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Lecture 8

Biology 2483A Lecture Notes - Lecture 8: Semibalanus Balanoides, Desert Pupfish, Monarch Butterfly

Course Code
BIOL 2483A
Hugh Henry

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a group of interacting individuals of the same species living in a particular area.
Interactions within populations include sexual reproduction and competition.
Populations are dynamic - distribution and abundance can change over time and space. Understanding the factors
that influence these dynamics helps us manage populations for harvest or conservation.
Population :
Geographic area where individuals of a species occur.
Number of individuals in a given area.
Example: On a 20-hectar island there are 2,500 lizards. Population density = 125/hectare.
Sometimes the total area occupied by a population is not known.
It is often difficult to know how far organisms or their gametes can travel.
When the area isn't fully known, an area is delimited based on best available knowledge of the species.
Abundance can change over time and space
Insects live in goldenrod. The dots represent sites where they sampled abundance over time. Focus on the
red dots…
Lecture 8: Population Distribution and Abundance
Thursday, October 8, 2015
1:51 PM
Lecture Slides Page 1

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When you look at the densities over time you really don't see a nice correspondence. There is a lot of
variability along one site. So climate is not the only factor on abundance.
In plants, dispersal occurs by seed movement. The distance moved can be very small.
Other species, such as whales, can move thousands of kilometres in a year.
Species vary in their ability to disperse.
Some populations exist in isolated patches that are linked by dispersal.
Example: heathlands in England have been fragmented by human development.
This can result from physical features of the environment, or human activities that subdivide populations.
Budding: asexual reproduction in which a new organism develops from an outgrowth or bud due to cell
division at one particular site. The new organisms remains attached as it grows, separating from the parent
organism only when it is mature, leaving behind scar tissue.
For some species its hard to determine what an individual is:
Lecture Slides Page 2

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Apomixes: unfertilized egg that develops into a new organism.
Horizontal Spread: the root spreads horizontally and the new shrub grows.
If member of a genet are independent physiologically, each member is called a ramet.
Distribution and Abundance
Abiotic features: Moisture, temperature, pH, sunlight, nutrients, etc.
Some species can tolerate broad ranges of physical conditions, others have narrow ranges.
Habitat Suitability
Creosote bush is very tolerant of dry conditions and occurs widely in North American deserts.
Saguaro cactus can tolerate dry conditions, but not cold temperatures and has a more limited
Lecture Slides Page 3
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