Chapter 11 - Population Dynamics Flashcards
Represent changes in population size due to birth, death, immigration, and emigration as a mathematical equation
N(t+1)=N(t)+B+I-D-E
Where:
N(t) is the initial population
B is the birth rate
I is the immigration Rate
D is the death Rate
and E is the emigration rate
In population dynamics, these are sets of populations linked by dispersal
Metapopulations
In population dynamics, these are sets of populations that face the threat of extinction
Small populations
4 major types of patterns of population growth
Exponential growth
Logistic growth
Population fluctuations
Regular population cycles
T/F The growth types are mutually exclusive
F, a single population can experience these 4 major types of growth at different times; the 4 are not mutually exclusive
Growth pattern where population increases (or decreases) by a constant proportion at each point in time
Exponential Growth
Means by which species successfully colonize new geographic regions on their own
Long distance or Jump Dispersal events
Growth pattern with relatively stable population size that changes little with respect to time; at equilibrium.
Logistic growth
In natural populations, indicates any population whose numbers initially increase then level off and fluctuate around a maximum population size or carrying capacity (K)
Logistic Growth
dN/dt = rN(1-(N/K))
where:
N is the population count
r is the instantaneous rate of change
K is the population size at which birth and death rates are equal
Most common pattern which may be erratic increase or decrease in abundance from overall mean, or deviations from population growth patterns (i.e. exponential, logistic)
Population Fluctuations
Alternating periods of high and low abundance after constant or nearly constant time intervals
May be due to internal factors (hormonal or behavioral changes in response to crowding) and external factors (weather, food supplies, predators)
Regular Population Cycles
The effect of population density is often delayed with?
Time
Ex. Built-in delay in the effect of food supply on birth rate; current number of individuals born influenced by population densities or other conditions present several time periods ago
How to calculate population under delated density dependence
dN/dT = rN [1-(N(t-tau)/K)]
Where:
Tau is time lag
Similar to logistic growth equation, instead of N, we use N(t-tau) which is the size of the population in the past not current
Using the geometric growth equation, why are small populations at risk of extinction
N(t+1) = λN(t)
If fluctuation very little → λ mostly greater than 1 in most years → population generally increase in size → little to no risk of extinction
If change in λ is large from year to year → population size fluctuates → Additional variation in λ slows population growth → increased extinction risk
In small populations, when genetic drift leads to loss of genetic variation, why is this harmful
1.) a small population cannot respond via natural selection optimally
2.) harmful alleles occur at higher frequencies leading to poor reproductive success,
3.) small populations have more occurrences of inbreeding -> increases frequency of homozygotes -> increases frequency of a harmful allele
Chance event types that threaten small populations to extinction
genetic, demographic, and environmental events
Chance events related to the survival and reproduction of individuals
Demographic Stochasticity (ex. kidlatan ka bigla ni god)
Why are small populations threatened by demographic stochasticity?
When population size is large, there is little risk of extinction from demographic stochasticity because of laws of probability
When the population growth rate (r or lambda) DECREASES as the population density decreases because individuals have difficulty in finding mates at low population densities
Allee effects
Erratic or unpredictable changes in the
environment; refers to changes in the average birth rate or death rate in a population from year to year because environmental conditions vary over time.
Environmental Stochasticity
Can eliminate or drastically reduce the size of populations, even those that seem large enough to be at little risk of extinction
Natural catastrophes
Spatially isolated populations that affect one another’s dynamics because individuals (or gametes) occasionally disperse from one population to another
Metapopulations
Characterized by repeated extinctions and colonization
Metapopulations
Populations of some species are prone to extinction for two reasons:
Patchiness of their habitat makes dispersal between populations difficult
Environmental conditions can change in a rapid and unpredictable manner
According to Richard Levins, represent metapopulation dynamics in terms of the extinction and colonization of habitat patches
dp/dt = cp(1-p)-ep
where:
p = proportion of habitat patches that are occupied at time t
c = patch colonization rate
e = patch extinction rate
Assumptions of Richard Levin’s equation
- There is a very large (infinite) number of identical habitat patches
- All patches have equal chance of receiving colonists (hence spatial arrangement of patches does not matter)
- All patches have an equal chance of extinction
- Once a patch is colonized, its population increases to its carrying capacity much more rapidly than the rates at which extinction and colonization occur (this assumption allows population dynamics within patches to be ignored)
T/F For a metapopulation to persist for a long time, e/c ratio must be less than 1
True
T/F Extinction rate is less than colonization rate when e/c > 1
False, greater than
T/F A metapopulation can go extinct even when suitable habitat remains
True
When human actions convert large tracts of habitat into sets of spatially isolated habitat fragments
May cause a metapopulation’s colonization rate ( c ) to decrease because patches become more isolated and harder to reach by dispersal
Habitat Fragmentation
T/F Extinction and colonization rates rarely vary among patches
False, often vary
Tendency for high rates of immigration to protect a population from extinction by reducing the problems associated with small population size
Rescue effect
When abundance of a population is limited by nutrient supply or food
availability
Bottom-up control
hen abundance of a population is limited by predators
Top-down control
