Population Ecology I - Distribution and Abundance Flashcards
Population
individuals of the same species that co-occur in space and time
Characteristics of Populations:
- density: number of individuals
- distribution: size, shape and location of area occupied
absolute density
the number of individuals of a population per unit area
ecological density
the number of individuals of a population per unit SUITABLE HABITAT
What is a metapopulation
a group of subpopulations living on such patches by exchanges of individuals make up the metapopulation
essentials of metapopulations
- are a population of subpopulations
- subpopulations are connected by movement of individuals from one subpopulation to another
- any subpopulation can go extinct and be re-colonized repeatedly over time
- the risk of subpopulation extinction is generally greatest for small subpopulations
- density-dependent and density-independent population dynamics occur within each populaiton
Distribution
the geographic distribution of a species is limited by the physical environment (incl. both abiotic and biotic conditions) and species niche requirements
What influences population distribution and abundance?
- habitat suitability
- historical factors
- dispersal limitation
Dispersal
the permanent movement of individuals (or propagules), usually from population to another
Why disperse?
to avoid inbreeding
- natal dispersal: juveniles undergo permanant dispersal to another location
Seed Dispersal Modes
- gravity (short)
- explosive (short)
- by wind (short-to-long)
- water (short-to-long)
- animals (via ingestation and defecation, short-to-long distance)
Two major categories of dispersal
- immigration: movement into a local population
- emigration: movement out of a local population
Drivers of Numerical Responses
- reproduction: lag time needed for predators to produce offspring
- dispersal: no lag time as species are highly mobile and can track prey across the landscape
Random distribution
- individuals have an equal chance of living anywhere within an area
- results from neutral interactions among individuals of a species, random disturbances, uniform disturbances of resources
Regular Distribution
- individuals are uniformly spaced
- results from antagonistic interactions among individuals of the same species, uniform distribution of resources, uniform depletion of resources
Clumped distribution
- individuals have a higher probability of being in some areas versus others
- results from mutual interactions, patchy resources, dispersal limitations
Large Scale Distributions
how populations are distributed over scales in which there is significant environmental variation
On larger scales, what kind of dispersion pattern do many animal and plant species show?
clumped
Broader niche usually indicates?
a wider species large-scale distribution
Why aren’t all species in all the places?
- principle of allocation
- takes extra energy to survive and reproduce in regions on the edge of their niche
- surviving at the edge of tolerance is not efficient
Example of Range expansion in Invasive Species
Africanized bee -hybrid between european bees and african honeybee
- stopped spreading in 2009
- too cold both north and south of their range
relationship between organism size and population density
population density declines as organism size increases
why does does the relationship between organism size and population density occur?
- body scaling
- metabolic demand vs. resource availability