Biology 6C- Spring/Summer 2008
Designing an Ecological Study
General Ecology Laboratory Manual
What kinds of questions do ecologists study?
How can one identify an ecological topic for investigation?
What steps do ecologists follow in testing hypotheses about ecological systems?
Ecology can be defined as the study of ecological systems. A
is any set of components, living or
nonliving, that are tied together by regular interactions. An
is made up of one or more organ-
isms, together with the nonliving environment with which they interact. Ecological systems exist at several
different levels of organization. An ecological system can be a single organism and its surroundings, a
population or set of interacting populations in a certain habitat, or the entire community together with the abiotic
environment with which these species interact, a unit termed an
Ecologists are interested both in the structure and function of ecological systems.
measurable conditions of the system at one point in time. These include biotic attributes such as the body
mass of an organism, the density of individuals in a population, the ratio of predator numbers to those of a prey
species, or the biomass of all species that share some basic feature, such as photosynthesis. Structure also
includes the physical and chemical conditions that prevail in the space occupied by organisms.
refers to the processes that create structure at a given instant, and how these processes are affected
as structure changes. Function includes, for example, the relationships that determine the growth rates of
organisms, the rates of survival and reproduction of individuals in populations, the rates of predation by one
species on another, and the intensity of other interactions, such as competition and mutualism. These
processes determine the distribution and abundance of species, and thus the makeup of communities and
ecosystems. Function also includes system-level processes, such as the cycling of nutrients and flow of energy
among the components of an ecosystem.
A major goal of modern ecology is to understand how ecological systems function, so that their behavior can
be predicted, and so that they can be managed for long-term human benefit. To this end, ecologists seek to be
rigorous in their techniques of investigation.
What is the hypothesis-testing method?
Most ecologists use the hypothesis-testing or hypothetico-deductiveapproach in their studies. This
approach, based largely on the ideas of Karl Popper (1968), is the statement of explicit hypotheses about
ecological relationships, followed by collection of data that lead to their acceptance or rejection. It views
activities that cannot lead to rejection of certain hypotheses and the acceptance of others as wasted
efforts, which do not advance ecological knowledge. The need for a rigorous hypothesis-testing approach
has been stressed by many ecologists (Quinn and Dunham 1983, Connor and Simberloff 1986). The effort