ECOLOGY

1. Introduction.
A population is a collection of individuals of the same species that live together in a
region. Population ecology is the study of populations (especially population abundance)
and how they change over time. Crucial to this study are the various interactions between
a population and its resources. A population can decline because it lacks resources or it
can decline because it is prey to another species that is increasing in numbers.
Populations are limited by their resources in their capacity to grow; the maximum
population abundance (for a given species) an environment can sustain is called the
carrying capacity. As a population approaches its carrying capacity, overcrowding means
that there are less resources for the individuals in the population and this results in a
reduction in the birth rate. A population with these features is said to be density
dependent. Of course most populations are density dependent to some extent, but some
grow (almost) exponentially and these are, in effect, density independent. Ecological
models that focus on a single species and the relevant carrying capacity are single species
models. Alternatively, multi-species or community models focus on the interactions of
specific species.
The discipline of population ecology holds a great deal of philosophical interest.
For a start, we find all the usual problems in philosophy of science, often with new and
interesting twists, as well as other problems that seem peculiar to ecology. Some of the
former, familiar problems from philosophy of science include the nature of explanation
and its relationship to laws, and whether higher-level sciences (like ecology) are
reducible to lower-level sciences (like biochemistry). Some of the philosophical problems
that arise from within population ecology include whether there is a balance of nature and
how the uneasy relationship between the mathematical and empirical sides of the
discipline might be understood. As we shall see, many of these questions are intricately
linked, and providing satisfactory answers is no easy matter. But there is no doubt that
there are important lessons for philosophy of science to be gleaned from the study of
population ecology.
In what follows I will focus on some of the central questions that are prominent in
the recent philosophy of population ecology literature. There are, of course, other
questions and problems, some of which the interested reader may pursue in the works
listed in the references and further reading. But despite this admittedly less than
comprehensive treatment of the philosophical issues in population ecology, those I
address will give a sense of the flavor of the philosophical issues that arise in population
ecology.
It is worth mentioning that many of the philosophical problems in population
ecology are of great importance to working ecologists. For example, the issue of whether
there are laws in ecology is seen by many ecologists as an important internal question to
their discipline and one that has immediate methodological implications. (If there are no
laws, ecologists might settle for a more pragmatic and even pluralist attitude towards
their models.) Philosophers have been a little slow to turn their attention to ecology and
so working ecologists have had to tackle many of the philosophical issues themselves. As
a result a great deal of the philosophical ground work has been carried out (for the most
part, with a high degree of philosophical sophistication) by working ecologists. (See, for
example, Ginzburg, 1986; Pimm, 1991; and Turchin, 2001) But the philosophical
problems in population ecology are important in another way. Population ecology itself
has a great deal of social and political significance. Conservation management strategies
often depend on predictions of population ecology. Where population ecology meets
conservation management we find that philosophy of science meets ethics. Typically a
great deal more than scientific or philosophical curiosity hangs on the answers to the
philosophical and scientific problems faced by population ecology. For example,
scientific issues about burden of proof in hypothesis testing have a distinctly ethical
dimension. I will say more about such matters in section 6.