Ch 9 - Pop Distribution + Abundance

What is a population?

A group of individuals of a single species inhabiting a specific area.

What does population distribution describe?

The size, shape, and location of the area a population occupies.

What is abundance?

The number of individuals in a population.

What is population density?

The number of individuals per unit area or volume.

What does the environment shape in ecology?

The geographic distribution of species.

Why are species distributions limited by the environment?

Because organisms can only compensate for environmental variation in a limited way.

Why does environmental compensation involve tradeoffs?

Because regulating body temperature, water content, and other conditions requires energy.

What is a niche?

A summary of the environmental factors that influence a species' growth, survival, and reproduction.

What is a fundamental niche?

The physical conditions under which an organism can live.

What is a realized niche?

The restricted conditions under which an organism actually lives because of interactions with other organisms.

Why is the realized niche usually smaller than the fundamental niche?

Because competitors, predators, pathogens, and other biotic interactions restrict where a species actually lives.

How can niche diversity support biodiversity?

More niche differences allow more species to coexist.

Why can similar species coexist in the same broad region?

Because they use different parts of the environment or different resources.

What factors can influence species distribution?

Resource availability, climate, disturbance, habitat, parasites, pathogens, competitors, and microclimate.

Can relationships between environmental factors and species distributions stay constant?

Yes, they can remain stable for thousands of years.

Can species distributions also change rapidly?

Yes, distributions can change quickly when conditions change.

What is microclimate?

Local climatic conditions that may differ from the broader regional climate.

According to the lecture, why is the textbook wording about large and small scale misleading?

Because scale is a cartographic term, not simply a synonym for local versus broad area.

What does scale mean in cartography?

The amount of reduction a mapped feature has compared with its real size on the ground.

What do large-scale maps show?

A smaller area with greater detail.

What do small-scale maps show?

A larger area with less detail.

What wording did the lecture suggest using instead of confusing scale terms?

Broad versus fine, or regional versus local.

At a local level, what are the three main distribution patterns?

Random, regular, and clumped.

What is a random distribution?

A pattern in which each individual has an equal probability of occurring anywhere in the area.

What kind of interactions are associated with random distributions?

Neutral interactions among individuals and with the environment.

What is a regular distribution?

A pattern in which individuals are more uniformly spaced than expected by chance.

What kind of interactions often produce regular distributions?

Repulsion, antagonistic interactions, or local depletion of resources.

What is a clumped distribution?

A pattern in which individuals occur in patches or groups separated by areas of lower abundance.

What kinds of processes often produce clumped distributions?

Attraction among individuals or attraction to a common resource.

Across broad regions, what pattern is most common within populations?

Clumped distribution.

Why are populations often clumped at broad regional scales?

Because suitable habitat and resources are patchy rather than evenly spread.

How were aggressive tropical bee colonies distributed?

Regularly distributed.

Why were aggressive tropical bee colonies regularly distributed?

Because colonies interacted aggressively and defended spacing.

How were less interactive stingless bees distributed?

Randomly or clumped.

What factors influenced the distribution of desert shrubs?

Topography, water redistribution, soil characteristics, parent material, groundwater, local microclimate, and competition.

How can topography influence plant distribution?

By affecting water movement, drainage, and local environmental conditions.

How can groundwater influence plant distribution?

It changes access to water in different locations.

How can local microclimate influence plant distribution?

It changes temperature, moisture, and other local conditions.

How can competition shape plant distribution?

It can limit where individuals establish and survive.

What was the lecture point about creosotebush root distribution?

It minimizes within-species competition.

How can creosotebushes reduce within-species competition?

By limiting overlap of root systems compared with what would be expected if roots spread circularly.

What is the rhizosphere?

The soil region around roots that is densely populated with organisms.

How do roots communicate with organisms in the rhizosphere?

Mostly through chemical signaling.

What are root exudates?

Primary and secondary plant metabolites released by roots.

How can root exudates affect other organisms?

They can attract, deter, or kill herbivores, nematodes, and microbes, and inhibit competing plants.

How can topographic gradients influence plant abundance?

Different species may be most abundant at high, middle, or low slope positions depending on moisture and other conditions.

At continental scales, what kind of distribution do bird populations often show?

Clumped distributions.

What is the relationship between organism size and population density?

Population density generally declines as organism size increases.

How does average population density change with increasing body size?

It decreases.

Why do larger organisms usually occur at lower population densities?

Because larger organisms generally require more resources and space per individual.

Do all groups fall exactly on the same size-density relationship?

No, different groups vary around the general trend.

How is rarity classified in the lecture?

By geographic range, habitat tolerance, and local population size.

What are the three rarity factors?

Geographic range, habitat tolerance, and local population size.

Which populations are least threatened by extinction?

Those with extensive ranges, broad habitat tolerances, and large local populations.

Why does restricted geographic range increase vulnerability?

Because threats can affect a large fraction of the total population at once.

Why does narrow habitat tolerance increase vulnerability?

Because the species can survive only under limited conditions.

Why do small local populations increase vulnerability?

Because they are more easily wiped out by chance events and local disturbances.

What additional modern factor did the lecture say is important for extinction risk?

Genetic diversity.

Why is genetic diversity important to persistence?

It improves the ability of populations to adapt and reduces problems associated with small populations.

What is one example of rarity type I?

Extensive range, broad habitat tolerance, but small local populations.

What is the peregrine falcon an example of?

A species with extensive range, broad habitat tolerance, and small local populations.

Why did peregrine falcons approach extinction?

Because DDT-contaminated prey caused severe declines.

How did tiger rarity increase despite a historically broad range?

Hunting reduced the range to tiny, fragmented populations.

What is one example of rarity type II?

Extensive range and large populations, but narrow habitat tolerance.

Why did the passenger pigeon go extinct despite huge numbers?

It depended on large virgin forests for nesting, and logging plus hunting caused extinction.

Why was the harelip sucker vulnerable even though it was broadly distributed?

Because it required a narrow habitat type: large pools with rocky bottoms in medium-sized streams.

How did habitat alteration contribute to harelip sucker extinction risk?

Silting of rivers eliminated its required habitat.

What is extreme rarity?

Restricted range, narrow habitat tolerance, and small populations.

Which kinds of species often show extreme rarity?

Many island species.

Why are many island species especially vulnerable to extinction?

Because they often have restricted ranges, narrow tolerances, and small populations.

What is the kakapo used as an example of?

Extreme rarity.

Why is the kakapo especially vulnerable?

It is rare, flightless, slow, ground-nesting, produces only a single egg, and evolved without mammalian predators.

Why is evolving without mammals a problem for the kakapo?

It is not easily frightened by predators it did not evolve with.

Why is ground nesting risky for the kakapo?

Ground nests are highly vulnerable to introduced predators.

How can low reproductive output increase extinction risk?

It slows recovery after population declines.

How do the study guide ideas of density, abundance, and distribution fit together?

Abundance is how many individuals there are, density is how crowded they are, and distribution is where they occur.

How do niche concepts connect to biodiversity?

Differences in niches allow species to partition environments and coexist, increasing biodiversity.

How do distribution patterns connect to rarity?

A species may be rare because it occurs in few places, tolerates few habitats, or has small local populations.