Chapter 8: Population Ecology Endangered Southern Sea Otter Chapter 8: Population Ecology Laura Cunningham 3rd Hour

Objectives What are the major characteristics of populations? Organisms disperse in their environment in three general patterns of population distribution: clumping, uniform dispersion, and random dispersion. Populations increase through births and immigration and decrease through deaths and emigration. When a population exceeds its resource supplies, many of its members will die unless they can switch to new resources or move to an area with more resources.

Objectives 2) How do populations respond to changes in environmental conditions? If a population overshoots its carrying capacity, the group must switch to new resources or move to an area with more resources. Species can increase their carrying capacity by developing adaptive traits through natural selection that reduce environmental resistance to their population growth. Weather, climate, and other factors can increase or decrease carrying capacity.

Objectives How do species differ in their reproductive patterns? Asexual vs. sexual reproduction; some are opportunists (r-selected species), some are competitors (k-selected species). Reproductive patterns may give a species a temporary advantage, but the availability of a suitable habitat for individuals of a population in a particular area determines its ultimate population size.

Population Dynamics and Carrying Capacity Population Dynamics – how and why populations change in their distribution, numbers, age structure, and density in response to changes in environmental conditions. Population Density – the number of individuals in a population found in a particular area or volume. Age Structure – the proportions of individuals at various ages in a population.

Limits on Population Growth Biotic Potential – maximum rate at which the population of a given species can increase when there are no limits on its rate of growth. The intrinsic rate of increase (r) is the rate at which a population would grow if it had unlimited resources. Environmental Resistance – all factors that act to limit the growth of a population. Biotic Potential + Environmental Resistance = Carrying Capacity (The maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat.)

Exponential vs. Logistic Population Growth No Population can increase in size indefinitely. Exponential Growth: starts slowly but then accelerates as the population increases because the base size of the population is increasing. (J-Shaped Curve) - Occurs when resources are not limited and a population can grow at its intrinsic rate of increase, or biotic potential.

Exponential vs. Logistic Population Growth Exponential growth is converted to logistic growth, in which the growth rate decreases as the population becomes larger and faces environmental resistance. Logistic Growth: involves rapid exponential population growth followed by a steady decrease in population growth with time until the population size levels off. (S-Shaped Curve)

Reproductive Patterns Asexual Reproduction – offspring are exact genetic copies (clones) of a single parent. Common in species such as single-celled bacteria. Many plants and animals such as coral reproduce this way. Sexual Reproduction – mixes the genetic material of two individuals and produces offspring with combinations of genetic traits from each parent. Used by 97% of earth’s species.

Opportunists and Competitors Opportunists (R-Selected Species) - reproduce early in their lifespan and produce large numbers of usually small and short-lived offspring in a short period. They have a high capacity for population increase. Ex) Dandelions, Cockroaches, Bacteria, Rodents - They reproduce and disperse rapidly when conditions are favorable or when a disturbance opens up a new habitat for invasion.

Opportunists and Competitors Competitors (K-Selected Species) – produce a few, often fairly large offspring but invest a great deal of time and energy to ensure that most of those offspring reach reproductive age. Ex) Elephants, Humans, Saguaro Cactus - They do well in competitive conditions when their population is near the carrying capacity. Their populations typically follow a logistic growth curve.

Survivorship Curve Graph that shows the percentages of the members of a population surviving at different ages. Three general curve types: late loss, which live to an old age (elephants, humans); early loss, where most members die at a young age (annual plants, bony fish species); and constant loss, which die at all ages (songbirds).

“We cannot command nature except by obeying her.” Sir Francis Bacon