L. 25 - Groups & Populations Flashcards
L.O.
- Be able to describe and understand exponential and logistic models of population growth
- Define instantaneous growth rates in discrete and continuous exponential growth models
- Become familiar with demographic rates and how they are measured
- Understand what a stage/age structure model is
- Understand what a spatially structured population is
- Understand the principles and implementation of population viability analysis
Groups
- Multiple organisms of some or different species in a common space
- Ephemeral or consistant
- Social, indirect or accidental
Populations
A number of organisms of same species in a defined geographical area
- Populations can move geographical locations or stay put
Properties of populations
- number of individuals/ population size
- Area they occupy
- Age structure
- Sex ratio
Populations are essential for
Ecology:
- Distribution and abundance of individuals and how it might change
- Densities
Evolution:
- Populations of organisms evolve, not individuals
- Gene flow
Conservation management:
- Invasive species
- Defining threat status
- Translocation and restorations
Population biology
- Understand temporal dynamics of populations
- Understand spatial distribution of a population (in some areas but not others)
Population growth
- Change in numbers over time (positive or negative)
- Rate (r) = change/ unit of time
Demographic rates:
Variables that drive changes in populations
- Birth
- death
- emigration
- immigration
- Growth
- age at maturity
- sex ratio
Birth and death rates
- balance of additions and losses determine growth rate
- Inherent to all population growth models
When there is NO emi/ immigration, the population in ‘closed’
Nt = # of indiv. in pop. at time ‘t’
Nt + 1 = Nt + (births - deaths)
Exponential growth
Geometic:
- Populations grow faster as they grow bigger
Discrete:
- Population = periodically
Continuous:
- Reproduction = year-round
Resource limited growth
- Pop. growth is often resource limited
- Numbers cannot increase beyond the carrying capacity ‘k’
- Log curve graph, plateau at point when ‘k’ is reached
Estimating birth rates
- Count new-born individually
(monitor active bird nests)
Estimating death rates
- Difficult
Common methods:
Tagging
- Following indivs
- Possibility based
Population growth in ‘open’ systems
Nt + 1 = Nt + (birth-deaths) + (immigrants - emigrants)
Estimating demographic rates - Migrants
Tracnking movement
Tagging:
- Physical
- GPS
- Radio telemetry
- Acoustic
Population genetics
Estimating population size method
Mark-Release- Recapture (MRR)
- Estimates total population from sample proportion of recatures of mobile species.
Assumtions often hard to satisfy
- Closed population
- All organisms are equally able to be caught again
- tags not lost
Mark-Release- Recapture (MRR) equaiton
M/T = r/n
M = Number Marked
T = est. pop. size
r = recaptures
n = number caught on second attempt
Spacially structured populations
Metapopulations:
- Local population but individuals move
- Demographic rates vary spacially
- Large-scaled dynamics depends on local demographics and connectivity
Estimating growth and age
trees = rings
mammals = teeth
Fish = otoliths
Understanding age and size-structured population dynamics
Age and/ or size of individuals affects:
- Fecundity
- Survival
Population viability analysis (PVA)
- Tool to model dynamics over time
Uses:
- pop size/ carrying capacity
- Fecundity
- Mortality
- Inter-annual variations in parameters
Extinctions
Processes of chance that contributes to an extinction event:
- Catastrophes
- Human impacts
Stochasticity:
- Genetics
- Demographic
- Environmental
