Ecology, its Scope, its Methods, its Goals

Reading: Smith and Smith, Chapter 1-read, Chp 14, pps 257-263-read

carefullyWho 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, nitrogen-fixers, 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 ScalesEcological 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 melted-it 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