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BIOL 4120 Principles of Ecology Phil Ganter 301 Harned Hall 963-5782 |
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Restinga
Jurubatiba in Brazil
The restinga biome (a tropical dune forest) is both valuable, because it contains a diversity of valuable plants and animals, and disappearing. The restinga is part of the Atlantic Coastal Forest biome in Brazil, one of the most diverse terrestrial plant communities. Less than 10% of the original area occupied by this biome is unaltered by man |
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Lecture 1 Ecology as a Science
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Overview - Link to Course Objectives
General Ideas about Ecology
- definition
- Importance of Ecology
- Status of Ecology
Some General Ideas about Ecology
Ecology is the study of the abundance and distribution of organisms
To study these things, ecologists must account for all influences on abundance and distribution (in both space and time), and these influences include both abiotic (geography, climate, etc.) and biotic (other organisms from the same species, from other, related species, from unrelated species) components
REMEMBER THAT THE ENVIRONMENT OF AN ORGANISM INCLUDES BOTH LIVING AND NON-LIVING COMPONENTS
Ecology has important impacts on everyone's daily lives
Globally, human populations have grown to the size that we can alter the natural environment over large geographical areas
Global warming, Loss of ozone protection, Loss of important marine fisheries
Locally, ecological decisions affect how we live in Tennessee and Davidson County
data is needed to assess the impact of road building on living in the Nashville area and to bring local and state agencies (and local businesses) into compliance with state and federal regulations concerning the environment
Ecology is not something one can avoid even though one may attempt to ignore it
if you breath, eat, drink water (or beverages composed mostly of water), are affected by the weather, or are likely to get sick some time in you life then you will depend on a natural system to supply a necessity. If you live on Earth, then that natural system is being directly or indirectly affected by the human population (and the indirect effects are rapidly dwindling as man directly affects more and more remote ecosystems).
Large Scale Ecosystem Services:
Direct: Water supply, Oxygen supply, Food supply (oceanic fisheries, pollination, natural pest predators), Extractive renewable commodities (wood, some fuels, some fertilizers), Genes (increasingly important as our ability to manipulate genes increases), Recreation
Indirect: Nutrient cycling, Atmospheric regulation (CO2, SO2, O3, NO3 levels), Climatic buffering (run-off control, heat dissipation, wind amelioration), Waste elimination (sewage, agricultural pollution), Erosion control
Ecology is a science (see next section), but has important interactions with all areas of human endeavor
ecology is the basis of environmental science (the study of man's effect on natural systems), conservation biology (the study of how to preserve natural systems undergoing human impact), restoration ecology (the study of means of restoring ecosystems altered by human activities to their pre-alteration state), and environmental engineering (the study of how we can manipulate the natural world to produce desired effects or to lessen the impact of disturbances caused by human activity)
ecologists interact with economists (to determine the costs of environmental change), with engineers (to predict and modify the effects of human activities), with sociologists and anthropologists (to understand how human society views, uses, and affects the natural environment), and with ethicists and theologians (about the basis of ethical behavior)
be sure to read the text about an attempt to value (in terms of dollars) the services we get from the ecosystems in which we live.
Ecology is a changing body of knowledge
as with all sciences, conclusions are reached on the basis of data
ecological data are often difficult and expensive to collect and interpret. Studies are often not conclusive or cannot be generalized. When a decision must be made on the basis of inconclusive data, it is often open to criticism.
Ecology is organized into a hierarchical group of subdisciplines
Behavioral ecology is the study of how behavior of individuals affects their ability to survive and reproduce. Since a population is composed of individuals (usually but not always - ask me in class what I mean by this) behavior directly impacts population level phenomena, such as population growth rate
Autecology (or Physiological Ecology) is the study of how physical factors; such at temperature change, seasonality, soil nutrient composition, affect the survival and reproduction of individual organisms
notice that, in both of the definitions above, the focus is on what affects survival and reproduction, the core determinants of success or failure for individuals and populations. This focus is what makes these studies ecology and not behavioral science or physiology
Population ecology is the study of how groups of individuals (belonging to the same species) grow (or shrink) and exchange individuals with other populations nearby. Depending on the nature of the species, many factors may affect population growth (food availability or quality, predators, habitat change, etc.)
The evolutionary history of the population is also important in that the species of grass in the study react differently to the presence of the toxin-producing species if they have experienced this toxin in the past (note that the Caucasian grasses both grew better than the native Montana grasses in its presence but they also did not benefit from the removal of the toxin by adding charcoal to the soil). Thus history and evolution are integral parts of ecological studies in that a grass from Montana reacted differently than one from the Caucasus region (contrast this with chemistry, in which one does not have to know where a molecule of glucose came from to know the properties of the molecule).
Evolutionary biology has a subdiscipline, Population Genetics (rather incorrectly called evolutionary ecology in Smith and Smith), which studies the change of a population of organism's genetic makeup. Population genetics studies all of the forces (including natural selection) that can change the frequency of a gene in a population of organisms. Because it also deals with populations, it is sometimes combined with Population Ecology into a single area, Population Biology. It is a natural marriage because the ecological circumstances that affect the ecology of a population do so because they affect the probability of surviving and reproducing. These probabilities are also the basis of evolutionary change and that ties the two subjects together. Where they differ is in the unit studied (the gene or the individual) and, to some extent, the time scale (long for population genetics, shorter for population ecology)
Community ecology is the study of how populations from different species interact to mutually affect each population's growth and survival. What composes a community is very changeable and depends on the organisms studied and the purposes of the investigator. The only commonality is that the different populations (representing different species) must interact with one another. Often, they will be similar species (e. g., the trees in a forest) as their similarity means they have similar habitat requirements and, most probably, will interact because of those needs.
Ecosystem ecology is the study of how the flow of energy and matter in large scale living systems. Ecosystem ecology is concerned with how nutrients enter, are recycled within, and leave the system; with what inputs of energy do the work in the system, how that energy is passed from one part of the system to another, and how energy leaves the system. Typically, the community studied in ecosystem ecology encompasses all organisms that are a part of the system. However, the emphasis is not on the organisms as much as it is on the flow of materials and energy between them.
Landscape Ecology - Ecosystem ecology has been enriched with new types of data. At first, ecosystems data were usually measured as changes in biomass or nutrients or energy. Satellite cameras now give us data on changes in plant communities over large areas. Using different types of cameras yields data not only on vegetational changes but also on changes in productivity, temperature and other ecological parameters. Analysis of this data has given rise to a new subdiscipline, landscape ecology, which looks for matches between changing factors. Landscape ecology also has impacts on agriculture, where it has been used to assess the need for fertilizer and pesticide application.
Emergent Properties and Hierarchical Organization
A good question to ask at this point is why organize the field of ecology in such a manner. Why not just study how individual animals react to different factors and add up these responses in some fashion to predict what to expect from nature? The answer lies in the concept of emergent properties, of which we will hear more later on in the course. To understand this, you have to have a clear idea of what a hierarchy is. A hierarchy is a means of grouping units of something (individual animals, say) into nested levels of groups. Thus, in an organism, atoms are grouped into kinds of molecules, which are grouped into different kinds of organelles, which are grouped into different kinds of cells, which are grouped into different kinds of tissues, etc. This grouping is not just for convenience but is a real grouping (i.e. it exists in nature). The ecological hierarchy is real also, and we study it as such because some phenomena are only observable by studying a particular level of organization in the hierarchy. The set of phenomena that can be explained only by looking at a particular hierarchical level are the Emergent Properties of that level. We study populations, because one may not be able to understand why a species is rare just by looking at how many offspring an organisms can produce. The same reasoning leads us to consider community ecology as a separate subdiscipline, as it may be impossible to understand the change in one population without understanding its interactions with other species. So, we have a hierarchy of ecological subdisciplines because nature is hierarchical and there are phenomena that are understood only when one studies the appropriate level within the hierarchy. Finally, having argued for separate subdisciplines, I want to caution you about considering them as independent of one another. All belong to the same hierarchy.
Ecology employs the scientific method
the scientific method is a system of observation that is "formalized", which means that it is done is such a way that one can reproduce the observations under the same conditions. The ideal is that the method of observing must be specified in such a way that other laboratories can observe what another scientist reports. We will not go over the parts of the scientific method here, as you have already been exposed to them, but we will emphasize that the scientific method is the basic technique of ecology, as it is in all scientific fields.
Karl Popper proposed that scientific method could never prove hypotheses, but could falsify hypotheses. We accept a hypothesis as true because, after repeated attempts, no one could disprove it. You might hypothesize that roses are red and support this hypothesis by growing roses in your garden. You might do so for years and only get red roses, thousands of red roses. However, if, after decades of patient rose-growing, one rose opens and is white, your hypothesis is falsified. The thousands of red ones support the hypothesis but they do not prove it. The white rose falsifies it. By this interpretation of how science is done, only hypotheses that can be falsified are amenable to scientific study. Hypotheses that can't be falsified may be true but science can not assess their truth. This is a very short introduction to a very big subject and we will not discuss whether or not Popper is the final word on how the scientific method works (there are other ideas).
Ecology employs both theory and data
Understanding a phenomenon involves relating Data ("Just the facts, Mam.") with a conception of how the system works (a Theory or, if you like plain language, a story). Important theories tie together large sets of data. All understanding involves both of these. Chemistry depends on atomic theory, which ties together many observations in chemistry and physics into a picture of the atom and its properties. A Hypothesis is more narrowly focused than a theory and is usually confined to an explanation (or prediction) of the outcome of an experiment. Since many hypotheses have little data to support them, there is a huge gap between a theory and a hypothesis. The statement "it's just a theory" is equivalent to saying that the Pacific Ocean is "just a pond" when dealing with well-supported theories. The problem is that the term is often used when hypothesis is more proper. If I have an idea about something but little evidence to substantiate it, it is not my theory, it's my hypothesis. The first ideas about the impact of refrigerant gasses (CFCs) on the ozone layer were hypothesis. Now, we can speak of the theory of ozone depletion due to release of CFCs. The difference? Years of carefully collected data linking the presence of CFCs in the upper atmosphere to ozone breakdown.
Both theory and data are changed and added to or rejected as time goes on
You will often hear the word model used by me and see it in the text. In the context of ecology, a model is a explanation of why something happens. It can take the form of a statement (a hypothesis stated as a sentence is a short model, but a model all the same). However, it can take other forms. The two most commonly found in ecology are graphical models and mathematical models. Mathematical models are one or more math expressions (=equations) that can be used to predict the outcome from a set of initial conditions. Graphical models so the same, but the math is expressed as a graph, not as an algebraic expression. The advantage of using a graph or a set of expressions as a mode rather than just statements describing the idea l is that you must be very precise about the model. Thus, a mathematical model will make a prediction that can be checked against the data (and we can accept or reject it based on its ability to make accurate predictions). So, models often lead to predictions that can be used as hypotheses in experiments, linking them to the scientific method. Verbal models make predictions too, using logic, but the predictions are difficult to make verbally if one is predicting the amount of some outcome. Mathematical models naturally make predictions in amounts and, thus, often are easier to test.
Ecology employs experiments and non-experimental observations
because we cannot imagine all possible things and many of the things we imagine do not occur, ecology depends on observation of nature to generate a body of facts from which to deduce hypotheses
Observations are information recorded directly from nature without any manipulation of nature. If you go to a forest and map the trees present in it, you are taking observations. You did not plant the trees and so you are merely recording what nature has done.
Observational studies take a large set of observational data, point out patterns in the data (often by presenting the data graphically) and seek to explain the patterns with some logical scheme (a hypothesis).
Experiments, the basis of the scientific method, record facts that emerge only after the experimenter has manipulated the environment in some way. Experiments test hypotheses generated from data and produce new data so that new hypotheses can be generated. The generation of hypotheses is part of a scientists creativity. The other side of creativity is designing the experiment to test the hypothesis.
- experiments have some elements in common:
- Treatment Groups are the organisms that will experience something suggested by the hypothesis: e.g. if you are testing for the effect of an industrial byproduct on fish, the treatment group would be exposed to the byproduct
- Control Groups do not experience the treatment and are used to see what the outcome is without the treatment. They should experience all of the same conditions as the treatment group except the treatment.
- Repeatability is a necessary part of any experiment. If the same conditions and elements are present, the same outcome should occur. Often, treatments and controls are replicated within the experiment to satisfy this repeatability requirement. In addition, replications are needed to statistically evaluate the results of an experiment, as explained below
Ecologists employ several different types of experiments. The differences depend on the fact that manipulations done in a laboratory are most easily controlled and thus yield the most repeatable data, an important result in science. However, the laboratory is not as complex as nature and we really want to understand nature, not things in labs, so we move the experiments outside. However, outside we have far less control and things are less repeatable. To sum up, the lab is repeatable but not real and nature is real but not repeatable. We try to trade off these things when doing ecology.
Field Experiments -- often have more than one variable and controls are more difficult to define. Many non-experimental variables can not be kept constant, but are allowed to vary in a random way in all experimental situations. This means that one must have more than one replication of the experiment, so that one can see the response to the experiment is the same no matter what changes occur in the non-experimental variables.
Natural Experiments -- when a change occurs in nature, but the experimental variable is not controlled by the experimenter.
Snapshot Experiments - when different locations have different levels of a variable, then a snapshot of the locations at the same time can be compared to understand the effect of the variable
Trajectory Experiments - when the experimental variable is manipulated by a system perturbation (Hurricane Andrew is a good example), the before and after situations can be compared to understand the effect of the variable at the same place through time.
Laboratory Experiments -- manipulate an experimental variable and observe a response variable. Usually only one experimental variable, other variables are kept constant. Control situation, with no manipulation, used to observe the outcome of the null hypothesis
Phenomenological experiments - constructed to show that response A occurs after manipulation B and we conclude that B causes A
Mechanistic Experiments - constructed to explain why response A occurs after manipulation B and we conclude that B causes A by a particular mechanism
Terms
Ecology, Environmental Science, Conservation Biology, Environmental Engineering, Behavioral ecology, Autecology (or physiological ecology), Population ecology, Population genetics, Population biology, Community ecology, Ecosystem ecology, Landscape Ecology, Emergent Properties, Scientific Method, Karl Popper, Data, Theory, Hypothesis, Model, Graphical Model, Mathematical Model, Field Experiments, Natural Experiments, Snapshot Experiments, Trajectory Experiments, Laboratory Experiments, Phenomenological experiments. Mechanistic Experiments, Treatment Groups, Control Groups, Repeatability, replications,
Last updated January 9, 2007