and the
Scientific Method


Study of the Relationship Between Organisms and Their Environment

  • Ecology was thrust into the limelight in the late 1960s and early 1970s.
  • April 22, 1970
  • Ecology is a very integrative science
  • Ecology is the scientific study of the relationships between organisms and their environment.
  • Functional definition of ecology:
  • Haeckel related ecology to the new and revolutionary ideas put forth in Charles Darwin's The Origin of the Species (1859)
  • Darwin's theory of natural selection is a cornerstone of the science of ecology
  • Natural selection


The Development of Ecology

Plant Geography

  • Plant Geography: primary parent of modern ecology
  • Early plant geographers such as Willdenow, and Humboldt:
  • The study of plant communities developed along different paths in Europe and America
  • In Europe plant ecologists concentrated on describing plant communities.
  • In America plant ecologists were far more interested in how plant communities develop


Population Ecology

  • In developing his theory, Charles Darwin (1809-1882) was influenced by the writings of Thomas Malthus (1766-1834).
  • From this concept Darwin developed the idea of "the survival of the fittest" as a mechanism of natural selection and evolution
  • Unknown to Darwin, an Austrian monk, Gregor Mendel (1822-1884) was studying in his garden the transmission of inheritable characters from one generation of pea plants to another
  • Population ecology is concerned with:
    • .........
    • .........
    • .........


Ecosystem Ecology

  • Early ecologists were concerned with:
    • observing the patterns of organisms in nature
    • attempting to determine how patterns were formed
    • how are patterns maintained by interactions with the physical environment
  • Later, ecologists began to look at energy flows in ecosystems:



Ecology is an Empirical and Experimental Science

  • Early on, ecology was largely observational and descriptive
  • In North America
  • In Europe
  • Early steps at empiricism in North American ecology began with F.E. Clements (1874-1945)
  • Empiricism is .............................
  • Clements studied development of vegetation in the Midwestern grasslands
  • Clements devised the quadrant method which is still used today
  • The establishment of permanent plots allowed the study of
    • the development of vegetation or succession on denuded plots
    • the changes in plants in response to environmental changes
    • the changes in plant communities across a gradient
  • By the 1960s mathematical models were being developed and that helped bring to ecology a strong emphasis on
  • The specific goal of ecology is to understand the patterns and processes related to life on earth
    • how the variety of plants and animals have adapted to the various environments and how they interact among themselves and with the abiotic environment




  • Inductive method: the scientist gathers empirical data and from it arrives at a generalization
  • Deductive method: a scientist develops a general idea about a phenomena, performs experiments and from them makes specific predictions that can be tested again


  • The inductive approach is the formation of general principles from specific observations
  • The deductive approach is the prediction of specific events from general principles



Experimental Approach

  • Ecologists employ direct observation and comparison in "natural experiments".
  • Example: Dead Trees/Woodpeckers
    • The observed patterns only suggest a correlation (co-related)
    • They do not address the question of cause and effect
    • This rigorous establishment of causation is what separates science from unwarranted assumptions about reasons for observed phenomena.





  • The experimental approach, unlike the collection of observations from unmanipulated systems, directly determines the response of one variable -- the dependent variable -- to variation in some other variable(s)-- independent variables.


  • One source of variation very difficult to control is the inherent genetic variation among individual organisms in a population.
  • replication
  • replicates


  • Because the purpose of the experiment is to examine the response of the individuals or experimental units to the treatment (variation in the independent variable) , a group of individuals must be used as a control.
  • In the case of the experiment to examine the response of plants to elevated CO2, the investigator would grow the control individuals under current normal (ambient) concentration of CO2, thereby providing an estimate of (expected) growth for individuals in the population under baseline conditions.


Field Experiments

  • Lab experiments......
  • Field experiments involve the manipulation of one or more independent variables in a natural system
  • This comparison will form the basis for testing the hypothesis regarding the influence of the independent variable on the dependent variable.



Hypothesis Testing

  • Assume the investigator has developed a hypothesis that elevated levels of CO2 result in increased plant growth.
  • Plant growth response to elevated CO2 is the dependent variable and the concentration of CO2 is the independent variable.
  • The investigator wants to know the effect of varying the independent variable.
  • The next step is to collect the data necessary to test the hypothesis and reach a conclusion.
  • The experimental data would consist of growth measures (e.g. biomass gain over a period of time) for plants grown under ambient (the control samples) and elevated levels of CO2 (treatment samples)


  • We test the hypothesis statistically by creating a
    • null hypothesis (H0) and an
    • alternative hypothesis (H1)
  • In the present experiment the null hypothesis would state that the elevated levels of CO2 have no effect on growth, because generally in an experiment it is easier to disprove a null hypothesis than to prove a hypothesis.



Models & Predictions

  • After hypothesis testing, we can formulate a relationship between a dependent and independent variable (for example, plant growth and the level of CO2) to develop a model of how this two-variable system functions.


  • We can view hypotheses as models
  • Models can be statistical or nonstatistical.