Biology Lecture 17
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Biology Lecture 17
Biology Lecture 17 on populations
What is population and what does it suggest?
Individuals of the same species in a given area at a given time
Suggests that space and time are importatnt components
What are 5 attributes of population?
Size - numbers (rarity, commonness)
Density - distribution in space (per unit area or volume)
Change in size over time ( increases/decreases in numbers, range)
What is range?
Overall Distributions in space - areal extent of a population or species
Name a species whoes range has expanded?
What do transplant experiments test? (2 things)
wehter a popluation
1. never disperse there
2. Can't survive there
What are 3 patterns which populations are distributed within their ranges?
Clumped or aggregated
Evenly or overdispersed
What are the hypotheses for the distribution patterns?
Clumped - resources clumped, social interactions, limited dispersal from parents
Random - random dispersal, resources
Even - Resources even, territorial interactions, competition
What is the definition and process of a random distribution?
An individual has an equal probablitlity of occurring anywhere in an area
netral interations between individuals and between individuals and local environment
What is the definition and process of regular distribution pattern?
Individuals are uniformly spaced through the environment
Antagonistic interactions between individuals or local depletion of resources - territoriality, competition, allelopathy
What is the definition and process for a clumped distribution?
Individuals live in areas of high local abundance, which are separated by areas of low abundance
Attraction between individuals or attraction of individuals to a common resource - sociality, resource clumping
How can the distribution of creosote bushes change through time? (3 steps)
1. Small shrubs establish in high densities and produce a cclumped distribution
2. Mortality as the shrubs grow reduces clumping and produces a random distribution amond medium shrubs
3. Competition enforces a regular distribution among large shrubs
How are body size and population size related?
Because larger body size requires more resources such as food, space, etc. Then we expect that body size and population size should be negatively correlated
Regressions of body size and population density of plants and animals support this prediction.
Who should know how population numbers change over time?
Economists, planners, farmers, insurance companies, school boards
what is the basis for population growth?
species interactions, evolution, etc.
What processes affect population size? ( 3 things)
1 Birth rates +
2. Death rates -
3. Immigration + , Emigration -
What is r in a population equation?
(birth rate - death rate) or (b-d)
What is N in a population equation?
What is the equation for exponential growth?
dN/dt = rN
Or the change in numbers (dN) over time (dt) is equal to the growth rate (r) times the number of individuals (N)
What is dN in the equation dN/dt?
Change in number
What is dt in the equation dN/dt?
Change in time
What 3 things prvents continued exponential growth?
External ( density independent factors)
- weather, huricanes, floods, drought etc.
- catastrophic events
Self regulation (density dependent factors)
- Resources becoming limiting ( competition)
- Toxic build - up
Interactions with other species (density dependent factors)
What is K in a population equation?
Carrying capacity of environment.
Explain the logistic or S - shaped growth?
begining of time b>d, r>0
Middle of time = maximum exponential growth
end of time Growth rate slows (b + d) or (r =0)
What is another way to put dN/dt
r((K - N) / K)N or (1 - N/K)
What is ((K - N) / K)?
a term that slows growth as N approaches K, the carrying capacity or is equivalent to a competition term
What is intraspecific competition?
The effect of individuals in a population on other individuals ( instantaneous effect )
Acts to decrease birth rate or increase death rate
What is intraspecific competition in the logistic equation?
((K - N) / N) or (1 - N/K)
What shape does a density dependent graph have?
What shape is a populaaion graph that is density independent?
What are 5 population features?
Growth of populations in ideal environments can be described with what growth model?
exponential growth model
What growth model shows a population in a limiting environment?
a logistic growth model