Populations

What is a population? A population is a group of individuals of the same species living in a defined area.

How Populations Grow Characteristics of Populations 1. Geographic distribution – area inhabited, species specific 2. density – number of individuals per unit area – Fig. 5-1 3. growth rate – determined by the number of births, number of deaths, number of individuals entering and leaving 4. age structure – determined by how many individuals of different ages make up a given population

How Populations Grow Population Growth – Fig. 5-2 1. Immigration – movement of individuals into an area 2. Emigration – movement of individuals out of an area

How Populations Grow Population Growth (cont.) 3. Exponential Growth – the geometric increase of a population as it gr0ws in an ideal, unlimited environment - Fig. 5-3(J- shape cure) What keeps population from growing exponentially?

How Populations Grow Population Growth (cont.) 4. Logistic Growth – describes population growth that levels off as population size approaches carrying capacity – Fig. 5-4 (S- shape curve)

How Populations Grow Population Growth (cont.) 4. Logistic Growth (cont.) 1. carrying capacity – maximum population size that a particular environment can support at a particular time with no degradation of the habitat 2. most species follow this growth model

Limits to Growth Limiting Factors – factors that decrease population growth – Fig. 5-5 Competition, Predation, Parasitism and disease are examples of density-dependent limiting factors Drought and other climate extremes and human disturbances are examples of density-independent limiting factors

Limits to Growth Density-Dependent – a death rate that rises or a birth rate that declines as population density rises 1. Competition – organisms compete for food, shelter, mates a. Intraspecific competition – occurs between members of the same species for limited resources

Limits to Growth Density-Dependent – a death rate that rises or a birth rate that declines as population density rises 1. Competition (cont.) b. Interspecific competition – occurs between members of different species for limited resources – this is a major force behind evolutionary change c. Only one species can occupy a niche in the same place at the same time (niche – species’ use of biotic and abiotic resources)

Limits to Growth

Limits to Growth Density-Dependent (cont.) 2. Predation – an interaction between species in which one species, the predator, eats the other, the prey – Fig. 5-7

Limits to Growth Density-Dependent (cont.) 3. parasitism – a symbiotic relationship in which the parasite benefits at the expense of the host – Fig. 5-8

Limits to Growth Density-Independent Factors – any factor that affects a population by the same percentage, regardless of density 1. Drought and other climate extremes 2. Human disturbances

Human Population Growth What type of growth pattern is shown in Fig. 5-10?

Human Population Growth Patterns of Population Growth – What factors explain why populations in different countries grow at different rates? 1. Demographic transition – change in a population from high birth and death rates to low birth and death rates – Fig. 5-11

Human Population Growth Patterns of Population Growth (cont.) 2. Age structure – numbers of people in different age groups in the population

Human Population Growth Future population Growth – Will the human population grow at its current rate, or will it level out to a logistic growth curve and become stable?