Population Ecology Packet #80 Chapter #52

Introduction & Review Population Population Ecology Group consisting of members of the same species that live together in a prescribed area at the same time. Population Ecology The study of numbers of individuals of a particular species, at a given time and location, and the interactions of that population with other populations and the environment Population dynamics Study of changes in populations

Important Features of Populations Population Ecology Important Features of Populations

Population Density Population Density This is how population size is expressed The number of individuals of a species per unit space

Dispersion Dispersion Describes the spacing of individuals and there are three types.

Types of Dispersion Uniform Dispersion Clumped (Aggregated) Dispersion Individuals are evenly distributed Clumped (Aggregated) Dispersion Most common type Individuals are concentrated in specific parts of the habitat Patchiness Occurs as a result of distribution of resources or by asexual reproduction Random dispersion Occurs when individuals of a population are spaced throughout an area in a manner that is unrelated to the presence of others Least common; hardest to observe Results from a lack of interaction between individuals or a homogenous environment

Population Ecology Mathematical Models

Equation ∆N/∆t = b – d r = b – d ∆N is the change in numbers in the population ∆t is the change in time b is the natality (birth) rate d is the mortality rate r = b – d r is the growth rate of the population If r is 0, the population is stable If r > 1, the population is increasing in size If r < 1, the population is declining These equations can be expressed as dN/dt = rN N is the population size Represents arithmetic growth Population increases by the same amount over each interval of time Bubble Demonstration

Population Ecology Types of Growth Rates

Exponential Growth Exponential Growth Population growth is at a rapid pace Reflects the maximum intrinsic rate of growth Maximum rate of growth under ideal conditions for that population dN/dt = rmaxN rmax represents the maximum growth rate This type of growth may exist for a period of time until limiting factors become important Humans have exhibited this growth pattern for centuries—but can it last?

Exponential Growth & The Human Population I Thomas Malthus recognized that the human population cannot continue in exponential growth There has been a large decrease in death rate and the population continues to increase to unknown proportions No one knows the carrying capacity of humans. Human growth rate will continue to increase until humans hit carrying capacity Not all countries have the same growth rate Growth rate is higher in developing countries Africa and Southeast Asia countries Doubling time is the time needed for a population to double in size Replacement-level fertility is the number of children a couple must have to replace themselves 2.1 developed countries; 2.7 developing countries Total fertility rate Average number of children born to a woman during her lifetime Age structure of country can be used to predict future population growth Broader base shows growing population Narrower base shows shrinking population Environmental degradation is related to population growth and resource consumption Developed countries require more resources per capita Cause more environmental problems People overpopulation, too many people living in certain areas result in people over-utilizing resources

Exponential Growth & The Human Population II Not all countries have the same growth rate Higher in developing countries India South Asia Africa Age structure of a country can be used to predict future population growth Shows the percentages of population at different ages A broader base to the age structure indicates a growing population while a narrower base indicates a stable or shrinking population. Human growth rate will continue to increase until humans hit carrying capacity Not all countries have the same growth rate Growth rate is higher in developing countries Africa and Southeast Asia countries Doubling time is the time needed for a population to double in size Replacement-level fertility is the number of children a couple must have to replace themselves 2.1 developed countries; 2.7 developing countries Total fertility rate Average number of children born to a woman during her lifetime Age structure of country can be used to predict future population growth Broader base shows growing population Narrower base shows shrinking population Environmental degradation is related to population growth and resource consumption Developed countries require more resources per capita Cause more environmental problems People overpopulation, too many people living in certain areas result in people over-utilizing resources

Logistic Growth Logistic Growth Exponential growth with environmental resistance (carry capacity of the environment = K) incorporated into the equation dN/dt = rmaxN((K – N) /K) N = population size K = carrying capacity Maximum number of organisms that the environment can sustain indefinitely. Exhibited by most natural populations.

Potential Examination Question Logistic Growth Populations do not always approach and stabilize at K, but may overshoot K, followed by a population crash. Why does this occur? Provide an example. What reproductive strategies would be advantageous at high population densities (At or close to K)? What reproductive strategies would be advantageous at low population densities? High ability to reproduce with few resources ability to compete well for limited resources ability to use resources very efficiently organisms showing this type of strategy are sometimes called "K-selected", or equilibrial most likely to be found in stable habitats where population size does not vary much once it has approached K. Low early sexual maturity short generation time increased fecundity organisms showing this type of strategy are sometimes called "r-selected", or opportunistic most likely to be found in unstable habitats where environmental fluctuations result in large die-offs, or in newly colonized habitats where resources are not a limiting factor

Factors Influencing Population Size Population Ecology Factors Influencing Population Size

Dispersal Dispersal Movement of individuals among populations Immigration Migration of individuals into the population Emigration Migration of individuals out of the population If incorporated into the growth rate mathematical equation r = (b – d) + (i – e)

Density Dependent Factors Regulate population size and is difficult to access in nature and are limiting factors that increase in intensity as population size increases

Density Dependent Factors II Predation Disease Increases when contact with toxic waste, produced by population itself, increases with population size. Competition Intraspecific Competition between members of the same species Interspecific Competition between members of different species

Density Independent Factors Limit population size and are factors that do not increase in intensity as the population size increases. Most density-independent factors have some relationship to population density. Many climatic factors are density-independent.

Density Independent Factors Climatic factors Sunlight Rainfall Temperature All have impacts no matter what the population size Climatic and seasonal factors, monsoon season for example, can severely decrease populations

Life “History” Traits of Populations Population Ecology Life “History” Traits of Populations

Introduction Life history traits, products of natural selection, are traits that affect an organism’s schedule of reproduction and survival. Birth  Reproduction  Death

Semelparous vs. Iteroparous Species Semelparous Species Expend their energy in a single, immense reproductive effort Pacific salmon Agave Iteroparous Species Exhibit repeated reproductive cycles Most vertebrates Most shrubs Most trees

r Strategists r strategists Have traits that contribute to a high population growth rate. High r Small size Large numbers of offspring May live in unpredictable habitats Weeds Pests Roaches

K Strategists K strategists Maximize the chance of surviving in an environment where the number of individuals (N) is near the carrying capacity (K) of the environment. Population size near K Larger body size Long life span Late reproduction and slow development Have fewer offspring May care for their young African elephants Humans

Survivorship Survivorship is related to r and k selection Type I Survivorship Typical of K-selected organisms High mortality rate later in life Type II Survivorship Characterized by constant mortality rate over time Birds and lizards Type III Survivorship r selected organisms. Characterized by high mortality rate early in life

Survivorship Curves

Review

Review Students are encouraged to place their own questions and charts on following slides.