Growth of Populations CHAPTER 22

How Many Organisms Live in a Particular Environment, and Why? Population ecology is the study of the number of organisms in a particular place Population ecology is essential for solving real- world problems, such as protecting endangered species or controlling pest species

What Is a Population? A population is a group of interacting individuals of a single species located within a particular area Population size: total number of individuals in the population Population density: the number of individuals per unit of area. Ex: 200 humans/square mile There are three populations in this picture

Changes in Population Size Whether a population increases or decreases in size depends on the birth and death rates and immigration and emigration rates Birth and death rates and immigration and emigration rates are all affected by environmental factors

Calculating Changes in Population Size ΔP = [N+I] – [M+E] N=natality I = immigration M=mortality E = emigration Density= # or organisms/ unit of area

Exponential Growth: J-Shaped Growth Patterns Endless exponential growth of a population is limited by the availability of resources and is not seen under natural conditions Doubling time: The time it takes a population to double in size

Erosion of a gully in South Australia caused by rabbits The No. 1 rabbit-fence in Western Australia (1926) Rabbits around a waterhole in the myxomatosis trial site on Wardang Island in 1938 "The introduction of a few rabbits could do little harm and might provide a touch of home, in addition to a spot of hunting.” - Thomas Austin

Population Growth Has its Limits Growth is limited by essential resources and other environmental factors Populations cannot increase in size indefinitely—limits exist

Limiting Factors A Limiting Factor is any living or non-living factor that restricts the existence, numbers, reproduction, or distribution of organisms. Factors that limit one population will affect other populations (Remember all living things in a committee are part of a whole). Water, space, food, temperature, soil, etc.

Population Growth Has its Limits Space and nutrients are important limiting factors in the population growth of an organism Habitat is the type of environment in which an organism lives and is an environmental factor that limits population growth

Abiotic Factors: Physical and Chemical Characteristics of the environment (Non-living) Ex: Solar Energy, Oxygen, CO 2, Water, Temperature, Humidity, pH, Nitrogen, Phosphorus Abiotic Factors

Biotic Factors: living aspects of the environment. Plants, animals, etc. Biotic Factors

Logistic Population Growth: S-Shaped Growth Pattern Logistic growth: – What we see in nature most of the time – Represented by an S-shaped curve – Consideration that growth rates change as resources become limited Carrying capacity: – The maximum population size that can be sustained in an environment – At the carrying capacity, the population growth rate is zero

Density-Dependent Factors Birth rates and death rates are density-dependent because they change as the density of the population changes Density-Dependent Factors include disease, competition, and parasites Biotic factors

Density-Independent Factors Density-Independent Factors affect all populations regardless of their density Abiotic factors Temperature, storms, flood, drought, or other natural habitat disruptions

Population Cycles In a population cycle, the population sizes of two or more species change together because at least one of the two is influenced by the other

Predator Prey relationships encourage the health of an ecosystem: Usually, in prey populations, the weak, young, old, or injured members are caught Keeps population size within the limits of available resources Improves the genetic make up of the surviving members of that population

Patterns of Population Growth: Irregular Fluctuations Populations of the same species may experience different patterns of growth depending on the environment

In1800 estimated 100,000 breeding pairs present By the early 1960s, population counts indicated that only 417 breeding pairs of eagles remained in the lower 48 states Patterns of Population Growth: Irregular Fluctuations

Which will we experience? The jury is still out. How are we different that the rest of the animal Kingdom Human Population Growth