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Biodiversity . Biodiversity . Are communities saturated? A closed system must balance the gains in energy from net production with those taken by consumers and decomposers
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Biodiversity • 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)
Biodiversity • However, remember most systems are not truly closed
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?
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)
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
Biodiversity • 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
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
Biodiversity • Who is abundant changes as we go across space (Husak and Linder 2004) • E.g. Woodthrush
Biodiversity • Communities may have similar numbers of individuals or biomass (why?), but vary on the species richness (why?)
Biodiversity • In some communities, individuals may be ‘packed’
Latitudinal Gradients in Diversity • A prevalent global pattern of species diversity has intrigued evolutionary ecologists for some time
Latitudinal Gradients in Diversity • So what are the proposed mechanisms generating said pattern? (Table 18.1)
Latitudinal Gradients in Diversity • 1) Evolutionary time • Assumption is that diversity increases with time • Temperate habitats relatively impoverished due to short existence
Latitudinal Gradients in Diversity • 2) Ecological Time • Similar to (1), but constraints are more related to dispersal and lack of saturation
Latitudinal Gradients in Diversity • 3) Climate Stability • A stable climate allows for greater specialization
Latitudinal Gradients in Diversity • 4) Climate Predictability • Again allows for specialization (e.g. annual succession of primary production or desert plants and biannual rains)
Latitudinal Gradients in Diversity • 5) Spatial Heterogeneity • Forests almost always contain more animals than does a grassland
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)
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
Biodiversity • 8) Competition • When competition is strong, selection favors production of a few strong competitors • Furthermore, strong competition also favors reduction in niche breadth
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
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
Biodiversity • Clearly, many of these forces can act in concert
