Chapter Fitty-Two Population Ecology Chuck and Metzler and Baldwin’s Little Sister

WHAT IS POPULATION ECOLOGY? POPULATION ECOLOGY IS THE STUDY OF POPULATIONS IN RELATION TO THE ENVIROMENT INCLUDES ENVIROMENTAL INFLUENCES ON POPULATION DENSITY AND DISTRIBUTION, AGE STRUCTURE, AND VARIATION IN POPULATION SIZE

density and dispersion density- the number of individuals per unit area or volume dispersion- the pattern of spacing among individuals within the boundaries of the population

FACTORS AFFECTING DENSITY AND DISPERSION IMMIGRATION-INFLUX OF NEW INDIVIUALS FROM NEW AREAS EMIGRATION– MOVEMENT OF INDIVIUALS OUT OF A POPULATION BIRTH AND DEATH RATES ECOLOGICAL NEEDS OF SPECIES STRUCTURE OF THE ENVIRONMENT

patterns of dispersion clumped- most common pattern, indicates heterogeneous environment related to social interaction between individuals uniform- related to competition for resources and result from interaction between individuals, can result from territoriality random- not common, indicates the absence of strong interaction between individuals or a fairly consistent habitat

DEMOGRAPHY DEMOGRAPHY- THE STUDY OF THE VITAL STATISTICS OF POPULATIONS AND HOW THEY CHANGE OVER TIME CAN BE SUMMARIZED USING A LIFE TABLE A LIFE TABLE PRESENTS AGE SPECIFIC SURVIVAL DATA FOR A POPULATION A SURVIVORSHIP CURVE SHOWS THE NUMBER OR PORPORTION OF MEMBERS OF A GROUP OF INDIVIDUALS STILL ALIVE AT EACH AGE – THREE TYPES OF SURVIVIORHSIP CURVES TYPE I- LOW MORTALITYDURING EARLY AND MIDDLE AGE AND A RAPID INCREASE WITH OLD AGE TYPE II- DEATH RATE IS RELATIVELY CONSTANT THROUGHOUT THE LIFE SPAN TYPE III- TYPICAL OF POPULATIONS THAT PRODUCE MANY OFFSPRING, MOST OF WHICH DIE OFF RAPIDLY. FEW SURVIVE TO REACH ADULTHOOD. REPRRODUCTIVE TABLE- A FERTILITY SCHEDULE THAT IS AN AGE SPECIFIC SUMMARY OF THE REPRODUCTIVE RATES IN A POPULATION

Life History Life History- the history of an organism from birth through reproduction to death, and reflects evolutionary trade-offs between survival and reproduction Includes age at first reproduction, how often an organism breeds, and the number of offspring produced during each reproductive “episode” Two Types of Life History – Big Bang Reproduction (semelparity)- “one shot” pattern – single reproductive “opportunity” – Repeated Reproduction (iteroparity) – repeats the reproductive “act” annually for several years

Exponential Model The Exponential Model describes population growth in a idealized, unlimited environment. Two Types of Exponential Models – Type I Per Capita Birth Rate (b) & Per Capita Death Rate (m) can be expressed in terms of the average number of births and deaths per individual during a time period r = b – m, where r equals per capita rate of increase Zero Population Growth occurs when r = 0 – Type II Exponential Population Growth occurs when the intrinsic rate of increase (r max ) is the fastest Per Capita rate of increase possible for a species dN/dt = r max N where N equals population size Produces a J-shaped growth curve

Logistic Growth Model Carrying capacity(K)- the maximum sustainable population size that a particular environment can support at a particular time. Logistic population growth- reflects the impact of the increasing N on the per capita rate of increase as the population approaches the carrying capacity. This model produces an s-shaped growth curve. The logistic model makes the assumption that any increase in population numbers will have a negative effect on population growth. Allee Efect- when individuals benefit as the population grows. K-selection – populations at high density close to carrying capacity may experience this density dependent selection for traits such as competitive ability and resource utilization. r-selection – density independent selection which favors traits that maximize population growth such as production of numerous,small offspring.

Density Independent VS Density Dependent Density independent- when the birth rate or death rate does not change as population density changes. Density dependent- when death rate rises and birth rate falls with increasing population density. - An example of negative feedback. Equilibrium density- when birth rate or death rate or both are density dependent.

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Reasons for Change in Population Competition for Resources Territoriality Health Predation Toxic Waste Intrinsic(Physiological) Factors

Population Dynamics Population Dynamics studies these variations in population size and the factors that cause them. Metapopulation- a group of populations in which immigration and emigration may significantly influence individual population sizes.

Human Population Human Population growth has slowed after centuries of exponential increase. The transition from zero population growth equals(=) high birth rate minus (-) high death rate TO zero population growth equals (=) low birth rate minus (-) low death rate is called the demographic transition. Age Structure influences present and future growth. Infant mortality- the number of infant death per one thousand live births Life Expectancy at Birth- the predicted average of a life a birth, reflects the quality of life faced by children at birth

Global Carrying Capacity Estimates of Earth’s carrying capacity are around 10 – 15 billion, roughly 7 billion on Earth now. Ecological Footprint- summarizes the aggregate land and water area appropriated by each nation to produce all the resources it consumes and to absorb all the waste is generates – Six Ecologically Productive Areas Used to Calculate a Countries Ecological Footprint Arable Land Pasture Forest Ocean Built-Up Land Fossil Energy – Ecologically productive area is converted to amount of land per person and totaled for the planet, roughly 2 hectares per person Back to the bullet, put Ecological Capacity- the actual resource base of each country – The United States of America has an ecological footprint of 8.4 hectares per person but has only 6.2 hectors per person of available ecological capacity – The United States of America population is already above carrying capacity

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