Chapter 52: Population Ecology 1.What is a population? -Individuals of a single species that occupy the same general area 2.What is the difference between density & dispersion? -Density – number of individuals per unit area or volume -Dispersion – pattern of spacing within the boundaries of population

Figure 52.2 Population dynamics Births and immigration add individuals to a population. Births Immigration PopuIation size Emigration Deaths Deaths and emigration remove individuals from a population. Factors that influence density….. Increase Decrease

Fig Patterns of dispersion within a population’s geographic range (b) Uniform. Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors. (a) Clumped. For many animals, such as these wolves, living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory. (c) Random. Dandelions grow from windblown seeds that land at random and later germinate.

Chapter 52: Population Ecology 1.What is a population? -Individuals of a single species that occupy the same general area 2.What is the difference between density & dispersion? -Density – number of individuals per unit area or volume -Dispersion – pattern of spacing within the boundaries of population 3.What factors influence population size? -Birth rate – fecundity -Death rate -Generation time -Sex ratio 4. What do the survivorship curves mean?

Figure 52.5 Idealized survivorship curves: Types I, II, and III I II III ,000 Percentage of maximum life span Number of survivors (log scale) Type I – most born survive & live to their maximum life span – us – k-selected Type II – constant death rate – each day has an equal opportunity for life or death Type III – high early death rate but survivors live to maximum life span – r-selected

Chapter 52: Population Ecology 1.What is a population? 2.What is the difference between density & dispersion? 3.What factors influence population size? 4.What do the survivorship curves mean? 5.What are the 2 main populations growth curves? - Exponential – “J”-curve

Figure 52.9 Population growth predicted by the exponential model ,000 1,500 2,000 Number of generations Population size (N) dN dt  1.0N dN dt  0.5N dN = Δ population size dt = Δ time r max = Births – deaths (intrinsic rate of increase) N = population size Species whose population size is primarily determined by birth rate = r-selected species

Self-Quiz A uniform dispersion pattern for a population may indicate that –A. the population is spreading out and increasing its range. –B. resources are heterogeneously distributed. –C. individuals of the population are competing for some resource, such as water and minerals for plants or nesting sites for animals. –D. there is an absence of strong attractions or repulsions among individuals.

Self-Quiz I would expect the potential for social interactions among individuals to be maximized when individuals –A. are randomly distributed in their environment. –B. are uniformly distributed in their environment. –C. have a clumped distribution in their environment. –D. are non-randomly distributed in their environment.

Self-Quiz Humans are an example of an organism with a type I survivorship curve. This means –A. mortality rates are highest for younger individuals. –B. mortality rates are highest for older individuals. –C. mortality rates are constant over the life span of individuals. –D. the population growth rate is high.

Ticket Out the Door

Chapter 52: Population Ecology 1.What is a population? 2.What is the difference between density & dispersion? 3.What factors influence population size? 4.What do the survivorship curves mean? 5.What are the 2 main populations growth curves? -Exponential -Logistic

Figure Population growth predicted by the logistic model dN dt  1.0N Exponential growth Logistic growth dN dt  1.0N 1,500  N 1,500 K  1, ,000 1,500 2,000 Number of generations Population size (N) K = carrying capacity Species whose population size is primarily determined by carrying capacity = k-selected species

Chapter 52: Population Ecology 1.What is a population? 2.What is the difference between density & dispersion? 3.What factors influence population size? 4.What do the survivorship curves mean? 5.What are the 2 main populations growth curves? 6.What is the difference between r-selected & k-selected species? r-selected (generalists)k-selected (equilibrial) Maturation time: shortlong Lifespan: shortlong Death ratehighlow Offspring/episode:manyfew Size of offspring/eggs:smalllarge Parental care:noneextensive Timing of 1 st reproduction:earlylate in life Reproductions/lifetime:usually 1several Examples:insects, fish, frogsmammals, birds 7. What factors limit a population?

Chapter 52: Population Ecology 1.What is a population? 2.What is the difference between density & dispersion? 3.What factors influence population size? 4.What do the survivorship curves mean? 5.What are the 2 main populations growth curves? 6.What is the difference between r-selected & k-selected species? 7. What factors limit a population? -Density – dependent factors – intensify as population size increases -Resource limitation -Health -Predation -Waste accumulation -Density – independent factors – effect population regardless of density -Weather -Climate -Environmental disasters

Figure Population cycles in the snowshoe hare and lynx Year Lynx population size (thousands) Hare population size (thousands) Lynx Snowshoe hare

Chapter 52: Population Ecology 1.What is a population? 2.What is the difference between density & dispersion? 3.What factors influence population size? 4.What do the survivorship curves mean? 5.What are the 2 main populations growth curves? 6.What is the difference between r-selected & k-selected species? 7.What factors limit a population? 8.How has the human population changed & how is it shown?

Figure Human population growth (data as of 2003) 8000 B.C B.C B.C B.C B.C A.D. 0 The Plague Human population (billions) 2000 A.D

Figure Age-structure pyramids for the human population of three countries (data as of 2003) Rapid growth Afghanistan Slow growth United States Decrease Italy Male Female Male FemaleMale Female Age Percent of population 80–84 85  75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 20–24 25–29 10–14 5–9 0–4 15–19 80–84 85  75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 20–24 25–29 10–14 5–9 0–4 15–19 Babies Group making babies Group NOT making babies Wide base = rapid growthSame width = slow growthNarrow base = decreasing

Self-Quiz A population’s carrying capacity is –A. the number of individuals in that population. –B. a constant that can be estimated for all populations. –C. inversely related to r. –D. The population size that can be supported by available resources for that species within the habitat.