Populations & Limits on Growth Ch. 5

APES Turn in: Salinity Lab Predator/Prey Lab Peppered Moth

Populations Group of similar individuals/species

Population Distribution Clumped (elephants) (b) Uniform (creosote bush) (c) Random (dandelions)

Why Clumping? Species tend to cluster where resources are available Groups have a better chance of finding resources Protects some animals from predators Packs allow some predators to get prey

How do populations change over time? Population Ecology  # of individuals of a species in an area AND how/why those # change over time Effected by: Resource competition Predation disease

Population Density # of individuals Area or volume Determined by external factors (habitat/resources) What is the population density of 200 birds in Population Density

Population Density What is the population density of 200 birds in 20 square miles? What about 200 birds in 5 square miles? Which area is more densely populated?

Limits on Population Growth Population Increase (+) Population Decrease (-) Births (b) Immigration (i) Death (d) Emmigration (e)

Growth Rate (r) (also termed rate of change) r = b - d If r (+), population size If r (-), population size If r (0), b=d, stationary population size

Therefore… True growth rate includes b, d, i, e r = (b-d)+(i-e)

How do populations change over time? Ideally, population would according to biotic potential

Biotic Potential Maximum rate at which a population can increase when there are no limits on its rate of growth

Biotic Potential is Influenced by: Reproduction age Reproductive periods # of offspring Care of offspring

GENERALLY… Organisms with a high biotic potential: Reproduce early in life Have short generation times Can reproduce many times Have many offspring each time they reproduce

GENERALLY… Small organisms have large biotic potential EX: Housefly – descendants = 5.6 trillion in 13 mo. Bacteria dividing in ½ every 30 min. Ancestors of Female housefly could be 5.6 trillion flies within 13 months – just a few years cover earth’s surface

Exponential Growth Results when organisms are growing at biotic potential Population size (N) Time (t) Exponential Growth

NO POPULATION CAN GROW INDEFINATELY!

Environmental Resistance All factors acting jointly to limit the growth of a population Population size determined by: Biotic potential Environmental resistance

Environmental Resistance Unfavorable environmental conditions due to resource availability As environmental conditions deteriorate, b and d

Carrying Capacity (K) Largest population that can be maintained given fixed resources - S (sigmoid) shaped curve (logistic Growth) Carrying capacity K Reflects influence of Env. Resistance Populations rarely stays at K If it rises above K, pop will crash Population size (N) Time (t)

What Happens When Populations Exceed Carrying Capacity Members of populations which exceed their resources will die unless they adapt or move to an area with more resources.

Population Cycles for the Snowshoe Hare and Canada Lynx Figure 5.18: This graph represents the population cycles for the snowshoe hare and the Canadian lynx. At one time, scientists believed these curves provided evidence that these predator and prey populations regulated one another. More recent research suggests that the periodic swings in the hare population are caused by a combination of top-down population control—through predation by lynx and other predators—and bottom-up population control, in which changes in the availability of the food supply for hares help to determine their population size, which in turn helps to determine the lynx population size. (Data from D. A. MacLulich) Fig. 5-18, p. 118

Minimum Viable Population (MVP) Estimate of smallest # of individuals necessary to ensure the survival of a population Red wolf – extinct 1980 Reintroduced in N.E. NC – Alligator river – genetically mixed with Coyote and gray wolf, but considered different species

Below MVP Extinction = Likely Individuals can’t find mates Genetically related individuals breed = weak or malformed offspring Genetic diversity = too low

Species Have Different Reproductive Patterns Asexual reproduction Sexual reproduction All species engage in struggle for genetic immortality by trying to have as many memberes of the next generation as possible carry their genes Costs/Risks/Benefits of sexual reproduction- see notes

Reproductive Strategies r-strategists k-strategists Life based on r (growth rate -r) Rapidly increase numbers Below carrying capacities for long periods of time Life based on carrying capacity (k) Live in a state of equilibrium Close to carrying capacity

Figure 9-9 Page 196 Reproductive Patterns K species; experience Carrying capacity K K species; experience K selection Reproductive Patterns Number of individuals r species; experience r selection Time

r strategists (based on study) + Live in disturbed environments. + Ecological generalists. + Have populations that fluctuate rapidly in size. + Do not compete well against other species + Are widely distributed. + Are slow to respond to ecological opportunities but live in wide varieties of environments. + Are short-lived. + Have many, relatively small young. + Have short periods of embryonic development. + Reach adulthood rapidly + Small sized adults. + Invest little or no parental care in young. + Reproduce once per lifetime. + Early successional species.

r-selected species Once established – population crash because Changing environment Invasion by more competitive species Go through regular BOOM and bust cycles

k strategists (based on study) + Live in stable environments. + Ecological specialists. + Have populations stable in size. + Compete well against other species. + Are restricted in distribution and where they can live. + Take rapid advantage of ecological opportunities but live in specific types of environments. + Are long-lived. + Have few, relatively large young. + Have long periods of embryonic development. + Reach adulthood slowly. + Large sized adults. + Invest intensive parental care in young. + Reproduce throughout lifetime + Late successional species.

K-selected species Do well when pop. size is near K Typically follow logistic growth Thrive in constant environment

Many organisms have reproductive patterns between the extremes of r & K, or change from one to the other depending on environment*

Percentage surviving (log scale) Survivorship Curves Percentage surviving (log scale) 100 10 1 Age

Reproductive strategy may give temporary advantage BUT the availability of suitable habitat determines ultimate population size

Factors Affecting Population Growth/Population Density Density Independent Limiting Factors Density Dependent Limiting Factors Floods Fires Hurricanes Unseasonable Weather Habitat Destruction Competition Predation Parasitism Disease

Zone of physiological stress Zone of physiological stress Range of Tolerance Lower limit of tolerance Higher limit of tolerance No organisms Few organisms Few organisms No organisms Abundance of organisms Population size Figure 5.13: This diagram illustrates the range of tolerance for a population of organisms, such as trout, to a physical environmental factor—in this case, water temperature. Range of tolerance restrictions prevent particular species from taking over an ecosystem by keeping their population size in check. Question: For humans, what is an example of a range of tolerance for a physical environmental factor? Zone of intolerance Zone of physiological stress Zone of physiological stress Zone of intolerance Optimum range Low Temperature High Fig. 5-13, p. 113