Habitat Selection

1. Habitat Selection • Animals that move freely across habitats and exercise selectivity in their location can influence community patterns through habitat selection

2. Habitat Selection • Habitat selection provides one possible explanation for the conspicuous absence of highly mobile, readily dispersing species from an apparently suitable community • As with most community patterns, chance evens or exclusions caused by direct interactions with other species produce similar patterns

3. Habitat Selection • Habitat selection can function like a selective filter between a developing community and the species pool of potential members by sorting among species that can actively avoid or choose to colonize a particular place

4. Habitat Selection • Those choices often depend on the kinds of interactions that are likely to occur with other species that are already present in the community • Factors that influence habitat selection include the avoidance of physiological stress, the availability of prey or the necessary resources, and the avoidance of competitors and enemies

5. Habitat Selection • Animals respond to combinations of these factors in complex ways, and there is some evidence that some animals make relatively sophisticated choices by weighing foraging advantages against mortality risks in particular sites

6. Habitat Selection • Although much of the research to date has focused on higher vertebrates (birds), field observations and experiments show that even animals with modest sensory abilities appear to show strong preferences for favorable habitats

7. Habitat Selection • Evidence for habitat selection comes from studies using a variety of approaches • One approach draws on natural history observations to associate the presence of particular species with biotic or abiotic features of the habitat

8. Habitat Selection • Correlative studies linking the presence/absence of organisms to habitat features can be determined through statistical analysis (e.g. logistic regression) or the abundance can be modeled against multiple habitat features (multivariate analysis)

9. Habitat Selection • These are correlative as they assume the association displayed by highly mobile organisms is an active decision • Others have used direct experimental manipulation of the factors thought to influence habitat choice

10. Habitat Selection: Correlations • The observation that some mobile organisms are found in certain habitats and not in others is de facto evidence for habitat selection • Early work by MacArthur (1958) on microhabitat use by coexisting warblers is one of the examples of this approach

11. Habitat Selection: Correlations

12. Habitat Selection: Correlations • There are patterns of correlation between habitat complexity and species diversity

13. Habitat Selection: Correlations • There have been more detailed studies showing the correlation between actual species composition of forest vegetation and of birds (with respect to particular foraging guilds and vegetation)

14. Habitat Selection • Different groups of birds species responded to aspects of variation in plant species composition in northern hardwood forest

15. Habitat Selection • Wiens and Rotenberry (1981) examined avian community structure in a simpler shrub-steppe habitat and found the community relatively species poor and relatively weak habitat associations

16. Habitat Selection: Cues and Consequences • Sebens (1981) documented an interesting example of habitat selection by settling larvae of the large Pacific sea anemone (Anthopleuraxanthogrammica) • The adults are sessile sit-and-wait predators, typically eating bi-valve mollusks • JunvenileAnthopleuratend to occur selectively in dense patches of the bivalve molluskMytilus

17. Habitat Selection: Cues and Consequences • Habitat selection based upon prey availability

18. Habitat Selection: Cues and Consequences • Grosberg (9181) has experimentally shown that several species of settling invertebrates will discriminate among substrates based upon density of potential competitors that may encounter

19. Habitat Selection: Cues and Consequences • The dominant competitor in the fouling community (MA) is a small tunicate (Botryllus) • It tends to overgrow and displace many of the other sessile species • Grosberg coaxed different densities of Botryllus larvae to settle on small glass plates

20. Habitat Selection: Cues and Consequences • He then looked at how potential competitors settled after the different Botryllusdensities were established • One group actively discriminated against plates with high densities (suggesting strong ability to detect competitors) the others did not (although consisted mostly of species able to elevate feeding structure above Botryllus)

21. Avoidance (A) or tolerance (B) of the competitor Botryllus

22. Habitat Selection: Cues and Consequences • A number of species, both vertebrates and invertebrates, appear to select against habitats that contain predators • Sih (1982) looked at habitat use by different size classes of the predatory aquatic bug Notonecta(which are cannibals)

23. Habitat Selection: Cues and Consequences • Use of different portions of the stream pools by large and small Notonecta appears to reflect compromises between selecting habitats with abundant food and avoiding cannibalistic predation by adults • Instars 1-3 avoid adults and forage at the edge while adults forage at the center of pools (and upon removal, smaller instars moved to the center)

24. Habitat Selection • Site dependent patterns of habitat use by different instars of Notonecta in pools with and without cannibalistic adults

25. Habitat Selection • Other kinds of organisms appear to make similar ontogenetic shifts in habitat use that depend on the presence of predators. • Although the costs of predator avoidance seem slight, Morin (1986) observed that tadpoles of the spring peeper spent the first 2 weeks after hatching hidden in the bottom litter layer of artificial ponds

26. Habitat Selection • As they grew, they moved off the bottom to forage in more conspicuous locations (but only in ponds without predators) • In ponds containing predators (newts), they remained hidden at the bottom during the entire 2 month larval period

27. Habitat Selection • Holomuzki (1986) studied patterns of microhabitat use by larvae of the tiger salamander, Ambystomatigrinum, in ephermeral ponds in AZ.

28. Habitat Selection • Ambystoma changed their diel patterns of microhabitat use in ponds with an important predator Dytiscus • Dytiscus tend to forage primarily at night in shallow water; at which time Ambystoma move into deeper water

29. Habitat Selection

30. Habitat Selection: Conflicting Demands • Some studies have shown that adults of some species can detect the presence of potential competitors and predators of their offspring and can select sites for their offspring to minimize some of those risks

31. Habitat Selection: Conflicting Demands • Experimental manipulation of the abundance of potential predators and competitors that interact with larvae of the southern gray tree frog Hylachrysoscelis

32. Habitat Selection: Conflicting Demands • Using artificial small ponds, they counted the number of calling males at ponds containing different risks (species) • 1) no predators or competitors • 2) intraspecific comp • 3) intersp. Comp • 4) adult salamander • 5) larval salamander • 6) fish • 7) dragonfly larvae

33. Habitat Selection: Conflicting Demands • Males avoided ponds with conspecific larvae or fish • Females avoided any predator • Both male and female appear to select against comp/predation

34. Habitat Selection: Conflicting Demands • Other studies have explored the trade-offs between opportunities for foraging and predation risk • Consider blue-gill sunfish; small fish forage most efficiently in open water on zooplankton but are also vulnerable to largemouth large-mouth bass in those same habitats

35. Habitat Selection: Conflicting Demands • Consequently, small bluegills preferentially use nearshore vegetated habitats, because these habitats greatly reduce the risk of predation by bass

36. Habitat Selection: Conflicting Demands • Effects of +/- of predator (largemouth bass) on habitat use and growth rates

37. Habitat Selection

38. Habitat Selection