POPULATION ECOLOGY

Objectives: I will be able to describe differences between exponential and logistic models of population growth. I will be able to discuss characteristics of human population growth.

Intro: On a scrap piece of paper sketch two graphs: Linear growth graph Exponential growth graph What will you plot on the x-axis? What will you plot on the y-axis? Give your graphs appropriate titles.

Population Ecology Population = organisms of the same species that live in the same area and interbreed. Size of a population (N) = total number of individuals in the population. Density of a population = total number of individuals per area occupied (i.e. 100 mosquitos/m2). Dispersion = describes how individuals in a population are distributed (clumped, uniform, or random). Density: the number of organisms in a given area Distribution: how the organisms are spaced in the area

Dispersion Patterns Density: the number of organisms in a given area Distribution: how the organisms are spaced in the area

What causes these populations to use this pattern? What distribution pattern do you see? What causes these populations to use this pattern? Clumped distribution acts as a mechanism against predation as well as an efficient mechanism to trap or corner prey.

Population Sizes Fluctuate Over Time Due to environmental conditions (presence of predators, immigration/emigration, availability of nutrients, etc.). Growing Increase due to births, immigration; decrease due to deaths, emigration Shrinking Boom and bust

Exponential Population Growth: “J-curve” Occurs under ideal conditions when there are no limits to the size to which the population can grow (unlimited water, food, living space, etc.). Rare.

Exponential Growth Growth Rate of E. coli d = delta or change   d = delta or change N = Population size t = time rmax = maximum rate of increase Population Size, N One of the most common examples of exponential growth deals with bacteria.  Bacteria can multiply at an alarming rate when each bacteria splits into two new cells, thus doubling.  For example, if we start with only one bacteria which can double every hour since it reproduces asexually, by the end of one day we will have over 16 million bacteria. http://www.regentsprep.org/Regents/math/ALGEBRA/AE7/ExpDecayL.htm Time (hours)

Logistic Population Growth: “S-curve” Occurs when resources and space are limited. Carrying capacity = maximum number of organisms of a population that the environment can support for indefinite period of time. Factors that limit carrying capacity = limiting factors. Types of limiting factors: density-dependent and density-independent . Label the following limiting factors as density-dependent or density-independent: earthquake food and water availability flood disease or parasites competition or crowding frost

Some populations do not have a stable carrying capacity Logistic Model carrying capacity Some populations do not have a stable carrying capacity Fits some populations well, but for many there is not stable carrying capacity and populations fluctuate around some long-tem average density (boom and bust cycle)

Logistic Growth d = delta or change N = Population Size t = time   d = delta or change N = Population Size t = time K =carrying capacity rmax = maximum rate of increase Ask: What is the carrying capacity (K ) for AIDS according to this graph? 45,000 as of 1995.

Population Reproductive Strategies r-selected species Exhibit J-shaped curve, Opportunistic species that quickly invade a habitat, Short maturation and lifespan, Many small offspring, No parental care, High death rate. K-selected species Exhibit S-shaped curve, Long maturation & lifespan, Few large offspring, Extensive parental care, Low death rate. Emphasize that these r-selected and opportunistic are synonyms as are K- selected and equilibrial. It’s the synonyms that will give students fits when they are reading and interpreting test questions!

Population Survivorship Curves describe how mortality of individuals in a species varies during their lifetimes. Survivorship curves 25 1000 100 Human (type I) Hydra (type II) Oyster (type III) 10 1 50 Percent of maximum life span 75 Survival per thousand Type I. High death rate in post-reproductive years. Type II. Constant mortality rate throughout life span. Type I curve is flat at the start, reflecting low death rates during early and middle life, then drops steeply as death rates increase among older age groups. Humans and many other large mammals that produce few offspring but provide them with good care often exhibit this kind of curve. Type II curves are intermediate, with a constant death rate over the organism’s life span. This kind of survivorship occurs in Belding’s ground squirrels and some other rodents, various invertebrates, some lizards, and some annual plants. Type III curve drops sharply at the start, reflecting very high death rates for the young, but then flattens out as death rates decline for those few individuals that have survived to a certain critical age. This type of curve is usually associated with organisms that produce very large numbers of offspring but provide little or no care, such as long–lived plants, many fishes, and marine invertebrates. An oyster, for example, may release millions of eggs, but most offspring die as larvae from predation or other causes. Those few that survive long enough to attach to a suitable substrate and begin growing a hard shell will probably survive for a relatively long time. Type III. Very high early mortality but the few survivors then live long (stay reproductive).

Closer Look at Human Population Growth Demographics = study of human population growth characteristics such as: Growth rate = the difference between death rate and birth rate. Fertility = number of offspring a female produces in her reproductive years. Age structure = concerned with how many individuals are in their pre-reproductive, reproductive, and post-reproductive years. Mobility = movement of individuals in or out (in = immigration, out = emigration).

Age Structure Diagrams = show the abundance of individuals of each age. Which country shows slow growth, rapid growth, and no growth? Male Female Age 85+ 80–84 75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0–4 Male Female Age 85+ 80–84 75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0–4 Male Female Afghanistan Italy United States Afganistan – rapid growth, US – slow growth, Italy – no growth 10 8 6 4 2 2 4 6 8 10 8 6 4 2 2 4 6 8 8 6 4 2 2 4 6 8 Percent of population Percent of population Percent of population Always examine the base before making predictions about the future of the population. 16

Global carrying capacity for humans is not known. The human population began exponential growth 1000 years ago due to increases in food supply, reduction in disease, reduction in human waste, and expansion of habitat. Today the human population is no longer growing exponentially but is still increasing rapidly. Global carrying capacity for humans is not known. Ecological footprint = total land and water area needed for all the resources a person consumes. 1.7 hectares (4 acres) per person = sustainable US average per person = 10 hectares (25 acres) Note: 1 hectare = 10,000 square meters or 2.5 acres

Population Growth Rate (Individuals per Year) MATH CONNECTION   Use the table below to calculate the population growth rate of a hypothetical population where the carrying capacity (K) = 1,500 individuals and the maximum rate of increase per year ( rmax) is 1.0. Give your answers to the nearest whole numbers. Population Size (N) Population Growth Rate (Individuals per Year) 500 1000 1500 2000