Lecture 5: Habitat Selection Definitions Habitat = place where an animal lives Habitat selection = process by which an animal chooses a place to live (over another) Limiting factor = resource or environmental condition that limits an animal?s abundance and distribution Generalists and specialists Habitat generalists ? wide range of habitats and tolerate various conditions Able to live in many different areas, but not ideally suited to any specific habitat Not the most competitive in any one habitat Habitat specialists ? narrow range of habitats Strong competitors in their preferred habitat, but vulnerable to habitat loss Disproportionate amount of habitat specialists being affected because of habitat loss Ultimate and proximate factors How and why particular types of behavior (like habitat selection) evolve? Ultimate factors = determine how well animal will survive and reproduce in is chosen habitat Proximate factors = provide animal with cue that the right conditions are in a certain location Don?t necessarily effect how it reproduces Ex: Habitat selection of breeding birds Ultimate factor: food availability when chicks are in the nest Food availability in many cases, particularly when they have the highest energy demands Proximate factor: general appearance of the vegetation in early spring Because that?s when they?re setting up their territory and returning from migration Limiting factors Food availability Often the most important limiting factor Most species reach their highest population densities when food is most abundant Water Important in dry or seasonally dry climates Animals that require free liquid water can only live in areas near a water source Birds can roam farther than zebras Amphibians require water for breeding and to keep their skin moist Cover Provides protection from weather or predators Especially important in winter when animals are thermally stressed Cold environment (for at least part of the year) Temperature Animals prefer habitats where it is easiest for them to maintain their heat balance Spend more time in thermal neutral zone so require less energy Habitat preferences may vary seasonally Example: prefer warmer south-facing slopes in winter and cooler north-facing slopes in summer Soil Soil texture is important for fossorial (burrowing) animals Soil type determines whether minerals and other nutrients will be present in plants in sufficient quantities for herbivores Which minerals are present Reproductive sites Important for animals with special requirements for nests or dens Examples: presence of large dead trees for cavity nesting birds Primary cavity nesters ? make their own cavities Secondary cavity nesters ? use abandon cavities made by other animals Predators Especially important during reproductive season when youg and attending parents are most vulnerable Example: ground-nesting seabirds may be restricted (or nest most successfully) to islands where predators are absent Problem now is that some islands have predators introduced by humans Social structure/social organization In territorial species, animals can only occupy habitats where there are undefended territories In solitary species, animals may be restricted to habitats where they can find a mate Social vs. territorial Inheritance and learning Inheritance: genetically encoded preferences for certain habitats Can be shaped by learning Learning: modification of inherited preferences based on experience Mechanisms involved in learning Habitat imprinting = habitat preference acquired through exposure early in life Critical period early in animals developmental period, (reason for (3)) Site tenacity = tendency for animals to return to the same location they occupied previously (or never leave) Can lead to conflicts with human development Philopatry = tendency for animals to return to or remain in the areas where they were reared Love of homeland Refers more specifically to area where animal was born Knowing when certain habitat will be suitable involves inheritance and learning Ex: habitat selection experiments on deer mice Two subspecies9races) : praire deer mouse and woodland deer mouse Experiment: released both wild-caught lab-reared mice of both races and observed habitat in which they settled Results: (*) ? No prior exposure, but go to habitat of their ancestry So indicated important role of learning, can have bigger role than inheritance Conclusion: inherit habitat preference (1), but can learn a new one (3), and will be lost over time if not reinforced (4). Released Observed (1) Wild-caught mice All select right habitat (2) Lab-reared, 1 generation 10-20% select wrong habitat(*) (3) Cross-fostered (reared by parents in other habitat) Most select habitat of foster parent (4) Lab-reared, 20 generations Random habitat selecting (no pattern)
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