Ecology, its Scope, its Methods,
its Goals
Reading: Smith and Smith, Chapter 1read, Chp 14, pps 257-263-read
carefully
Who am I?
Dr. Alan Molumby, 3092 SEL (behind 3084)
6-2994, or molumby@uic.edu (email is best)
What is Ecology?
• Ecology is the scientific study of the
distribution and abundance of organisms, and
their interactions with the environment
– The German Zoologist, Ernst Haekel defined
ecology as the “body of knowledge concerning the
economy of nature-the investigation of the total
relation of the animal to both its organic and its
inorganic environment; including above all, its
friendly and inimical relations with those plants
and animals with which it comes in contact......”.
– Humans have always had an interest in their
environment and their relationships to other
species
• in preindustrial times, this was critical to our
survival.
– A typical shaman from an indigenous tribe in
Southeast Asia, Africa, or the Neotropics, might
know several hundred plants; including their
uses, identification, and distribution.
– For instance: In the early 16th
century, European explorers
returned home from South
America with the dried bark of
the cinchona tree (Cinchona
officinalis) and reported its use
by natives of the New World as
a fever cure.
• This plant contained the alkaloid
quinine, to this day the most
effective treatment for malaria.
• Other examples include: cocaine,
curare, capsaicin, ipecac,
pilocarpine, coffee, and chocolate
cocaine
The Scientific Study of Ecology is Young
– The word ecology is derived from the Greek
oikos, which means “house”.
– European and American naturalists began to
call themselves “ecologists” in the late
nineteenth century.
• The first ecological societies and journals began to
appear in the early 20th century.
– Modern ecology relies upon the SCIENTIFIC
METHOD- ecologists employ both observational
methods and experiments.
Units of Ecology
• Ecologists work at the level of the individual
organism and higher.
– Some branches of ecology focus on this level;
physiological ecology and behavioral ecology are
concerned with how individual organisms are adapted to
the environment.
– The actions of individuals are the underlying basis of
population biology.
– In evolution, natural selection acts on individuals
– Individual organisms are easier to define in some taxa
(mice, rotifers, minnows) than others (aspen, colonial
protozoa, gorgonians).
• Species is an important unit in ecology as well as
evolutionary biology.
– In ecology, species tend to have a functional role in a
community; i.e. as decomposers, producers, nitrogenfixers, parasites, etc.. This, and interactions with
other species such as competitors and predators,
largely define its ecological niche.
• Populations are groups of same species living in
the same place. This is the smallest unit that can
evolve. From an ecological point of view, most
intraspecific interactions (intraspecific
competition, mating, etc.) occur among members
of the same population.
– Populations may be structured; they may have
smaller subpopulations, or demes, which
interact and exchange members regularly, but
still most individuals tend to stay in a local
cluster of suitable habitat.
• Communities are populations of different species living in
the same place.
•
Ecosystems are communities of living organisms
considered in the context of the important nonliving
(abiotic) aspects of the environment. The biosphere is a
single, global, ecosystem.
Pattern, Process, Scientific Method
• Pattern- is what we observe;
– I.e., vegetation zonation, species lists, association of certain
species, population densities, behavior of animals.
• Process is the set of underlying mechanisms that produces
the pattern;
– I.e., nutrient cycling, herbivory, competition, predation risk,
nutrient availability, patterns of disturbance, energy flow, history.
What we see.
• Observation and experiment are both essential to any
science.
– Ecologists describe ecological systems (observation), then seek to
explain the underlying mechanisms that create them, maintain
them, and determine their fate.
• To explain ecological systems, ecologists develop
models-descriptions of the system, its components, and
its processes.
– Models are frequently simplifications of real world-no model is
perfect.
– The best models generate testable hypotheses.
– When a model’s predictive powers fail, it is either modified or
discarded. If a model survives multiple experimental tests, it is
said to be accepted, but it is never really proven.
• Ultimately, ecologists seek general theories with
predictive power.
– A series of models which is generally accepted is sometimes
called a scientific paradigm. These typify a mature science,
and direct ideas for future research.
• In many ways, ecology lacks a central paradigm, because some of its
central models and ideas are still disputed.
Example of an ecological hypothesis test
• Robert Marquis and Chris Whelan studied the role of birds in
limiting the density of herbivorous insects.
• They observed that deciduous forests harbor hundreds of species
of herbivorous insects, yet only a small proportion of total leaf
area is eaten every year.
• Many species of birds are insectivores, but spiders,
parasitic wasps, and fungal infections also attack insects.
Are birds an important factor in controlling herbivores?
• Experimental Treatment-Multiple trees
(replication is important) are enclosed in
cages to exclude birds but not insects.
• Control Treatments– ”Control trees” paired with the
excluded trees control for
environmental variation.
– Incomplete cages-control for the
presence of the cage.
• Data Collected– % of leaf area eaten
– density of herbivorous insects
• Prediction-if birds are an important
agent of insect control, both variables
should be higher in exclusion cages
Result
• Caged trees had 70% more insects than
controls, and caged trees had an increased
percentage of missing leaf area (35%)
relative to control trees (22%)
• Conclusion-birds are an important potential
agent of herbivore control.
• Other studies– One of the most important attributes of a good
experiment is that its results be reproducible.
– This is a problem in ecology, because
conditions in “the field” vary from year to year
and place to place-it is almost never possible to
reproduce a field experiment exactly.
– Exclusion experiments of this type have been
done many times, with different results
Ecological Time Scales
Ecological processes may occur over time scales ranging from
days to millennia.
The ecological time scale is shorter than the evolutionary time
scale, but there is some overlap-populations evolve over time, and this
can affect the composition of communities and functioning of
ecosystems.
• What we see today might reflect events that
happened long ago by our standards.
– Example-colonization of North American forests
following glaciation-a continuing process
• Alpine populations of tundra communities persist at high
elevations
• Chicago was under ice 15,000 years ago-“Lake Chicago”
existed here thereafter, gradually growing as the glacier meltedit drained out the Mississippi.
– As a result, The community of Great Lakes fish species resembles that
of the Mississippi river, rather than the Atlantic ocean.
• Deciduous trees have replaced Pine and Juniper as warm
conditions persisted– Different species have colonized at different rates.
– A relict population of Pines is still present at Indiana Dunes national
Lakeshore.
The Niche
• The niche is one of the most important concepts in
ecology.
– The concept of the niche overlaps so many different areas
Paradoxically, it is also one of the hardest to define (ecology
is still a young science) because different researchers have
different ideas of what constitutes a niche, and some have
argued that the concept has outlived its usefulness.
• Essentially, an organism’s niche is also defined by how
it makes a living; its role in the community, the
environmental conditions it tolerates, the important
resources it needs to survive, and its ways of obtaining
those resources.
– Thus, an organism’s niche touches upon its habitat, the
resources it needs, and its behavior.
• Two organisms cannot occupy exactly
the same niche.
– If this were to happen, inevitably, one would be a
better competitor for resources and ultimately
displace the other
• This is called the competitive exclusion
principal.
– It assumes that competition is a major interspecific
interaction between the species-in the absence of
competition there is no competitive exculsion.
– Experiments by Gausse (Paramecium), Peter Frank
(Daphnia), and Thomas Park (Triboleum) have
confirmed it for simple laboratory scenarios.
The “Hutchinsonian” Niche
• The ecologist, G. E. Hutchinson, brought the
niche concept a step farther.
– He defined the niche as “an n dimensional
hypervolume, enclosing the complete range of
conditions under which an organism can reproduce
itself”
• In theory, all variables relevant to the life history of an
organism must be included, and each must be independent
of the others.
– This definition of the niche is inextricably linked to
the concept of competitive exclusion-no two species
should be able to occupy exactly the same niche
• Hutchinson assumed no
overlap was possible
– however, it can be shown
that there are several
cases where the niches of
two species can overlap.
• In case A, the niche of a
competitively superior
species is included within
the niche of an inferior
competitive
• In case B, the overlap is
small-the inferior of the
two competitors is
generally excluded from
that portion of the niche
• Fundamental Niche– this is the niche an organism would occupy in the absence of
competition, predation, and other biotic interactions that limit
the organism. An abstraction.
• Realized Niche– the niche an organism actually occupies in a given
environment. Possibly real, but very hard to measure in real
life.
Niche Partitioning and Diversity
• The niche concept can provide a framework
for understanding the total number of
species a community can support.
– As a new area is colonized, species are free
from competition, and they are close to their
fundamental niches.
– As the habitat fills up, competitive interactions
cause the realized niches of many species to
become smaller and more specialized
– Species that do not fit, either because they are
outcompeted or driven extinct by predation, go
extinct. This process is called species sorting.
Are Niches Real?
• Possibly, from a scientific standpoint they are an
interesting abstraction, but of limited practical value.
– This is because field ecologists can’t measure all
important variables, in fact there are always some
variables we don’t know exist.
– In practice, this concept has been helpful, however,
because it
• orders the way we think about the lives of organisms
• provides a framework for knowing how many
organisms a habitat might support.
• In reality, most organisms sort themselves
by three important variables
– where they live
– what they eat or use as a limiting resource (i.e.
nest sites)
– when they are using it