Biology 2483A Study Guide - Final Guide: Aspen Grove, Habitat Fragmentation, Hectare

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Published on 15 Dec 2017
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Unit 3: Populations
Chapter 9: Population Distribution and Abundance
Population: group of interacting individuals of the same species living in a particular area
oInteractions within populations include sexual reproduction and competition
oAre 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
Distribution: geographic area where individuals of a species occur
Abundance: number of individuals in a given area
oCan be reported as a population size (number of individuals) or density (number of individuals per unit
area)
E.g. on a 20 hectare island there are 2500 lizards  population density = 125/hectare
Sometimes the total area occupied by a population is not known
oOrganisms are sometimes mobile
oIt is often difficult to know how far organisms or their gametes can travel
oWhen it isn’t fully known  area is delimited based on best available knowledge of the species
Abundances
Abundance can change over time and space
oBlue dots = sampling the abundance of organisms
oRed dots = relatively close region  expect climate to be similar
When we look at densities over time there isn’t a ice correspondence
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Lack of synchronism indicates that climate is not the only factor influencing population
density
Dispersal
Species vary in their ability to disperse
In plants dispersal occurs by seed movement (distance moved can be very small)
Other species such as whales can move thousands of kilometers in a year
Some populations exist in isolated patches that are linked by dispersal
This dispersal can result from physical features of the environment, or human activities that subdivide
populations
oE.g. heathlands in England have been fragmented by human development
Individuals
For some species, it’s hard to determine what an individual is e.g. Aspen (below) have same genetic individual
but buds come up and give rise to new stems. They are not independent trees
Some plants and animals form clones:
Individuals can be defined as products of a single fertilization e.g. the aspen grove would be a single genetic
individual or genet
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If members of a genet are independent physiologically, each member is called a ramet
For instance, in bottom strawberry branch, the genet consists of that original ramet which grew from a seed.
The bunch a slight distance away is a genetically identical daughter ramet produced from a bud on a horizontal
stem
Distribution and Abundance
Distributions and abundances of organisms are limited by habitat suitability, historical factors, and dispersal
Habitat Suitability
Abiotic features: moisture, temperature, pH, sunlight, nutrients
oSome species can tolerate broad ranges of physical conditions, others have narrow ranges
E.g. Cresosote bush is very tolerant of dry and cold conditions and occurs widely in North
American deserts
E.g. Sanguaro cactus can tolerate dry conditions but not cold temperatures and has a more
limited distribution
Biotic features: organisms are affected by herbivores, predators, competitors, parasites, and pathogens
oE.g. in Australia, an introduced cactus became a pest species, spreading over vast areas. A moth that
feeds on cactus was then released, and distribution and abundance of the cactus had been greatly
reduced
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