Rethinking Adaptation

WHAT IS NICHE CONSTRUCTION?

Termite Mound

Termite mound

Organisms, through their metabolisms, activities and choices, define and partly create their own niches. They may also partly destroy them. This process of organism-driven environmental modification is called niche construction. Niche construction regularly modifies both biotic and abiotic sources of natural selection and, in doing so, generates forms of feedback that change the dynamics of the evolutionary process.

 

Although niche construction is a widely recognized phenomenon (it is obvious that it happens) at present its consequences are neither well described nor well understood. For example, adaptation as currently conceived is a process by which natural selection effectively moulds organisms to fit pre-established environmental templates. Environments pose ‘problems’ and those organisms best equipped to deal
with the problems leave the most offspring. Despite the recognition that processes independent of organisms change the worlds to which populations adapt, the changes that organisms bring about in their own worlds are seldom considered in evolutionary
analyses.

Cuckoo

Cuckoo chick being fed by host

To varying degrees, however, organisms choose their own habitats, mates and resources, construct important components of their local environments, such as nests, holes, burrows, paths, webs, dams and chemical environments, and choose, protect andprovision ‘nursery’ environments for their offspring. Hence, organisms not only adapt to their environments but in part they also construct them. Many natural selection pressures to which organisms are exposed exist, in part, only because of the prior niche-constructing activities
of organisms (1).

A SECOND ROUTE TO ADAPTATION

The role of niche construction is depicted in the table below. Each organism at any point of time is described by a set of features, or traits, such as an arboreal lifestyle, or a frugivorous diet, here represented by an array of lower case letters (c, n, h, k, q, j). Similarly, the organism’s environment could hypothetically be decomposed into an array of factors, for instance, the local temperature or the
presence of a predator, here represented by upper case letters (A, B, N, H, K, Q, Z, L). The description of an organism as adapted to its environment corresponds to a complementary matching of the organism’s features and its environment’s factors, represented here by a matching of letters.

The match between organism and environment

Thus at time t, the organism is well adapted to its environment according to the high level of feature-factor matching (n-N, h-H, k-K, q-Q) but there are also some mismatches (c-B, j-Z). At time t+1, as a consequence of the action of natural selection, the match has been enhanced through the selection for individuals with feature z at the expense of those with feature j. At time t+2 the match has been enhanced in a different manner, through positive and counteractive niche construction.

Here the organism modifies environmental factor B to become C, generating the c-C match. For instance, the population of organisms offsets a scarcity of food in their environment (B) by relocating to a new environment (C). At time t+3 through negative and inceptive niche construction, however, the organism modifies environmental factor N to D generating a new mismatch (n-D). For instance, the excrement of a population of burrowing mammal pollutes their burrows to the point where they become uninhabitable. At time t+4 this leads to natural selection that favours individuals with feature d at the expense of those with feature n.

For instance, in our mammal example, natural selection now favours individuals that deposit their faeces at a latrine site away from the burrow. The table illustrates the fact that the complementary match between organism and environment can be brought about by two processes, and not just one, that is, by niche construction as well as through natural selection.

AN EXAMPLE OF NICHE CONSTRUCTION

Turner (2) describes how earthworms have the anatomy and physiology of freshwater animals, yet live in soil. They are able to survive because they modify the soil to suit their physiology, through activities such as choosing the optimal soil horizon, tunnelling, exuding mucus, eliminating calcite, and dragging leaf litter below ground. This is an example of the positive niche construction portrayed in step t+2 of the table above.

Earthworms

How earthworms modify their environment

1. Lewontin 1983 2. Turner 2000