Environmental Science Final (Untested material)

Biological community

All of the populations living and interacting in a particular area.

Ecological Niche

Describes either the role played by a species in a biological community or the total set of environmental factors that determine a species distribution.

Generalist Species

has a broad niche (raccoon)

Specialist Species

has narrow niche (panda)

Realized Niche

the portion of the fundamental niche that is actually filled due to competition or other species interactions.

Fundamental Niche

when a species fulfills its entire role by using all the available resources.

competitive exclusion

no two species can occupy the same ecological niche at the same time. The one that is more efficient at using resources will exclude the other.

species coexistence

neither species fully excludes the other from resources, so both survive.

resource partitioning

species co-exist in a habitat by utilizing different parts of a single resource.

Coevolution between species

As predators become more efficient, prey evolve defenses. Predator and prey evolve in response to one another. (Ex: plants develop thorns to deter herbivores from eating them. Herbivore can then evolve to counter this evolution

Foundation species

form the physical basis or “structure” of an ecosystem, supporting many others (Coral reefs provide habitat and protection for thousands of marine species).

Keystone species

have a disproportionately large effect on their ecosystem; their loss can trigger a trophic cascade (Wolves in Yellowstone control elk populations, allowing vegetation and songbirds to recover).

Ecosystem engineers

modify physical habitats, changing resource availability for other species (Beavers build dams that create wetlands supporting fish, amphibians, and birds).

Size factor of population growth math

number of individuals in a population (N)

Density factor of population growth math

number of individuals per unit area

Rate time factor of population growth math

rate (r) the number of individuals which can be produced per unit of time (t)

How to calculate the rate of a population

r = (b + i) - (d + e)

Population growth rate = r = (birth rate + immigration rate) - (death + emigration rate)

Exponential Growth

growth at a constant rate of increase per unit time (geometric) ; has no limit. (dN/dt = rN). When a quantity increases at a rate proportional to its current size, meaning it grows faster and faster over time

Logistic Growth

Resource scarcity slows exponential growth. Slowing rate of growth results in an “s-shaped” or sigmoidal growth curve. Such growth is also sometimes referred to as logistic growth and can be represented mathematically as dN/dt = rN (1 − N/K).

R selected species

rely upon a high reproductive rate to overcome the high mortality of offspring with little or no parental care (for example: a clam can release a million eggs in a lifetime, with few surviving to maturity).

K selected species

have few offspring, slower growth as they near carrying capacity and exercise more parental care (for example: an elephant produces one offspring every 4 or 5 years, but nurturing by a herd increases the likelihood of it surviving to maturity).

Type I pattern of survivorship

full physiological life span if organisms survives childhood (elephants and bears)

Type II pattern of survivorship

Probability of death unrelated to age (gulls and mice)

Type III pattern of survivorship

TBD - mortality

Difference between human populations from populations of other organisms

Technology has allowed us to raise global carrying capacity (K) for humans repeatedly.

Malthusian population theory

Human populations increase exponentially but food supplies grow linearly. This is because humans reproduce rapidly when food and space are available. Only so much land and slow tech growth limit food production. Results in population eventually outpaces food leading to scarcity and competition. The human population will reach it’s carrying capacity because food is limited.

Criticisms of Malthusian population theory

• Humans have ability to raise carrying capacity

• Population rose rapidly in Western Europe but food supply kept pace.

• Industrial and agricultural revolutions boosted production through new tools and technology.

• Food output often outpaced population growth. (Ex: Only 2% of U.S. workers are in agriculture, yet GDP exceeds $14 trillion)

• Land wasn’t the limit Malthus imagined — global trade and efficiency expanded resources.

• Technology increased carrying capacity, challenging Malthus’s predictions.

Demographic transition theory

Model of economic and cultural change to explain declining death rates, declining birth rates, and rising life expectancies in nations as they become industrialized.

Four stages of demographic transition theory

• Pre-industrial stage - birth and death rates are high

• Transitional stage - death rates decrease, birth rates stay high

• Industrial stage - lower death rate is consistent, birth rates decrease

• Post-industrial stage - birth rates and death rates are low