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Chapter 3: Climatic determinants of global patterns of biodiversity

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Edited by Peter Moyle & Douglas Kelt
By Douglas A. Kelt, September 2004

Consequences of global climate patterns
We have learned much about the global distribution of climate in this chapter. What can this tell us about the distribution of plant and animal life? Because climate strongly influences soil production we might expect to find very different soils under different climatic regimes. This is the case and it obviously influences the distribution of plants. Additionally, plant growth often is limited by water availability, so the plant abundance might be expected to relate to climate – and it does; tropical trees and vines are highly unlikely to survive in a desert environment. On the other hand, many plant species that do quite well in deserts have very poor defenses against fungal pathogens, and these fare poorly in moist climates. Additionally, understanding climate gives an indication of where you would find animals that are particularly good at surviving on little water or animals that require high humidity and/or frequent rains. If you are studying animals that live at high latitudes, understanding the climatic regime there greatly improves your understanding of their natural history. If you work with marine systems this will give you some important insights into the transport of the eggs of your focal species (consider the global circulation of water), or of their food items (think of upwelling). At smaller scales we often see differences in plant and animal communities across very short distances. The three local influences discussed above have strong influences on where animals move in their daily travels. Think of the redwood trees that make California's coast so renowned. Think of the salmon populations that are well fed off our coasts. Look at a map of California and consider the distribution of deserts, grasslands, oak woodlands, conifer forest, alpine and tundra, and consider the daily and seasonal changes in temperature and precipitation that organisms face in these different habitats.

However, on a simpler level it is useful to recall that through process of evolution animals become adapted to the environment in which they live. The large variations in local climate that we have discussed here – from large scale differences such as the difference between tropical and boreal habitats to small scale differences such as the foggy redwood forests of northern California versus the warm and dry Sierra foothills to the hot and very dry Mojave and Colorado Deserts – provide a seemingly endless array of environments to which species may adapt. Thus, we see different lizard species in Palm Beach than we do in Eureka, and different plants as well. We even see different plant communities in the coastal and Sierra mountains of the state, and on different faces of a single hillside. Understanding local and regional climate and the factors governing these can provide important insights into the influences that have led to such tremendous diversity in California as well as elsewhere.

Finally, the general similarities in climate at very distant parts of the globe often lead to superficially similar habitats, and it is not uncommon to find similar adaptations to these environments by unrelated taxa. When animals find evolve similar means of coping with their environments in different parts of the world we say that they have converged on a similar strategy. Some examples of ecological convergence in mammals include (Fig. 10) capybaras (the world's largest rodent; South America) and hippopotamus (Africa), kangaroo rats (North America) and jerboas (Asia and Africa), wolves (North America and Eurasia) and the Tasmanian wolf (really a marsupial; Australia), and flying squirrels (North America) and flying phalangers (another marsupial; Australia). Numerous examples also exist for birds, reptiles, fishes, plants, and other groups.

Fig. 10. Drawings of pairs of species of North American (placental) and Australian (marsupial) mammals purporting to show convergence. Note that figures such as this may be misleading, as the animals represented are not all drawn to the same scale, and the convergence demonstrated in general physical structures may not be reflected in many other features. For example, North American kangaroo rats look very similar to Asian jerboas, but the former eat almost entirely seeds and can live without free water, whereas the latter are largely folivorous (eat leaves) and require free water in their food or through drinking. Thus, physical convergence does not necessarily imply functional convergence (from Brown and Lomolino 1998 “Biogeography” Sinauer).

Table of Contents

1. Roots of the modern environmental dilemma: A brief history of the relationship between humans and wildlife
2. A history of wildlife in North America
3. Climatic determinants of global patterns of biodiversity
4. Biodiversity
5. Natural selection
6. Principles of ecology
7. Niche and habitat
8. Conservation biology
9. Conservation in the USA: legislative milestones
10. Alien invaders
11. Wildlife and Pollution
12. What you can do to save wildlife

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