BIO 3040 Principles of Ecology, Dr. L. Kelly
Chapter 9 -- Population Distribution and Abundance
Geographic ranges largely influenced by climate
Habitat heterogeneity affect species’ distributions
Biotic interactions can affect species’ distributions and population size
Ecologists use population data to help manage species
I. Distribution and spacing
A. distribution = geographic range of a species;
1. influenced largely by abiotic or physical (esp. climate) factors:
2. biotic interactions may be important
3. animal examples -kangaroos and tiger beetles -- Figures 9.2 & 9.3, p. 204;
competition between barnacles – Figures 9.8 & 9.9, p. 207
Areal extent of a species' distribution can be enormous for migrating birds and
other species that move seasonally or annually.
4. plant example -- Encelia spp. -- Figure 9.5, p. 206
Encelia californica & E. actoni have diff. macroclimates
5. environments largely heterogeneous:
Rarely are environments homogeneous
Therefore, we can recognize:
a. habitat patch = habitat of 1 type surrounded by
b. microenvironment -- e.g., Encelia spp., Figure 9.7, p. 207
E. frutescens & E. farinosa have overlapping distributions but occupy diff
microenvironments;
diff. adaptations to heat
c. density = # of individuals per unit
e.g.,
-- reflects both habitat quality & net movement of individuals
-- generally greater where resources are greater
important for management and conservation
B. Distribution among habitat patches
1. source population = population produces surplus offspring who
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2. sink population = population is maintained by immigration;
Dispersal is generally one-way -C. dispersion = spacing of individuals of a population with respect to
1. 3 main patterns: clumped, regular, random
at small scales; caused by abiotics and/or interactions: attract, repel, ignore
Figure 9.10, p. 208
2. patterns detected depend on size of area studied
3. pattern may change over time
example -- creosote bush, Figure 9.13, p. 210
II. Density declines as body size increases
III. Rarity and extinction (Figure 9.22, p. 218)
A. All species go extinct
B. Rare species -- more vulnerable to extinction
C. rarest -- restricted geographic range, narrow habitat tolerance, small local
population size
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