Lecture 7: Density Dispersion Demographics Flashcards
What is population ecology
Explores how biotic and abiotic factors influence the abundance dispersion and age structure of populations
ex. the number of turtle hatchlings that survive their first journey to the ocean is affected by both predation and light
Define population
a group of individuals of a single species living in the same general area
ex. Members of a population can be vague, people in a grocery store at a given time, students who attend UCR, people in southern California
What are the four emergent properties of population –
size, density, dispersion, and rate of change
What adds to the population size
births and immigration
What removes individuals from the population size
deaths and emigration
How do we measure density
A) Count
B) Count subsamples and extrapolate
C) Mark - recapture
D) Use proxy, nests, feeders, tracks
Why do scientists choose to use estimates or proxy measures or density instead of counting all individuals
Estimates and proxy takes less time, helps scientists to avoid disturbing fragile ecosystems
How are the individuals in the population distributed over the landscape or in the water column?
RANDOM dispersions
What are the causes of random dispersions which are very rare in nature
Caused by unequal distribution of resources, dispersal probabilities
ex. two toed sloths, some spiders
What is clumped dispersion
Individuals are more aggregated than in a random distribution
Causes: Resource availability, mating behavior, and group defense against predators
What is uniform dispersion
Individuals are more evenly spaced than in a random distribution and individuals are less likely to be found in close proximity to other individuals
Causes: (negative) social interactions, (territoriality - define of bounded space against other individuals), competition
What is demography
stdy of the vital statistics of a population and how they vary with age
What is a life table?
Age specific summary of the vital statistics of a population
What is a cohort
A group of individuals in a population born about the same time
What is survivorship (Ix)
Proportion of individuals born that survives to age x
What do survivorship curves show us
The data from life tables
What is a reproductive table
An age specific summary of the reproductive rates in a population
When is reproductive value the highest
usually highest at the peak reproductive period
What is a life history?
and size of offspring
The schedule of an organism’s life:
- age/size at reproductive maturity
- allocation of energy to reproductive
- number and size of offspring
- number of reproductive events
- life span
R-selection in the central trade-off: reproductive strategy
Selection for life history traits that maximize reproductive success in uncrowded environments.
K-selection in the central trade-off: reproductive strategy
Selection for life history traits that are sensitive to population density.
what is demography
rate of change in a population size over time (growth, decline, or stability)
dispersion
distribution of individuals in the population over space or volume
density
number of individuals per unit area or volume
Population size is ____ - _____
births + immigration - deaths - emigration
