BIOL 1108 Chapter Notes - Chapter 46: Metapopulation, Parasitism, Biogeography
Core Concepts
• A population consists of all the individuals of a given
species that live and reproduce in a particular place.
• Population size can increase or decrease over time.
• The age structure of a population helps ecologists
understand past changes and predict future changes in
population size.
• The dynamics of populations are influenced by the
colonization and extinction of smaller, interconnected
populations that make up a metapopulation.
• If a population starts with 80 individuals and grows to 120
after two years, what is the population increase per year?
Change Over Time
The population has gained 40 individuals in two years (20 individuals/year)
In our example above, r equals 20 individuals per year divided by
80 individuals, for a per capita growth rate of 0.25 per year.
• What is the Growth per capita? r = (ΔN/Δt)/N1
• What is the Per capita growth rate over time? Nt = N1(1 + r)t
Using 10 years as our example: Nt = (80) (1 + 0.25)10
N at time 10 = 745
In 10 years, this population, as presented, will have
grown to 745 individuals from 80.
Exponential growth is not sustainable
• Resources will run out
• This promotes intraspecific competition
• Which results in natural selection
• Interspecific competition will also affect
population size
Limiting factors keep growth in check
• Density-Independent Factors – Limit populations regardless of population density – Droughts
or other severe events – Environmental conditions (temperature, light
availability…)
• Density-Dependent Factors – Competition for limited resources – Predation, Parasitism –
Diseases
Even for simple models, ecologists use sampling
methods to estimate population size & density
• Census: count every individual (usually not practical!)
• Sampling: Plots or transects to count individuals in a smaller area;
trapping or fishing; or less direct methods like counting tracks or songs
• Mark-and-Recapture: Catch, mark, and release individuals, then sample
again and use some math & probabilities to estimate total density
Population Demography
• Population ecologists use
Document Summary
The population has gained 40 individuals in two years (20 individuals/year) In our example above, r equals 20 individuals per year divided by. Using 10 years as our example: nt = (80) (1 + 0. 25)10. In 10 years, this population, as presented, will have grown to 745 individuals from 80. Exponential growth is not sustainable: resources will run out, this promotes intraspecific competition, which results in natural selection, interspecific competition will also affect population size. Limiting factors keep growth in check: density-independent factors limit populations regardless of population density droughts or other severe events environmental conditions (temperature, light availability , density-dependent factors competition for limited resources predation, parasitism . Population demography: population ecologists use demography the study of statistics such as birth rates, age or size structure, and distribution over time (and sometimes across environments) The pattern of investment in growth vs. reproduction vs. survival over an organism"s lifetime is called its life history.
