Population Biology BCOR 012 Chapter 53 February 25 and 27, 2009

Population Ecology Chapter 52 I. Characteristics of Populations A. Introduction B. Two important characteristics of populations are density and the spacing of individuals (= dispersion) C. Demography II. Life Histories A. Natural selection favors strategies that maximize and individual ’ s fitness. B. Reproductive strategies C. Trade-offs between reproduction and survival

Population ecology is concerned with: measuring changes in population size and composition identifying the ecological causes of such fluctuations

Study of populations in relation to the environment Influences of environment on population: Density Distribution (dispersion) Age structure Size Population Ecology

From Chapter 23: So what is a population? A population is a set of individuals of the same species that live close enough together to interbreed. in a particular geographic area.

Density – the number of individuals per unit area Aerial census of African water buffalo in the Serengeti

Dispersion – the spacing among individuals within the population boundaries

Factors which influence population density and dispersion? Ecological needs of species Structure of the environment Interactions between individuals

Demography Study of the vital statistics of populations and how they change over time ~ Birth and Death rates

Demography is the study of factors that affect the growth and decline of populations. Populations increase as a result of births and immigration; they decrease as a result of deaths and emigration. A life table follows fate of a cohort from birth to death

Idealized survivorship curves Type I Few offspring with good care (mammals) Death rate low until older ages Type II Intermediate (rodents, annual plants) Death rate constant Type III Many offspring with little care (marine invertebrates, long-lived plants) Initial death rate high, then low

Reproductive rate The other key demographic factor determining size changes in populations without immigration or emigration Reproductive table ~ age- specific reproduction rates (Birth Rates)

Population Ecology Chapter 52 I. Characteristics of Populations A. Introduction B. Two important characteristics of populations are density and the spacing of individuals (= dispersion) C. Demography II. Life Histories A. Natural selection favors strategies that maximize and individual ’ s fitness. B. Reproductive strategies C. Trade-offs between reproduction and survival

Life history - the set of traits related to reproduction, including frequency of reproduction, number of offspring, investment in parental care, etc.

Reproductive Strategies Semelparous reproduction (big-bang) – A life history strategy in which the organism reproduces but once and then dies. Iteroparous reproduction – repeated reproduction over the course of the life span Giant palm of Madagascar White tailed deer - an iteroparous species

survival production of viable offspring Fitness involves both individual survival and the production of viable offspring that will live to reproduce themselves. Q.Therefore, why not a life history strategy that involves early reproductive maturity, frequent reproduction, and many offspring per brood?

Survivorship vs. brood size in European kestrel Trade-offs between reproduction and survival:

Organisms whose young are subject to high mortality rates often produce large numbers of small offspring. In other species, fewer and larger offspring are produced. r-selection r-selection: short life span, high reproductive output, high juvenile mortality, limited parental investment K selection K selection: long life span, low reproductive output, low juv. mortality, high parental investment

Population Ecology Chapter 52 III. Population Growth A.Exponential Growth B.Logistical Growth IV. Population Limiting Factors A.Density dependence B.Population fluctuations C.Boom and bust cycles V. Human Population Growth A.Earth’s carrying capacity B.What can you do?

Population Growth Growth rate results from processes that add and remove individuals + Births − Deaths − Emigration + Immigration

∆N ∆ t r is the per capita growth rate, r = b - d, where b is the per capita birth rate and d is the per capita death rate Growth curve for a population growing exponentially N is the population size

Kingfish, Louisiana, had a population of 1,100 individuals. They had a birth rate of 12/100, a death rate of 8/100, and an emigration (individuals leaving the population) rate of 2/100. How many people were added to Kingfish's population in one year? What is r? r = (b+i) - (d+e) r = ( ) = 0.02 rN=(0.02)(1,100) = 22 good job!

Exponential growth: Populations introduced to new or unfilled habitat Populations rebounding after catastrophe Rebound of the whooping crane population

In the notation of differential calculus, population growth is given as: dN dt (Note: here d is being used to symbolize very small change. It does not refer to the per capita death rate!) The maximum value of r, achieved under ideal growth conditions, is called the intrinsic rate of increase. It is noted as r max N. rN =

As b decreases and/or d increases, r, the per capita growth rate, decreases.

The carrying capacity (K) of an environment is the maximum population size that the environment can sustain with no degradation of the habitat.

As the population size (N) approaches carrying capacity (K), the population growth rate approaches zero.

dN dt By multiplying the exponential rate of increase r max N by (K - N)/K, we reduce the actual growth rate of the population as N increases. The Logistical Growth Equation  K - N   K  = r max N

The logistic model of population growth produces a sigmoid (S-shaped) curve when N is plotted over time.

How well do actual populations fit the logistical model? This laboratory population of Paramecium grew according a logistical model. This laboratory population of Daphnia overshot carrying capacity. And this natural population of song sparrows fluctuated considerably in response to environ- mental stresses.

Population Ecology Chapter 52 III. Population Growth A.Exponential Growth B.Logistical Growth IV. Population Limiting Factors A.Density dependence B.Population fluctuations C.Boom and bust cycles V. Human Population Growth A.Earth’s carrying capacity B.What can you do?

Density-dependent factors limiting population growth Plants: light, nutrients, water Animals: food, water, nesting/breeding sites Increased predation Accumulation of waste in the environment Increased transmission of disease Stress

Density-dependent limits on population growth are examples of negative feedback, a primary mechanism of self-regulation whereby the product of a process slows or stops that process. A non-biological example: your home heating system! When your thermostat senses that room temperature has fallen, it signals the furnace to come on. The product of furnace activity, heat, accumulates until the desired temp. is reached. The thermostat, sensing the accumulating heat in the room, then signals the furnace to shut off.

So what is an example of a density independent factor? Floods, for example: factors that have nothing to do with the size of the population in question.

Fluctuation in a moose population on Isle Royale, Lake Superior

Ten-year population cycles in the snowshoe hare and lynx.

Population Ecology Chapter 52 III. Population Growth A.Exponential Growth B.Logistical Growth IV. Population Limiting Factors A.Density dependence B.Population fluctuations C.Boom and bust cycles V. Human Population Growth A.Earth’s carrying capacity B.What can you do?

The human population is growing exponentially Where is K???

Age-structure pyramids for the populations of Afghanistan, the United States, and Italy

In the United States, our ecological footprint is large.

So what can you do about it? Live sustainably Use resources wisely Eat more vegetable protein and less meat Support global family planning efforts Work for peace and justice