Population

Ecology Organism Population Community Ecosystem Biome Biosphere Where Are We? Ecology is the study of organism interactions with each other and the enviornment.

Ecological processes occur at multiple levels of organization on Earth.

Each level of organization emerges from the processes of the level below it Big Questions: Make Sure You Can How Populations Grow Theory Reality Human Population Growth All members of a species in a contiguous area.

Populations are dynamic. Organisms enter a population in 2 ways:

Birth

Immigration

Organisms leave a population in 2 ways:

Death

Emmigration Model 1: Exponential Growth Model 2: Logistic Growth The growth of a population continues indefinitely.

Assumes no resource limitation.

Can be described by:

change in number of individuals (dN)

change in time (dt)

(r): the "per capita rate of increase", how many offspring per individual in the population As long as (r) is a positive value, a population will continue to increase at an exponential rate.

Higher (r) values will lead to faster rates of increase.

if (r) is 0, the population will not increase or decrease.

if (r) is negative, the population will decrease. The growth of a population decreases as the population approaches the "carrying capacity" (K) of the environment.

Models resource limitations.

The effect of (K) on (r) becomes greater as (N) approaches (K) How are real populations structured? How do real populations grow? How does evolution effect life history traits? How does the environment affect population growth? Measuring Population Size Population Distribution Population Demographics It can be difficult to estimate population size accurately.

"Mark-Recapture": 1 common method

Capture and mark members of the population.

Release them.

Recapture members of the population.

Number of marked individuals Recaptured marked individuals

=

Total population size Total recaptured individuals Individuals tend to be distributed in three major patterns: Clumped Uniform Random Demographics: The study of a population's vital statistics and how they change over time. Demographic Data can be arranged in tables (e.g. life tables, reproductive tables), or graphs (e.g. survivorship curves). There are 3 major types of survivorship curves demonstrated in real populations: Exponential Growth Typically occurs in small populations, well below the carrying capacity of the environment. Logistic Growth Much more common. Typically populations oscillate around the carrying capacity. Life History Traits: Any trait that affects an organism's life table.

Costs and benefits of all adaptations. Reproductive stategies Parental Care Semelparity: Produce a lot of offspring, once.

Iteroparity: Produce a few offspring, repeatedly Number of babies varies inversely with amount of parental care R-Selected vs. K-Selected Selection for traits that maximize reproductive success at low-population densities Selection for traits that maximize reproductive success at high population densities The effect of population density on population growth Density Dependent Population Regulation Competition Predation Territoriality Waste

Accumulation Intrinsic Factors Disease The underlying root of all anthropogenic ecological problems Historical Human Growth Rate The human population has been in a period of accelerated exponential growth since the industrial revolution...

...that growth rate is slowing The decrease in growth rate is not uniform accross the globe. As countries industrialize, various changes in demographics occur (the "demographic transition") It is, as of yet, unclear what the global carrying capacity for the human population is. How are populations structured?

How are populations affected by the environment? Explain how populations can be mathematically modeled.

Describe the relationships among all terms in population models.

Compare ideal populations to real-world populations.

Explain patterns of life-history, distribution, and survivorship.

Explain the costs and benefits of particular life-history characteristic adaptations and strategies.

Describe historical and current trends in the human population. A comparison of the exponential and logistic growth models for a population N = ~1,100 The Agave Plant: Semelparous Elephants (and all mammals): Iteroparous Data showing parental survivorship as a function of brood size in kestrels. "Age-Structure Pyramids" Human Population Growth change in number of individuals (dN) change in time (dt) per capita rate of increase

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# Ch.52: Population Ecology

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