Habitat Use, Selection and Preference

Transcription

1 , Selection and Preference ESRM 450 Wildlife Ecology and Conservation Habitat any area offering the resources and conditions that promote occupancy by a species any area offering the resources and conditions that promote occupancy by a species Definition transcends floristic composition; resources include food, cover, shelter, other factors influencing occupancy species-specific scale-dependent e.g., a forest may be habitat for a flying squirrel, but at a finer spatial scale certain trees may not has temporal component (e.g., resources can wax and wane) 1

2 1/2/15 any area offering the resources and conditions that promote occupancy by a species Definition transcends floristic composition; resources include food, cover, shelter, other factors influencing occupancy species-specific scale-dependent e.g., a forest may be habitat for a flying squirrel, but at a finer spatial scale certain trees may not has temporal component (e.g., resources can wax and wane) Means that habitat is not always wilderness Human activity can both create and destroy habitat (e.g., cottontail rabbits and jackrabbits) Cottontails and Jackrabbits Conversion of open rangeland to farmland has created habitat for eastern cottontail rabbits (Sylvilagus floridanus) utilize hedgerows, gardens seek cover along fences But has constricted white-tailed jackrabbit (Lepus townsendii) habitat depend on the open prairie any area offering the resources and conditions that promote occupancy by a species Definition provides basis for explaining why animals are in some areas, not others - An area provides the necessary resources and conditions for a species or does not 2

3 Habitat Quality Habitats vary in quality Quality: degree to which habitat promotes individual fitness, and by extension population growth continuous variable linked to demography, not density or vegetative characteristics Why not density? Habitat Quality Habitats vary in quality Quality: degree to which habitat promotes individual fitness, and by extension population growth continuous variable linked to demography, not density or vegetative characteristics Why not density? Animals can congregate in, or be forced into, areas where they fare poorly Habitat Quality Habitats vary in quality Quality: degree to which habitat promotes individual fitness, and by extension population growth continuous variable linked to demography, not density or vegetative characteristics Why not density? Animals can congregate in, or be forced into, areas where they fare poorly Why not vegetative characteristics? 3

4 Habitat Quality Habitats vary in quality Quality: degree to which habitat promotes individual fitness, and by extension population growth continuous variable linked to demography, not density or vegetative characteristics Why not density? Animals can congregate in, or be forced into, areas where they fare poorly Why not vegetative characteristics? Remember, a particular plant association may promote high fitness in one animal species but not another The way an animal uses the collection of conditions and resources in a habitat Typically measured as relative amount of time spent in different areas within habitat More time in certain area means more use of resources or conditions at that location Can be measured for individuals, populations Patterns of habitat use can vary with behavior foraging, denning, hiding, resting behavior-specific habitat use patterns often specified (e.g., foraging habitat use ) 4

5 1/2/15 Habitat use is also Scale-dependent a forest might be used at a large scale, but certain parts of a forest won t be used at a finer scale (when we zoom in) Subject to temporal variability e.g., patterns of habitat use can change seasonally Foraging Dugong Dugong (Dugong dugon) Deep channels (> 6 m in depth) Shallow water (< 4.5 m in depth) Pattern is temporally variable Wirsing et al. (2007) Oecologia Are habitat use patterns necessarily a reflection of choice? 5

6 1/2/15 No, because they are realized e.g., observed patterns of habitat use may be driven entirely by Predation (spatial and temporal patterns of mortality) Competition (exclusion; e.g., blue mussels Mytilus edulis) These forces are external constraints But, habitat use patterns can reveal resources and conditions that are important drivers of fitness, and by extension distributions and population dynamics Studying Explaining habitat use is a cornerstone of wildlife ecology but how do we identify the resources and conditions that affect habitat use? 6

7 1/2/15 Studying Explaining habitat use is a cornerstone of wildlife ecology but how do we identify the resources and conditions that affect habitat use? Two approaches (1) Experimental (manipulative): alter factors that may be influential (perturbation may be temporal and/or spatial; lab or field-based) (2) Observational (mensurative): relate use to natural variation in factors that may be influential (temporal and/or spatial) Why are most habitat use studies observational? Use-Only Approaches Resource Utilization Functions (RUF): observational approach to understanding animal habitat use, typically within the home range Step 1: obtain raw locations - e.g., via observation, telemetry Kertson and Marzluff (2010) Environmental Conservation Step 2: Convert Raw Points to Utilization Distribution (UD) UD: Probability density function (pdf) quantifying time allocation, or concentration of use, within home range Sums to 1 3D, use = height (volume) of UD 7

8 Animal relocations Utilization Distribution Sampling grid Ruf.fit (multiple regression) Use and habitat covariates The Final Step: A RUF RUFs: multiple regression equations that relate intensity of use to resources in a specified area, typically within an animal s home range - coefficient estimates not overlapping zero indicate influential resources Habitat Selection The process, both innate and learned, by which animals choose which habitat components (conditions, resources) to use 8

9 Habitat Selection To really know what an animal is choosing, we would have to understand its decision-making process - all but impossible in most cases So, we use indicators of choice to infer selection of particular conditions and resources One popular indicator: use relative to availability - Overuse = selection; underuse = avoidance - Some techniques: randomization, resource selection functions (RSFs) - Challenge: determining what is available Habitat Selection by Tiger Sharks 0.1 Use (observed expected) Selected No Pattern Shallow Banks Deeper Waters Avoided *Availability determined using randomization of shark tracks Heithaus et al. (2002) Marine Biology Selected: used to degree exceeding availability Avoided: used less than expected from availability Resources Telemetry (red), Random (yellow) points Warton and Aarts (2013) J Anim Ecol 9

10 avoided Amur leopard (Panthera pardus orientalis) Selected (big surprise!) Hebblewhite et al. (2011) Biological Conservation Predicting Potential Habitat Associated with avoided resources Associated with selected resources Hebblewhite et al. (2011) Biological Conservation Habitat Preference Selection of one habitat component over another when both are equally available Hard to demonstrate without cafeteria-style experiments So we stick with use and selection to be safe 10

11 /Selection and Conservation Understanding of habitat use/selection facilitates effective management, conservation Identify habitats used intensely by the species of interest and those that seem to be avoided (selection) Manage for habitats used/selected for specific activities (e.g., foraging, reproduction, denning) Most importantly, if we understand mechanisms underlying use/ selection, we can predict how anthropogenic changes to landscape are likely to affect animal distributions, populations A Caveat Management based on habitat use/selection snapshots can be problematic Observed pattern could be anomalous Doesn t allow us to say much about how animal distributions might change following landscape alteration (e.g., as a result of human disturbance) Five Minute Paper Questions & Insights 11