Conservation Biology Exam 4

How does an introduced species become an invasive species?

• Lack of predator or competitor in new location

• May find easily exploited food source

• Some already adapted to new habitat

Water Hyacinth (example of invasive species)

• Forms dense mats on water surface

• Spreads by fragmentation or seeds (feet of birds)

How is water hyacinth invasive?

• Displaces natives (plants, waterfowl, etc)

• Obstructs waterways

• Increases water losses (transpiration)

Management of water hyacinth

• Removal

• Chemical control

• Mechanical methods

• Biocontrol

Few examples of organisms that are being overexploited

• Orchids

• Parrots

• Tropical fish

• Butterflies

• Marine mollusks

Industrialized fishing methods

• Driftnets

• Longline fishing

• Trawling

• Bycatch

Drfitnets

Transparent, nylon nets that span large expanses of water to capture passing fish

Longline fishing

Extremely long lines w/ thousands of hooks

Trawling

Dragging immense nets through the water or on the ocean floor

Bycatch

The accidental capture of non-target animals; Lost gear keeps on killing

Current bushmeat trade in Africa (example of overexploitation)

Larger primates & some ungulates most affected

Current bushmeat trade in Africa (solution)

• Restricting sale & transport of bushmeat, firearms & ammunition

• Closing roads after logging

• Extending legal protection to key endangered species

• Alternative sources of protein

Maximum Sustainable Yield

The theoretical amount that can be harvested yearly & maintain population size

Synergism

Effect of 2+ factors combined is more than the addition of their single effects

Habitat loss + harvest (synergism)

Rapid population decline

Environmental stress + introduced species (synergism)

Rapid increase in introduced species

Pollution + disease (synergism)

Increased susceptibility to disease

Minimum Viable Population (MVP)

• The smallest isolated population having a 99% change of remaining extant for 1000 years despite the foreseeable effects of demographic, environmental, & genetic stochasticity, & natural catastrophes

• Population size needed for long-term survival; needs to be high enough to survive effects of catastrophes

Minimum Dynamic Area (MDA)

Area of suitable habitat needed to maintain Minimum Viable Population (MVP)

Small populations prone to decline & extinction due to

• Genetic problems

• Demographic fluctuations

• Environmental fluctuations

Gene

Structure containing our hereditary information

Allele

Different forms of a gene

Gene pool

All the genes & alleles in a population

Gene flow

Transfer of genetic material btwn populations

Hybrid vigor

Increased fitness in a highly heterozygous individual

• More flexibility to challenges

• Functioning alleles may mask nonfunctional or harmful alleles

Evolution

Change in the genetic composition of a population over time

Adaptation

A process of genetic change in a population, due to natural selection, whereby the population becomes better suited for some feature in its environment

Adaptive radiation

Evolutionary divergence of a lineage into a variety of adaptive forms

Natural selection

Differential survival & reproduction of organisms due to their hereditary characteristics

Genetic drift

Change in allele frequencies due to chance

Genetic variability

Important b/c allows populations to adapt to changing environment

Wright’s formula

Calculating change in heterozygosity due to genetic drift

• H = 1-1/[2Ne]

H

Proportion of original heterozygosity retained after each generation

dF = 1/N=2Ne

Expected drop in heterozygosity per generation

Ne

Effective population size

Ht

Proportion of heterozygosity remaining after t generations

What maintains genetic variability?

Mutation & immigration

Effective population size (Ne)

Number of actually breeding individuals in a population

• Only includes adults & those adults who breed

Factors affecting Ne (Genetic Variation)

1. Unequal sex ratio

2. Variation in reproductive output

3. Population fluctuations

Unequal sex ratio

Affected by the fact the fewer members of one sex have a disproportionate representation in the next generation’s gene pool

• Polygamous situation → Ne = [4(NmNf)]/(Nm+Nf)

As the disproportionality increases…

Ne decreases

Variation in reproductive output

• Individuals don’t have same reproductive output

• Greater variation in output = lower Ne

Population fluctuations

When a population size fluctuates greatly annually, Ne will be somewhere btwn high & low but disproportionately affected by low years

• 1/Ne = 1/t(1/N1+…1/Nt)

Genetic bottleneck

When a population is severely reduced (e.g. to a few individuals) such that many (rare) alleles are lost

Inbreeding depression

Having fewer offspring or offspring w/ lower fitness b/c of mating btwn close relatives

Explanation of small population that are genetically similar

1. Less ability of homozygotes to be adapted in different situations vs. a heterozygote

2. Ability of harmful homozygous recessive alleles to express vs. masking of harmful alleles in heterozygote

Outbreeding depression

Lower reproductive output & evolutionary fitness in matings btwn different populations of a species or btwn closely related species

Problems of Demographic Variation

• Population size

• Sex ratio

• Group size effects

Population size

The effect of individual reproductive output

Sex ratio

In a small population, any fluctuation from an even birth sex ratio will have major effects on the effective population size (Ne)

Group size effects

Allee effect = inability of a species’ social structure to function once a population of that species falls below a certain number of density of individuals

Environmental Stochasticity (Environmental Variation)

Environmental variation w/ its effects are on all members of the population

Environmental variation results in lower…

• Population sizes

• Growth rates

• Higher probability of extinction

Synergism - Extinction Vortices

Subject to loss of genetic diversity, demographic variation, & environmental variation leads to smaller population

Examples of diseases

• Chestnut Blight (fungus)

• White nose syndrome (fungus)

  • Fungus on snout irritates bat, wakes them up from hibernation and leads to loss of energy reserves causing starvation

Introduced disease of humans

• Giardia

• Lyme disease

• West Nile virus

• Bird flu

Why is the bullfrog an invasive species?

• Prey on native species

• Outcompete native species for food & habitat

Why is the Tree of Heaven an invasive species?

• Reproduce rapidly

• Allelopathic properties → inhibits the growth of other plants nearby