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BIOL 215 Lecture Notes - Herbivore, Environmental Factor, 30Th Parallel North

Biology (Sci)
Course Code
BIOL 215
Neil Price

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BIOL215 Lecture 21 Notes
Ecology - study of the distribution and abundance of living organisms
Grey wolf example is found in northern hemisphere, but have small pockets in other areas
Practical value of knowing the limits to species distribution (i.e. invasive species through human
travels) - is useful to know the limits of the distribution of these species may be when it gets to a new
African bee which was brought into Brazil to improve honey production escaped and started to
spread into the tropical rainforest and become a competitive dominant and its displaying the native
species which help pollinate the vegetation found in rainforest. It's spread into North America will
cause additional economic damage since honey bees are important to pollinating our crops
To find out the geographic limits of various species, you can conduct a transplant experiment
which deliberately moves a species from their normal range to
areas where they are not found and ask the question: Can they
survive in those regions or is dispersal a problem where they
cannot reach those areas in the first place?
Transplant successful: distribution limited either because the
area is inaccessible, time has been too short to reach the area,
or because the species fails to recognize the area as suitable
living space
Transplant unsuccessful: distribution limited either by other
species (biotic) or by physical and chemical factors (abiotic)
Dispersal limitation on geographic distribution is important part of
establishing species limit. It is particularly the case during range
expansion, but dispersal also occurs among individuals within populations looking for food and for
exploiting resources as they become diminished in their current habitat
Dispersal is difficult to study because it may involve a chance event. Species that disperse may not
colonize. Results in gene flow that affects the genetic structure from one population to another
Three main modes of dispersal:
Diffusion (movement of individuals across a hospitable environment expanding their range slowly)
which is distance moved = D*N*sqrt(ln Ro)
Where D - avg. dispersal distance, N - number of generations, and Ro - reproduction
Most seeds fall near the parent tree, but rare and extreme dispersal events are important and
difficult to observe
Reid's paradox - if you look at average dispersal distance, you cannot predict very well the
range at which a species will expand its range into hospitable territory; rather, the rare
occurrences where species are transported to great distances but infrequently are very
important in determining the range expansion, especially in trees
Jump dispersal (the movement of individuals across large distances which are usually inhospitable
terrain to a habitat that allows the organism to survive and reproduce)
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