midterm.htm

Name: ________Key_______________

NRE 220 Midterm - Winter 1998

Multiple choice. (3 points each; Total 30)

1) What are the 4 components of the "evil quartet" as causes of extinction?

(a) Inbreeding, domino effects, habitat loss, overhunting

(b) Poaching, non-native species, edge effects, climate change

(d) Habitat loss, domino effects, pollution, predation

2) What is an endemic species?

(a) A species which is on the brink of extinction.

(b) A species which is only found in a single geographical area.

(d) An introduced species which is driving other species to extinction.

3) What two major arguments have been presented, either alone or in combination, as explanations for the Pleistocene mass extinction?

(a) Climate change; overhunting

(b) Meteor impact; volcanic activity

(d) K-T boundary effect; global cooling

4) What three major groups of organisms contain the largest number of known species?

(a) Vertebrates, flowering plants, and insects

(b) Flowering plants, insects, and other arthropods

(d) Insects, fungi, and protists

5) The "50/500" rule is based upon:

(a) Inbreeding and demographic stochasticity

(b) Inbreeding and genetic drift

(d) Evolutionary potential and intrinsic growth rate "r"

6) Genetic heterozygosity is most likely to be retained in:

(a) Small populations over many generations

(b) Large populations over many generations

(d) Large populations over few generations

7) The Heath Hen was driven to endangerment and then extinction by

(a) Overhunting

(b) Environmental variability

(d) Disease

(e) Two of the above

(f) All of the above

Name: ________Key_______________

8) If the annual growth rate ( , lambda) for a given species of concern = 0.85, what trend will we see in population numbers?

(a) Population will increase

(b) Population will decrease

(d) Population will stay the same

9) Effective population size

(a) Typically is equal to or greater than N

(b) Is an estimate of the number of females in the population

(d) Is likely to be high in species that exhibit male dominance behavior

10) Which of the following organisms best fits the following pattern?

(a) marine fish

(b) humans log (probability of

(d) song sparrow

Age

Short answer. (Points as indicated; total 70)

11) Explain what is meant by the Hardy-Weinberg equilibrium, and list its assumptions. (5 points)

2 The Hardy-Weinberg equilibrium model states that allele (gene) frequencies remain constant from generation to generation, given the following assumptions:

3 Large population size

No mutation

No migration

Random mating

No natural selection

12) Explain the keystone species concept and support your response with an example. (5 points)

3 A keystone species is a member of a biological community which may be critical in determining the ability of other species to persist in the community. The removal of a keystone species may result in the loss of numerous other species. Alternatively, keystone species may help to control the populations of other species in the community.

2 Examples: Starfish (pisaster) in rocky intertidal is a keystone species for 14 other species (barnacles, limpets, chitons, snail, macroalgae). Removal of the starfish results in a collapse of the system to only 9 species.

Kangaroo rat - When K-rat is excluded from part of the community, plants with large seeds thrive, whereas those plants are limited by K-rats in open range.

Other examples include the sea otter, gray wolf, and fig trees.

Name: ________Key_______________

13) In attempting to conserve biological diversity, we may wish to conserve as many species as we can, or we may wish to conserve as many higher-level (e.g. family) groups as we can. Describe this distinction and briefly explain the benefits of each approach. (5 points)

Conserving as many species as possible literally means saving the "tips" of the tree of life, while conserving as many families, or higher taxonomic groups, means saving at least parts of "branches" of the tree of life.

It is easier to identify and protect individual species - they are the fundamental unit of classification, they are used to define laws, and they are good indicators of habitat quality.

Higher taxonomic units represent the major diversity of life if one thinks in terms of large, morphologically distinct groups. If we try to conserve as many families as possible, some species extinctions might be considered acceptable as long as part of the branch is retained. This might make conservation easier by balancing extinction of some species with protection of other members of the same family.

14) What is a domino effect? Provide an example. Name the major species involved (at least two) and briefly explain why this should be called a domino effect. (5 points)

3 A domino effect occurs when the rarity or extinction of one species causes the rarity or extinction of one or more other species.

2 Examples:

Dodo and Calvaria tree on Mauritius. The tree's seeds had to pass through the gut of the dodo in order to germinate. When the dodo was hunted to extinction, the trees stopped reproducing and now only very old individuals remain.

Prairie dog and black-footed ferret. The ferret is a specialized hunter of prairie dogs and lives in abandoned prairie dog dens. When prairie dogs were eradicated by farmers settling the plains, the ferret was nearly driven to extinction and is now one of the most endangered species in the US.

15) The species-area relationship was first described for islands. Sketch the relationship, label the axes, and briefly explain the graph in words. (5 points)

3 loge (# of species)

log (# of species)

loge (area) or log (area)

2 Each point represents an island. Larger islands contain more species than smaller islands. The relationship is log-linear.

Name: ________Key_______________

16) Invasive species. (10 points)

(a) List three characteristics of successful invasive species. (3 points)

1 High reproductive rate Vegetative or clonal reproduction

each Pioneer species High genetic variability

Short generation time Phenotypically plastic

Long-lived Broad native range

High dispersal rate Habitat generalist

Single-parent reproduction Broad diet (polyphagous)

Human commensal

(b) List three characteristics of invadable communities. (3 points)

1 Climate matches that of original habitat of invader

each Early successional

Low diversity of native species

Absence of predators of invading species

Absence of native species morphologically similar to invader

Absence of predators or grazers in evolutionary history ("naive" prey)

Absence of fire in evolutionary history

Low-connectance food web

Anthropogenically disturbed

(c) Provide an example of an invasive species. Briefly describe its impact on the ecosystem and why it is so successful. (4 points)

1 Examples include zebra mussel, spiny water flea, sea lamprey, purple loosestrife, Nile perch, gypsy moth, feral pigs, introduced goats and rabbits.

3 Explain why and how the species is impacting the ecosystem (typically competition - e.g. purple loosestrife, spiny water flea - and predation - e.g. sea lamprey, Nile perch. Grazing, spread of disease, and hybridization are other mechanisms; positive effects may also be indicated - e.g. honey bee, crops). Include whether the species is threatening native species - e.g. Nile perch, loosestrife.

17) What is a metapopulation? Using this concept, explain how habitat fragmentation potentially puts species at risk of extinction. (6 points)

2 A metapopulation refers to a number of spatially distinct subpopulations which may experience some exchange of individuals.

2 Habitat fragmentation creates small subpopulations because each habitat fragment can only support a small number of individuals.

2 Unless there is enough dispersal for subpopulations to be recolonized, each will eventually go extinct due to demographic and genetic risks.

Name: ________Key_______________

18) Species diversity. (9 points)

(a) Explain the concept of a latitudinal gradient in terms of biological diversity. (3 points)

As one proceeds from high (polar) latitudes to low (equatorial or tropical) latitudes, the number of species increases dramatically.

(b) Four possible explanations for the existence of these gradients were discussed in class. Briefly describe two of them. (6 points)

3 points for each explanation.

(1) High primary production in the tropics resulting from high and constant year-round solar energy input results in larger numbers of individuals, hence an opportunity to divide resources among a larger number of species.

(2) Species interactions including competition, predation, and mutualism are more intense in the tropics, potentially raising species richness. These interactions can lead to greater specialization, hence smaller niches and more species. Predation can also prevent a dominant competitor from eliminating less effective competitors, hence favoring coexistence of more species.

(3) Greater environmental stability in the tropics allows greater specialization because the environment is more constant and predictable, and organisms don't have to invest so heavily in adaptations to extreme or varying environmental conditions.

(4) Environmental constancy: A longer time span without disturbance (such as multiple advances and retreats of glaciers) permits more evolutionary specialization and speciation to occur. (Although some evidence indicates that frequent disturbance can actually increase speciation rates.)

19) Population growth. (6 points)

(a) Draw a diagram of density-dependent growth. Include axes labels. (3 points)

K = carrying capacity

(population

size)

t (time)

r = the intrinsic rate of natural increase or per capita growth rate

K = the carrying capacity of environmentally-imposed upper limit on growth

N = the population size at time t

Name: ________Key_______________

20) Risks of rarity. (14 points)

(a) A species that has been made rare by human activity may recover, or it may go extinct. List and explain the main categories of risk that are thought to be responsible for rare species becoming extinct. (10 points)

2 points each for identifying and describing the two major categories, one point for each subcategory, 1 extra point for completeness of explanation.

Demographic risks: Random variations in biological communities and in the natural environment that can cause variation in the population size of a species. Chance fluctuations may lead to extinction. Demographic risks include:

- demographic stochasticity (chance variation in birth and death rates or sex ratio)

- environmental variation (year to year fluctuations which can cause variation among individuals in a population or across multiple populations, e.g. excessive rainfall or drought)

- catastrophes (episodic extreme events such as fires or hurricanes which can threaten entire populations)

Genetic risks: Loss of genetic variation resulting in greater chance of extinction.

- inbreeding (mating between close relatives - most likely in small populations, resulting in alleles being identical by common descent; can lead to expression of harmful alleles, i.e. homozygous recessive traits)

- genetic drift (chance loss of genetic variation which can result in a greater tendency to go extinct if a new disease, new predator, or some other change occurs in the environment)

(b) Contrast the relative vulnerability of large-bodied vs. small-bodied species to the types of risk described in part (a). (4 points)

2 Large-bodied species are slow reproducing but long-lived. They are vulnerable to recurrent catastrophes, but their long life spans make them less vulnerable to demographic stochasticity. They also experience drift at a slower "real time."

2 Small-bodied species have short lifespans and high rate of growth (reproduction). They can recover quickly from recurrent catastrophes, but can be wiped out by demographic accidents due to their short lifespans.