In the last chapter we saw that human activity is leading to significant levels of destruction of natural habitats. We can and did put some figures on the levels of destruction. In this chapter we consider the effects that these levels of destruction might have on populations, species and communities.

By reading this chapter students will gain an understanding of the effects of habitat destruction and fragmentation on communities of species, on populations, and on genetic diversity within populations. They will gain understanding of how fragmentation of habitat decreases the species diversity and increases the probability of species extinction at the site and landscape scales.

Introduction

There is an intimate and complex relationship between a species and its habitat and the former has certain requirements for persistence: either abiotic (e.g. microclimate) or biotic (e.g. food or symbionts) that their habitat provides. In some species, habitat requirements are much more specific than others (some are specialists and some generalists), but there are usually definable elements that are vital, even for generalists, especially for successful reproduction. If a species has been sufficiently well studied, its presence or absence can often be predicted on the basis of presence or absence of key habitat features, and it follows that if these key features are removed the species will disappear also.

Deterministic versus stochastic effects of habitat loss

The scale of destruction described in the previous chapter means that the habitats of some species have been lost completely.