Population Ecology and the Distribution of Organisms

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These flashcards cover key ideas from the lecture notes on population ecology, climate and biomes, growth models, life history strategies, and population regulation mechanisms.

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40 Terms

1
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What four physical factors are the major components of climate that most influence terrestrial biomes?

Temperature, precipitation, sunlight, and wind.

2
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Why is sunlight intensity highest at the equator?

Because sunlight strikes the equatorial region most directly, delivering more heat and light per unit surface area.

3
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What global pattern is created by warm, wet air rising at the equator and descending dry air at 30° N and 30° S?

A circulation pattern that produces tropical rain forests near the equator and many of the world’s deserts around 30° latitude.

4
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How do large bodies of water moderate coastal climates?

Water’s high specific heat causes it to absorb heat in summer and release heat in winter, reducing temperature extremes on nearby land.

5
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What is a 'rain shadow' and how is it formed?

A dry region on a mountain’s leeward side, formed when moist air rises, cools, and drops precipitation on the windward side, leaving dry air to descend.

6
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Define ‘biome’.

A major life zone characterized by dominant vegetation type on land or by the physical environment in aquatic settings.

7
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What is an ecotone?

A transitional area where two adjacent biomes or ecosystems meet and integrate.

8
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What does a climograph plot?

The annual mean temperature versus annual mean precipitation of a region.

9
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Which terrestrial biome has high temperature, high, year-round rainfall, and the highest biodiversity?

Tropical rain forest.

10
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Which biome is characterized by scattered thorny trees, seasonal rainfall, and large grazing mammals such as zebras?

Savanna.

11
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Name two key plant adaptations for survival in deserts.

Water storage (succulence) and reduced leaf surface area (spines or small leaves).

12
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What vegetation and climatic traits define chaparral?

Evergreen shrubs and small trees, mild wet winters and hot dry summers, and fire-adapted species.

13
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Which biome features fertile soils, seasonal drought, and is often converted to farmland?

Temperate grassland (prairie or steppe).

14
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What type of forest has deciduous trees that drop leaves in winter and experiences four distinct seasons?

Temperate broadleaf forest.

15
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Which is Earth’s largest terrestrial biome, dominated by cone-bearing trees?

Northern coniferous forest (taiga).

16
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What is permafrost and in which biome is it common?

Permanently frozen subsoil, common in tundra.

17
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Differentiate the photic and aphotic zones in aquatic biomes.

The photic zone receives sufficient light for photosynthesis; the aphotic zone is deeper and receives little light.

18
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What is the benthic zone?

The bottom substrate of aquatic biomes, consisting of sediments and inhabited by benthos communities.

19
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Define ‘thermocline’.

A narrow layer of abrupt temperature change that separates warm upper water from cold deeper water in oceans or lakes.

20
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Contrast littoral and limnetic zones in lakes.

The littoral zone is shallow, near shore, and supports rooted plants; the limnetic zone is open water too deep for rooted vegetation.

21
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What is dispersal, and why is it important in species distributions?

The movement of individuals or gametes away from their origin; it determines whether species can colonize new, suitable habitats.

22
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Name three common patterns of dispersion within populations.

Clumped, uniform, and random.

23
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What social interaction often produces a uniform dispersion pattern?

Territoriality or aggressive interactions among individuals.

24
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What is a survivorship curve, and what are its three idealized types?

A plot of the proportion of a cohort still alive at each age; Type I (low early death), Type II (constant death rate), Type III (high early death).

25
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What mathematical model describes unlimited population increase under ideal conditions?

The exponential growth model (dN/dt = rN).

26
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Define carrying capacity (K).

The maximum population size that a particular environment can sustain indefinitely.

27
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What term is given to the per-capita growth rate modified for limited resources in the logistic model?

(K – N) / K, which reduces growth as population size (N) approaches K.

28
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At what population size is growth rate highest in logistic growth?

At approximately K/2, when resources are still abundant but many individuals are reproducing.

29
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Explain r-selection versus K-selection.

r-selection favors traits that maximize reproduction in uncrowded environments; K-selection favors traits that enhance survival and competition at high densities near carrying capacity.

30
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Give an example of a density-independent factor affecting populations.

Weather events like drought or hurricanes that affect a population regardless of its density.

31
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List two density-dependent mechanisms that can regulate population size.

Competition for resources and increased disease transmission at high densities (others include predation, territoriality, accumulation of waste, intrinsic physiological factors).

32
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What is a life table?

An age-specific summary of the survival and reproductive rates of individuals in a population.

33
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How does a trade-off between offspring number and parental care influence life history strategies?

Limited resources force organisms to balance producing many small offspring with little care versus few large offspring with high parental investment.

34
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Define metapopulation.

A group of spatially separated local populations linked by immigration and emigration.

35
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Why might a population overshoot its carrying capacity before stabilizing?

Reproductive delay and resource depletion can cause population size to exceed resource availability before feedback reduces growth.

36
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What is territoriality and how can it be density dependent?

Defense of a physical space; as density rises, available territories decrease, limiting reproduction and increasing competition.

37
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Describe how disease acts as a density-dependent regulator.

Higher density facilitates faster pathogen transmission, increasing death rates as population size grows.

38
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What role do intrinsic physiological factors play in density dependence?

Stress or hormonal changes at high densities can reduce reproduction or survival even without external resource limits.

39
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How can life tables and survivorship curves be used in conservation biology?

They identify vulnerable life stages and forecast population trends, guiding efforts to protect endangered species.

40
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Why are oceans crucial to global climate and the biosphere?

They cover ~75% of Earth, regulate climate, drive rainfall through evaporation, and supply oxygen via marine photosynthesis.