Population Ecology Honors Biology Ms. Day Lecture #46

Population ecology = study of populations Population = group of SAME individuals (SAME species) living in the SAME general area at the SAME time Population Ecology

Populations Three key features of populations: 1.Size number of individuals in a given area 2.Density measurement of population per unit area or unit volume 3.Dispersion describes their spacing relative to each other

+ 1. Size depends on… Growth Rate: Birth Rate – Death Rate = Rate of natural increase (b - d = r)

+ 2. Density Population density = number of individuals / unit of area

Dispersion of individuals clumped even (uniform) random

Clumped distribution influenced by resource availability most common Uniform distribution influenced by social interactions such as territoriality Random distribution the position of each individual is independent of other individuals

2 Types of Population Growth  Exponential Growth = – population grows as if there are no limitations – Population gets very LARGE – J-curve – Not often seen in nature! – Ex: HUMAN POPULATION, ELEPHANTS

What Factors Can Affect Population Growth? Limiting factor any biotic or abiotic factor that restricts the size of the population in a given area Examples: – Amount of water, Amount of food, Temperature

Factors That Affect the Carrying Capacity Two types: 1)Density-dependent limiting factor 2)Density-independent limiting factor Carrying capacity Maximum # of individuals that a population can sustain in a given environment without destroying the habitat

Liming Factor(s) SET the carrying capacity…

Limiting Factors Control Population Sizes Density-dependent factors – Factors that limit a population’s size based on HOW MANY individuals are present Examples: Food supplies, waste, population-crowding diseases, H 2 O, mates, predators Density-independent factors have nothing to do with the population size – THINK: NATURE – Floods, droughts, earthquakes, other natural disasters and weather conditions

Population Growth (con’t) 2. Logistic Growth population growth slows to zero and population size tends to stabilize because of environmental resistance (Limiting factors) S-curve Set by carrying capacity Ex: yeast, bacteria K

Number of generations Population size (N) Carrying capacity 1,500 2,000 1, Logistic growth Exponential growth 2 Population curves

Exponential Growth (J-shaped) Logistic (S-shaped)