LECTURE #10: Factors Affecting Populations

TEXT: Hedrick, Chapter 9

Population Ecology - The scientific study of the interrelationships among populations of organisms, and between populations of organisms, and between populations and all aspects, living and non-living, of their environment.

Population Ecology is concerned with the factors that affect the distribution and abundance of populations.

Keep in mind the scale of what you are looking at…

temporal scale - means 'over time'. (i.e. populations will change over time)

spatial scale - means 'over space'. (i.e. populations will change dependent upon geography)

Factors that affect the distribution and abundance of populations may be either abiotic or biotic:

abiotic = not living

biotic = living

Example: Diagrammatic representation of the correlation between climate as reflected by average annual temperature and precipitation and vegetational formation types (Whittaker, 1970): (SEE ALSO FIGURE 9/9 IN TEXT- General association of vegetation patterns with moisture and termperature (Ellseth and Baumgardner, 1980)

A more specific example of this concept; the Alaska treeline and mild coastal temperatures:

More examples:

Figure 9.16 in your text : The percent of evergreen coverage on two transects of increasing soil pH at a site in northwestern Mexico (Goldberg, 1982)

Figure 9.13 in your text: The distribution of the desert pupfish in a stream originating from a hot spring (Brown, 1976).

Vegetation type affects the distribution of species (keep in mind that abiotic such a temperature and moisture, as well as other biotic factors such as competition, predation, etc. may be coming into play here…)

Another example; FIGURE 9.18 from your TEXT: The distribution of sea urchins and algae in a transect extending from the seashore (Kitching and Ebling, 1961)

For any given species to survive and reproduce in an area, the environmental conditions must fall within a given range.

What is a 'niche'?

Definition of Niche - The functional position of a population of organisms in its environment comprising the habitat in which the organism lives, the periods of time during which it occurs and is active there, and the resources that it uses there.

The classic example of the niche;

Defining the 'niche' of several species of Warblers (MacArthur, 1958):

Breaking down the niche (FROM YOUR TEXT, Hedrick, pages 143-144):

Ecological niche - The total set of environmental conditions necessary for the persistence of a species.

Fundamental niche - That domain in multidimensional space defined by the range of each environmental factor that allows the organism to persist.

denotes resources necessary for the species, such as food type, habitat type, temperature, moisture, etc. Along a resource dimension, such as habitat type, only a certain array of conditions will be suitable for and utilized by the species.

NOTE: IN MANY CASES, THE SPECIES MAY NOT ACTUALLY EXIST IN ALL ENVIRONMENTS THAT COULD POTENTIALLY SUPPORT IT)

Realized niche - The conditions/space in which a species actually does exist.

Species will have an actual distribution which reflects the many factors that limit its potential distribution:

Swimming speed in Goldfish:

Clutch size in bird species:

THE BIG PICTURE:

Keep in mind that for any given population of study, there will be a number of biotic and abiotic factors that affect its distribution and abundance.

Examples: