Landscape-level Conservation Flashcards
What is a good population size to ensure long-term persistence of a species?
Minimal Viable Population
Define Minimal Viable Population (MPV)
VP for any given species in any given habitat is the smallest isolated population having a 99% chance of remaining extant for 1000 years despite the foreseeable effects of demographic, environmental, and genetic stochasticity*, and natural catastrophes
What does a Minimal Viable Population (MVP) do?
- Gives a quantitative estimate of population size needed to insure long-term survival.
-Estimate must plan for both normal and harsh years by assessing potential impact of stochastic events.
Define Minimum Dynamic Area (MDA)
Area of suitable habitat necessary for maintaining MVP
- Estimated by studying home-range sizes
What are potential consequences of
going below the MVP?
- Loss of genetic variability
- Demographic fluctuations
- Environmental fluctuations and natural catastrophes
Define genetic diversity
Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within species and can be attributed to the span of survival for a species
What is polymorphism
forms of the same gene
- the idea that an entity in code such as a variable, function or object can have more than one form
Define heterozygosity
The presence of two different alleles at a particular gene locus
- genetic variability!
Does the loss of genetic variability occur in small or large populations?
Loss of genetic variability (heterozygosity) occurs faster in smaller populations
Why do small populations have a faster loss of genetic variability?
Genetic drift
Define genetic drift
allele frequencies within a population change from one generation to the next based on random processes (depending on which individuals survive to maturity, mate, and leave offspring)
The math of Genetic Drift notes.
E.g. = rare allele (5% of alleles in gene pool) in population of 1000 vs 10 individuals
1000 individuals X 2 copies per individual X 0.05 allele freq. = 100 copies
10 individuals X 2 copies per individual X 0.05 allele freq. = 1 copy
The passing of alleles to future generations depends on what?
reproduction
Define Effective Population Size ( Ne)
size of the theoretical population that loses heterozygosity at a rate equal to the rate observed in the real population
= size of the population as estimated by the number of its breeding individuals.
What does Define Effective Population Size assume?
- assumes constant number of individuals in population
- assumes equal number of males vs females
What does a small (Ne) mean?
- With a small Ne the remaining genetic
variance decreases in each new
generation. - As Ne gets even smaller
the amount of genetic variance
decreases more rapidly between
generations.
List factors that can alter the effective populations size and thus, affect the rate of loss of heterozygosity.
A) Unequal Sex Ratio
B) Variation in Reproductive Output
C) Population Fluctuations and Bottlenecks
Define or list an example of unequal sex ratio
- Monogamous species (e.g. Scarlet macaws)
- Social systems (e.g. Northern Jacanas)
Define or list an example of Variation in Reproductive Output
e.g. Many plants)
- Many individuals produce 1,000,000’s of seeds whereas other individuals will produce 100’s.
- Results in some individuals being disproportionately represented in the next generation
Define or list an example of Population Fluctuations and bottlenecks
(e.g. butterflies, amphibians)
-Many species have populations that vary drastically from year to year.
- Ne is then a harmonic mean calculated for a given timeframe
- strongly determined by years that have the smallest populations
Define bottleneck
when the population is severely reduced so that rare alleles in the population are lost if no individuals possessing those alleles survive and reproduce.
Define or list an example of bottlenecks
(e.g. Ngorongoro lions)
Most damaging when population remains low (<10 individuals) for several generations
What are the consequences of reduced variability?
- inbreeding depression
- loss of evolutionary flexibility
Define inbreeding depression
Offspring receive two identical copies of a defective allele from each of its parents.
Negative effects include higher offspring mortality, fewer offspring, offspring that are weak, sterile, or have low mating success.
Define loss of evolutionary flexibility
- The loss of rare alleles or the inability to form unique allele combinations reduces chances of adapting to new/changing environments.
-Small populations less likely to have genetic variation necessary to adapt to long-term environmental changes, thus are more likely to go extinct.
Define demographic fluctuations
Variation in population size due to random variation in reproductive and mortality rates
within a population (or demographic stochasticity)
- Some individuals die young, others old
-Some individuals don’t reproduce, other reproduce a lot
Smaller populations are at greater risk to extinctions due to what?
due to increased probabilities of low/no births, and/or many deaths in one year.
Explain environmental fluctuations and natural catastrophes
- Variation in the physical environment (such as rainfall, temperature, cloud immersion
frequency) can alter food sources, predators, parasites, etc. that can alter birth & death
rates. - Natural catastrophes occur at unpredictable intervals and can wipe out a portion or all
individuals in a population
Small populations are more susceptible to what?
- unequal sex ratios
- allee effect
Define allee effect
occurs when social conditions are not met to continue normal behaviors.
