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BIOL215 Lecture 21 Notes.pdf

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McGill University
Biology (Sci)
BIOL 215
Neil Price

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 habitat 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 rate/generation • 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) • Typically in island colonisations • Secular dispersal (the diffusion over evolutionary time scales) • The Ilamas and vicunas of South America are descended from now extinct North American members of the camel family that migrated during the Pliocene over the Isthmus of Panama • Not very important to ecologists because it has to do with evolutionary time scales Some organisms do not occupy all of their potential range even though they are able to disperse into unoccupied areas Three basic biotic limitation on geographic distribution: • Behavioral responses to habitat selection - behavioral trait which evolved • Marine invertebrates have a larval stage that actively selects suitable substrate • Competition and predation may limit colonization success • Studied in marine system because they are easy to manipulate • Allelopathy - production by cer
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