Download
1 / 14
140 likes | 263 Vues
Chapter 22 delves into biodiversity, focusing on species richness, defined as the total number of species in an area. This measure indicates the heterogeneity of ecosystems, with greater diversity found in more complex habitats. Various factors contribute to biodiversity gradients, including historical context, climate, productivity, and competition. The chapter explains how species richness varies with location, particularly increasing towards the equator, and discusses the role of disturbances in enhancing diversity. It emphasizes the importance of taxonomists in classifying the estimated 5 to 30 million species on Earth.
E N D
Biodiversity • Species richness – the total number of species in an area • Simplest measure of biodiversity • Heterogeneity - higher when there are more species and they are equally abundant
Determining Species Richness • Species count depends on sample size • Relatively few species are very common • Estimated 5 – 30 million species exist on Earth: Only about 1.4 million are described • ~10% of all life • Taxonomists – people that describe and categorize species
Diversity Gradients • Diversity increases towards the equator
Factors That Might Cause Diversity Gradients • Eight Factors:
History Factor • Evolution = speciation • Tropics warmer and more humid, so they are more likely evolve and diversify faster • Tropical biotas are mature, temperate and polar are immature • All communities diversify over time
Spatial Heterogeneity • The more heterogeneous and complex the physical habitat, the more complex the animal and plant community the greater the diversity • Topographical relief important for species diversity • More habitats = more species • Highest diversity of US mammals occur in mountainous regions
Habitat Diversity Between Habitat (Beta) Diversity Within Habitat (Alpha) Diversity
Competition • In tropics: • animals and plants are more restricted in their habitat requirements increases between habitat (beta) diversity • Animals may also have a more restricted diet in each habitat, increasing within-habitat (alpha) diversity • Competition is keener in tropics, niches are smaller • Tropical species are more highly evolved and possess finer adaptations than do temperate species
Predation • Predators keep prey numbers so low, competition is reduced • Leads to an increase in types of prey, which leads to an increase in types of predators
Climate and Climatic Variability • More stable the climatic parameters and the more favorable the climate the more species • Similar to the history theory
Productivity • The greater the productivity the greater the diversity: everything else being equal • Data does not support this theory • Can be supported when put in the context of length of growing season (stability hypothesis)
Disturbance • If natural communities exist at equilibrium and the world is spatially uniform, then competitive exclusion rules and there will only be a few dominant species. • Moderate disturbance increases species diversity
