Chapter 10: Mating + Small Populations

evolutionary flexibility

the ability of a species or population to adapt to changes in their environment over time

what three things affect populations

genetic

demographic

environmental changes

four mechanisms of evolution

selection

gene flow

genetic drift

mutation

selection

includes natural and sexual selection

the process by which some genes do better than others, either in response to natural or artificial (human) pressures

in response the genetic makeup of a population will evolve in future generations

gene flow

the migration of genes from one population to the next

genetic drift

random changes in gene frequencies, and is extremely strong in small populations

mutation

rare but is the ultimate progenitor of all variation that selection, gene flow, and genetic drift further manipulate

gene _____ and ________ can balance the effects of ______ ______ by providing new genes.

Gene flow and mutation can balance the effects of genetic drift by providing new genes.

Inbreeding depression

the negative effects of breeding with close relatives

Outbreeding depression

the negative effects of breeding with distantly related individuals

2 outbreeding depression consequences

sterility

loss of adaptive gene complexes

• reduced adaptation to both native and new environments

Population bottlenecks

occur when a population is so small that rare alleles can be lost from a population via genetic drift, leading to declines in heterozygosity

Founder effects

a type of bottleneck in which a few individuals leave a population to establish a new one, producing obvious effects on heterozygosity and inbreeding depression.

ex.) A single couple helped found an Amish community in Lancaster County, Pennsylvania, in 1744, and subsequent inbreeding in this socially isolated culture led to an increase in the Ellis-Van Creveld syndrome among the ancestors of this original couple.

50/500 rule

Isolated populations need at least 50 and preferably 500 individuals to maintain genetic variation.

Lande’s 1995 research suggested populations need at least _______ individuals to reliably maintain genetic variation.

at least 5000 individuals to reliably maintain genetic variation.

All of these so-called rules or magic numbers assume all individuals have an

equal probability of mating

• males and females vary considerably in reproductive success (males varying more than females)

• differences in mating and social systems across species

• not all individuals are capable of breeding (young and old)

rescue effect

populations that receive immigrants translocated from other populations are taken off the brink of local extinction

ex.) Florida Panthers

demographic variation

the differences in the characteristics of a population (age, sex, etc.)

Extinction can result directly from demographic variation, or it can also occur indirectly.

Ex.) One direct effect of demographic variation is species with very low birth rates (elephants and whales) will be strongly affected because it takes these species longer to recover from declines.

Ex.) One indirect effect of demographic variation in small populations is unequal sex ratios.

Unlike demographic effects, _________ variation often affects all individuals in a population.

environmental variation

flood, drought, fire, and fluctuations in parasites, predators, and competitors

MVP

Minimum Viable Population

the minimum number of individuals necessary to ensure the long-term survival of a species

MDA

Minimum Dynamic Area

the area of suitable habitat necessary for maintaining the MVP

PVA

Population Viability Analysis

a risk assessment that uses mathematical and statistical methods to predict the probability that a population will go extinct at some point in the future.

including a variety of variables, such as genetic, demographic, and environmental variation; species distribution; abiotic and biotic interactions; behavior; and habitat status, among other things.  

The four mechanisms of evolution are selection, genetic drift, gene flow, and ______.

mutation

A major driver of the loss of genetic variation is

genetic drift

If H = 0.90, the theoretical remaining heterozygosity remaining after 10 generations would be:

0.349

The most important mechanism for balancing the effects of genetic drift is

gene flow

The negative effects of breeding with individuals that are more closely related than random is called ______ depression.

inbreeding

Mating between distantly related individuals, like subspecies, can result in: (3 things)

outbreeding depression

loss of adaptive gene complexes

sterility

One example of a species thought to have gone through a population bottleneck in the past is the

cheetah

The 50/500 rule suggests that you need 50 and preferably 500 individuals to maintain

genetic variation

If a population has five males and eight females, what is the effective population size?

12.3

Factors affecting the calculation of effective population size include (3 things)

OSR

Variance in RS

population fluctuations

Understanding between-population genetic variation can help us restore genetic diversity to depauperate populations, which is called the

rescue effect

Demography is the study of:

populations

Demographic variation can both directly and indirectly lead to extinction.

True

The passenger pigeon may have gone extinct in part because of

Allee effects

Environmental variation is different than demographic variation in that it can affect ____ individuals in a population.

all

Because of the combined effects of genetic, demographic, and environmental variation on small populations, such populations tend to decline in an extinction ________.

vortex

Population Viability Analysis allows one to predict:

the probability that a species will go extinct in the future