Habitat-specific Predation Risk Research Articles

Axes of fear for stream fish: water depth and distance to cover

To better understand habitat-specific predation risk for stream fish, we used an approach that assumes animals trade off food for safety and accurately assess risk such that predation risk can be measured as a foraging cost: animals demand greater harvest rates to occupy riskier locations. We measured the foraging cost of predation risk for juvenile salmonids within enclosures in a natural stream at locations that varied in water depth and distance to cover. Measurements relied on a food delivery apparatus and direct observations that allowed estimation of “giving-up” harvest rates – food delivery rates at which animals left the feeding apparatus. Juvenile steelhead about 120 mm fork length exhibited sharp increases in giving-up harvest rate with decreasing water depth and refused to use the feeding device even when offered extreme food delivery rates in water ≤20 cm deep. Giving-up harvest rates were less affected by the distance to cover. Assuming the gradients we observed in giving-up harvest rates reflect predation risk, the results of this study can be applied to spatially explicit models of stream fish populations that incorporate risk into both habitat selection and mortality due to predation.

Predation as a Determinant of Minimum Group Size in Baboons

Predation risk places a pressure on animals to adopt mechanisms by which they reduce their individual risk of being preyed on. However, a consensus on methods of determining predation risk has yet to be reached. One of the most widespread ways in which animals respond to predation risk is by living in groups. Minimum permissible group size is the smallest group size that animals are able to live in, given the habitat-specific predation risk they face. We explore ways in which predation risk can be measured and analyse its effect on minimum observed group size in baboons. Using data on predator density, habitat composition and baboon body size, we investigate the impact of the components of predation risk on baboon group size, and derive an equation that best predicts minimum group size. Minimum group size in baboons is related to predator density and female body mass. Both of these elements can, in turn, be estimated from environmental variables. These findings present support for the argument that group living in primates is a response to predation risk and offer potentially new ways of investigating carnivore and primate ecology.

California spiny lobster (Panulirus interruptus) movement behaviour and habitat use: implications for the effectiveness of marine protected areas

The effectiveness of conservation efforts, including marine protected areas (MPAs), hinges on adequate knowledge of movement patterns, habitat associations and habitat-specific survival rates of mobile organisms. California spiny lobsters (Panulirus interruptus) support commercial and recreational fishing in southern California; however, we lack basic information to determine whether MPAs planned for the region will enhance abundance. Working within and outside a small southern California MPA, we (1) quantified the movement patterns and home ranges of the lobster over two time scales, (2) determined lobster day and night habitat associations and (3) determined habitat-specific predation risk. Lobsters exhibited high site fidelity and small home ranges (geometric mean of 651 m2 and 5912 m2 per week, on the basis of 50% and 95% kernel utilisation distributions, respectively). Lobsters were associated with rocky habitat during the day and with the red algae Plocamium cartilagineum while feeding at night. Relative survival rates of lobsters were high across vegetated and unvegetated habitats at night, and were highest in surfgrass (Phyllopsadix torreyi) habitat during the day. Our results highlight the need to consider how movement patterns vary over short and long time scales, and how habitat use may vary from day to night for nocturnally active species such as lobsters, when planning MPAs.

Vigilance and predation of a forest-living bird species depend on large-scale habitat structure

Prey often use visual cues to detect predators, and consequently, many studies have assessed the effect of small-scale habitat structure on prey antipredator vigilance. This scale may be inappropriate to assess the link between habitat structure and vigilance, however, because visually hunting predators often detect prey from several hundred meters away. As a result, largescale habitat structure could affect both the hunting decisions of predators and antipredator behaviors of prey. Here we investigated the effect of small- and large-scale habitat structure, as well as group composition (kinship) on vigilance allocation of breeders in the Siberian jay Perisoreus infaustus. Vigilance had an antipredator function and was increased after exposure to a predator model. Small-scale habitat structure did not affect vigilance rates, however, habitat structure of the whole territory, measured as the proportion of visual cover, affected vigilance depending on group composition. Breeders with retained offspring (kin) in their group were more vigilant in managed open territories than on pristine dense territories, whereas breeders without kin in their groups did not adjust vigilance rates in relation to large-scaled habitat structure. Earlier studies have revealed that hawks, the main predators of jays, primarily kill non-kin group members living in groups inhabiting open territories. Therefore, we suggest that breeders adjusted their vigilance depending on the habitat-specific predation risk to protect their retained offspring. This demonstrates that large-scale habitat structure affects predator‐prey interactions and is crucial to understanding spatial variation in antipredator allocation and mortality. Key words: delayed dispersal, family group, goshawk Accipiter gentilis, population dynamics, predation, risk taking, sparrow hawk Accipiter nisus. [Behav Ecol]

Survival benefits and divergence of predator-induced behavior between pumpkinseed sunfish ecomorphs

Resource use is widely thought to influence adaptive phenotypic divergence, whereas other ecological factors, such as predation, are frequently overlooked, particularly in studies of polyphenism in fishes. Juvenile pumpkinseed sunfish (Lepomis gibbosus) reared with predatory walleye (Sander vitreus) increase body depth and dorsal spine length, indicating that developmental responses to predation can shape phenotype. Body form responses to the same predator cues though have also evolutionarily diverged between sunfish ecomorphs that coexist in single lake populations by inhabiting either littoral or pelagic habitats, suggesting that predation risk varies between habitats. Here, we test if prior exposure to predator cues influences the development of behavior in juvenile pumpkinseed sunfish, if behavioral responses to the same predator cues vary between ecomorphs, and if induced phenotypic variation affects survival under predation. Behavior depended strongly on prior exposure to predator cues, but this effect varied between sunfish ecomorphs, indicating that ecomorphs have different responses to the same predator cues. Predator-induced phenotypes had higher survival than control phenotypes under simulated littoral but not pelagic conditions. Predator-induced phenotypic responses are candidate-inducible defenses, and divergent responses between ecomorphs suggest that they can evolve in response to selection imposed by differences in habitat-specific predation risk. Key words: evolution, induced defense, Lepomis gibbosus, phenotypic plasticity, polymorphism, predation. [Behav Ecol]

Metrics for Studies of Resource Selection

Resource availability and resource use are 2 key concepts in studies of resource selection. Although equal accessibility to resources is one component defining resource availability, we rarely know what restricts access to resources. Consequently for spatially distributed resources, the animal's use of space in association with the occurrence of resources is a frequent basis for inferring resource use and testing for resource selection. For many resources, occurrence can be defined for the population or the individual animal and requires that researchers specify the spatial extent of resources an animal might use during the time interval of study (e.g., the “choice set”). Often the occurrence of resources is defined at multiple scales, which facilitates understanding hierarchical selection patterns. We discuss numerous factors and criteria that should be considered when delineating the area an animal might use during a period of interest. New analytical approaches to resource selection, including resource utilization functions (RUF) and discrete choice modeling, help address some of the issues of defining availability and dealing with the behaviors associated with resource use. A currency of use is a measure of the investment made by an animal in securing resources, avoiding loss of resources, or otherwise optimizing fitness. Common currencies used by researchers include time spent or distance traveled in a cover type, use of event sites (e.g., nest sites, roosting sites, den sites), or amounts of different kinds of foods consumed. Less common, but potentially highly informative, are such currencies as energy expended or predation risk or other risk incurred. Simulation of animal movements interspersed with diel resting periods, through habitat types with activity-dependent energy expenditure and habitat-specific predation risk showed that choice of a currency of use strongly influences inferences about habitat selection. We argue that perhaps the most informative currency of use would be increased risk to fitness accepted by an animal. Although fairly simple conceptually, such application of risk assessment faces formidable empirical challenges and is a worthy goal for the next generation of researchers of animal resource selection.

Habitat overlap of enemies: temporal patterns and the role of spatial complexity.

Environmental heterogeneity can promote coexistence of conflicting species by providing spatial or temporal refuges from strong interactions (e.g., intraguild predation, competition). However, in many systems, refuge availability and effectiveness may change through time and space because of variability in habitat use by either species. Here I consider how the intensity of intraguild predation risk varies from day to night for aquatic insects that use both vegetated and open water habitats. Large (1,265 l) and small (42 l) mesocosms were used to test the hypothesis that Buenoa would choose an open-water habitat that minimized predation by the ambush predator Notonecta during the day, but that at night Buenoa would safely use both vegetated and open water. Regardless of container size, Notonecta remained in vegetated water during the day and exploited both habitats at night, despite exhibiting greatest instantaneous predation rates in open water during the day. In contrast, Buenoa maintained an even distribution throughout the mesocosms during day and night, even though habitat-specific predation risks were fivefold lower in open waters than in vegetation during the day and habitat-specific predation risk would have been reduced threefold by fully exploiting open waters. Thus, temporal heterogeneity was both beneficial and detrimental to Buenoa; darkness of night reduced predation, but spatial refuges also disappeared. Together, these patterns suggest that while environmental heterogeneity can dampen intense biotic interactions, enemies do not select habitats solely on the basis of conflict avoidance. Instead, it appears that habitat-specific variation in other biotic (e.g., visual predators) or physical factors (e.g., UV radiation) may also mediate species interactions by influencing habitat selection.

Mechanisms Underlying Habitat Use of Juvenile Largemouth Bass and Smallmouth Bass

Differences in habitat use between adult largemouth bass Micropterus salmoides and adult smallmouth bass M. dolomieu have been well documented, with largemouth bass occupying vegetated habitats and smallmouth bass occupying areas with cobble substrate. However, less is known about the habitat use of juveniles. Direct observations of three co-occurring populations of largemouth bass and smallmouth bass in New York State indicated that habitat use by age-0 fish was very similar to that of adults. To examine potential mechanisms underlying this pattern of habitat use, we conducted a pair of laboratory experiments. The first experiment, concerned with habitat-specific feeding rates, found that juvenile largemouth bass consumed aquatic insects at equal rates in vegetated and cobble habitats. In contrast, smallmouth bass fed at higher rates in cobble than in vegetation. The second experiment, which examined habitat-specific predation risk, found qualitative differences between the two species. Largemouth bass were more vulnerable to predation in cobble than in vegetation, whereas the predation vulnerability of smallmouth bass was higher in vegetation than in cobble. Together, the two laboratory experiments suggest differences between juvenile largemouth bass and smallmouth bass that may underlie the observed specialization for different habitats.

Effects of Littoral Habitat and Fish Predation on the Distribution of an Exotic Crayfish, Orconectes rusticus

In northern Wisconsin lakes, patterns of spatial distribution of an exotic crayfish, Orconectes rusticus (Girard), were related to differences in four littoral zone habitats: cobble, sand, macrophyte/firm (vegetated firm sediments), and macrophyte/much (vegetated soft sediments) in northern Wisconsin lakes. Field surveys of crayfish abundance and mortality rates of tethered crayfish were used to determine the relationship of habitat-specific predation risk to cross-habitat patterns of crayfish distribution. Predation risk differed significantly across habitat types; crayfish on sand (particularly small crayfish, 15-18 mm carapace length) experienced significantly higher predation than crayfish in either cobble or macrophyte habitats, which were not significantly different. Crayfish use of cobble and sand habitats was inversely related to habitat-specific predation risk, whereas use of macrophyte/firm and macrophyte/muck habitats was not related to predation risk. Crayfish use of these latter habitats may be related to physical attributes of substrate (e.g., physical impediment to crayfish movement). An additional survey of crayfish habitat use and fish predator density in seven lakes was consistent with these results. Crayfish were overrepresented in cobble relative to its availability, used sand in proportion to its availability, and were underrepresented in macrophytes. Among the seven lakes, crayfish use of cobble was significantly and positively correlated with lakewide predator density, suggesting the potential importance of predation risk in structuring patterns of crayfish distribution. The combination of the crayfish's association with cobble habitat and the low predation risk associated with cobble suggests that cobble availability may significantly influence the success of O. rusticus invasions.