It is well established that parasites can have profound effects on the behaviour of host organisms, and that individual differences in behaviour can influence susceptibility to parasite infections. Recently, two major themes of research have developed. First, there has been a growing interest in the proximate, mechanistic processes underpinning par...

Frequent invasions in coastal ecosystems result in novel species interactions that have unknown ecological consequences. Largemouth Bass Micropterus salmoides and Brazilian waterweed Egeria densa are introduced species in the Sacramento–San Joaquin River Delta (the Delta) of California, a highly modified estuary. In this system, Brazilian waterweed...

Understanding how animals interact with their physical and social environment is a major question in ecology, but separating between these factors is often challenging. Observed interaction rates may reflect social behaviour – preferences or avoidance of conspecifics or certain phenotypes. Yet, environmental spatiotemporal heterogeneity also affect...

Social structure is a fundamental component of a population that drives ecological and evolutionary processes ranging from parasite transmission to sexual selection. Nevertheless, we have much to learn about factors that explain variation in social structure. We used advances in biologging and social network analysis to experimentally test how the...

This study validated a technique for non-invasive hormone measurements in California killifish Fundulus parvipinnis, and looked for associations between cortisol (a stress hormone) and 11-ketotestosterone (KT, an androgen) release rates and the density or intensity of the trematode parasites Euhaplorchis californiensis (EUHA) and Renicola buchanani...

Behavioral hyper volumes vs. mass gain for each species

Dissimilarities and individual mass gains

Model comparisons via AIC

Repeatability and behavioral correlation

Behavioral hyper volumes vs. mass gain for each species

Repeatability and behavioral correlation

Tests for associations between personality and starting body mass

Tests for associations between personality and starting body mass

Dissimilarities and individual mass gains

Model comparisons via AIC