Growth of Populations CHAPTER 22 Population Ecology Population ecology is the study of the number of organisms in a particular area 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 natality and mortality and immigration and emigration rates Natality- birth rate Mortality- death rate Immigration- organisms entering an area Emigration- organisms leaving an area All of these are affected by environmental factors Population Calculations To find the change in a population: P = [N+I] [M+E] N=natality I = immigration M=mortality E = emigration To find the density of a popluation: 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 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 Population Growth Has its Limits Growth is limited by essential resources and other environmental factors Populations cannot increase in size indefinitelylimits 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 community are part of a whole). Water, space, food, temperature, soil, disease, 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 Abiotic Factors are Density-Independent Density-Independent Factors affect all populations regardless of their density Temperature, storms, flood, drought, or other natural habitat disruptions Biotic Factors: living aspects of the environment. Plants, animals, etc. Biotic Factors Biotic Factors are Density-Dependent 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 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 Population Growth Varies for Due to Changes in the Environment 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 Population Growth Varies for Due to Changes in the Environment Which will we experience? The jury is still out. How are we different that the rest of the Animal Kingdom Human Population Growth On a range of 450 acres there are a total of 1275 jackrabbits. Studies indicate the following rates for this population: mortality per yearnatality per year emigration per yearimmigration -150 per year A.Is the population increasing or decreasing? B.At what rate per year? C.Predict the population at the end of four years. D.What will happen to the producers during the four years? E.What is the density of rabbits at the start? F.What is the density of rabbits after 4 years? A team of biologists studied a population of box turtles in an Ohio wood lot for a period of 10 years. They determined that the natality averaged 40 per year, the mortality 30 per year, immigration 3 per year, and emigration 8 per year. A.Was the population increasing or decreasing? B.Was the area supplying box turtles to other places or vice versa? C.What was the average annual change due to emigration and immigration? D.If the initial population was 15 turtles, what was the population at the end of 10 years? E.Assume the wood lot was 5 acres. Calculate the density of the turtles at the start of the 10 years and at the end