1. Biodiversity

2. Are communities saturated? A closed system must balance the gains in energy from net production with those taken by consumers and decomposers However, a predator (or anti-herbivory) strategy can keep a significant portion of the energy from entering the trophic food web (or routing most to decomposers)

3. Biodiversity However, remember most systems are not truly closed

4. Biodiversity Lots of questions emerge when we start thinking of what influences biodiversity How much does the degree of saturation vary within and between communities? Does efficiency vary across individuals and/or communities? What influences community saturation?

5. Biodiversity There is some evidence that at least some communities are indeed saturated Birds and foliage height evenly spaced out across three heights (fig 18.1)

6. Biodiversity While there are upper limits as to how many species can coexist in a particular point in time, there may be no upper limit across a larger area as species tend to replace one another

7. Biodiversity

9. One important way in which communities are different is the relative abundances of the species that comprise them Most are rare while a few are abundant Different mechanisms should produce different patterns

10. Biodiversity Who is abundant changes as we go across space (Husak and Linder 2004) More productive areas will have more ‘rare’ species to join community

11. Biodiversity Who is abundant changes as we go across space (Husak and Linder 2004) E.g. Woodthrush

12. Biodiversity Communities may have similar numbers of individuals or biomass (why?), but vary on the species richness (why?)

13. Biodiversity In some communities, individuals may be ‘packed’

14. Latitudinal Gradients in Diversity A prevalent global pattern of species diversity has intrigued evolutionary ecologists for some time

15. Latitudinal Gradients in Diversity

16. So what are the proposed mechanisms generating said pattern? (Table 18.1)

17. Latitudinal Gradients in Diversity 1) Evolutionary time Assumption is that diversity increases with time Temperate habitats relatively impoverished due to short existence

18. Latitudinal Gradients in Diversity 2) Ecological Time Similar to (1), but constraints are more related to dispersal and lack of saturation

19. Latitudinal Gradients in Diversity 3) Climate Stability A stable climate allows for greater specialization

20. Latitudinal Gradients in Diversity 4) Climate Predictability Again allows for specialization (e.g. annual succession of primary production or desert plants and biannual rains)

21. Latitudinal Gradients in Diversity 5) Spatial Heterogeneity Forests almost always contain more animals than does a grassland

22. Latitudinal Gradients in Diversity 6) Productivity More productive habitats allow for more individuals. Even if the diversity of prey (or energy) does not differ, it can lead to greater diversity. How? (fig. 18.5)

23. Latitudinal Gradients in Diversity 7) Stability of Primary Production Combining the ideas of productivity and stability Plants themselves will provide a more constant source of energy (e.g. seeds) if the energy they receive is more constant

24. Biodiversity 8) Competition When competition is strong, selection favors production of a few strong competitors Furthermore, strong competition also favors reduction in niche breadth

25. Biodiversity 9) Disturbance Disturbance can result in the continual density-independent removal of organisms from a community (thus allowing for new species to enter, even if competitively inferior) *Intermediate D-H

26. Biodiversity 10) Predation Similar to disturbance, predation may free up niches for other individuals to invade a community Furthermore, if a single species becomes too abundant, predators will ‘focus’ on that species

27. Biodiversity Clearly, many of these forces can act in concert

28. Thanks