Population Ecology 213.ppt
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Population Ecology 08/11/24 1 Population Ecology I. Characteristics of Populations II. Demography and Survivorship III. Models of Population Growth IV. Factors That Limit Population Size V. Life Histories VI....
Population Ecology 08/11/24 1 Population Ecology I. Characteristics of Populations II. Demography and Survivorship III. Models of Population Growth IV. Factors That Limit Population Size V. Life Histories VI. The Human Population 08/11/24 2 Learning Objectives 1. Define populations 2. Explain the factors that determine the distribution pattern of a population 3. Describe uses of cohort life tables 4. Compare and contrast the three types of survivorship curves 5. Describe the applications and limitations of the exponential growth model 6. Explain the terms of the logistic growth equation and how population growth stabilizes 08/11/24 3 Learning Objectives 7. Identify density dependent and density independent factors that control population size 8. Explain the causes of boom-bust cycles 9. Compare and contrast opportunistic and equilibrial life histories 10. Evaluate the growth and impact of human populations globally and locally. 08/11/24 4 I. Characteristics of Populations A. A population is a group of organisms of the same species living in the same location at the same time. B. Population Density is an estimate of the number of individuals per unit of area. This is usually estimated using sampling techniques. 08/11/24 5 Quadrat Sampling vs Mark- Recapture This method is best Used to estimate for sampling population size of sessile organisms moving animals like plants N= Total Marked x Total 2nd N= Total Area x Mean Catch Quadrat Count Total Recaptured Quadrat area (marked) 08/11/24 6 C. Dispersion Patterns refer to the how the members of a population are distributed in their habitat. Types: 1. Clumped Pattern: This is the grouping of individuals in several clusters that results from: a) Social interactions b) Uneven distribution of resources. 08/11/24 7 2. Uniform Pattern: characterized by the even spacing of organisms in an area. This results from a) Resource competition b) Territorial behaviors 3. Random patterns are rare but may happen in dynamic environments such as intertidal zones. 08/11/24 8 II. Demography and Life Tables A. Demography 1. Demography is the study of the vital statistics of a population and how they change over time 2. Death rates and birth rates are of particular interest to demographers 08/11/24 9 B. Life Tables 1. These depict the mortality and survival of a cohort at specific time intervals. 2. A cohort is a group nx : the number of surviving cohort individuals of individuals born lx : the survival probability in the same time from birth to a specific age period dx : the age-specific mortality qx : the age-specific mortality rate 08/11/24 10 C. A survivorship curve is a graphic way of representing the data in a life table The survivorship curve for gray squirrels shows a relatively constant death rate 08/11/24 11 D. Ecologists recognize three types of survivorship curves: Type I: Low infant mortality, survival through most of the life span (humans and large mammals) Type II: Relatively constant mortality rates (birds, rodents, some plants) Type III: High infant mortality, low life expectancy (fish, oysters, most invertebrates) 08/11/24 12 III. Models of Population Growth A. The model of exponential growth predicts the rate of change in the size of a population over time. The factor included in this model are dN/dt = rate of change r = intrinsic rate of increase N = population size at a specific time dN/dt = r N 08/11/24 13 B. The exponential model predicts the growth of populations that 1. Are at low density 2. Colonize a new area 3. Live in a favorable environment with abundant resources 4. Are controlled by birth vs. death rates 08/11/24 14 5. An example is the introduction of reindeer to St. Paul island in Alaska. The population grew from 4 males and 22 females to a herd of 2000 in only 30 years. C. Logistic Growth. This model predicts the growth of a population that lives in an area with limited resources such as food, water, shelter, and mates. K is the carrying capacity of a place dN (K N) rmax N dt K Logistic growth examples: 1. Elephant and fur seals. 2. Most vertebrates. 08/11/24 16 08/11/24 17 IV. Factors That Limit Population Size A. Density-dependent Factors. These factors affect a greater number of individuals as population density increases. Examples: 1. Depletion of food and water 2. Increased waste production 3. Disease outbreaks 4. Spread of parasites 08/11/24 18 08/11/24 19 B. Density-dependent factors are the main cause of “boom- and-bust” cycles. Example: The lynx and snowshoe hare 10-year cycles. - The lynx population is limited by the abundance of prey. -The hare population is controlled by its food supply (plants). 08/11/24 20 B. Density-independent factors are those that limit population size regardless of population density. Examples: 1. Floods & droughts 2. Extreme cold or heat 3. Fires 4. Human disturbance 08/11/24 21 V. Life Histories An organism’s life history comprises the traits that affect its schedule of reproduction and survival – The age at which reproduction begins – How often the organism reproduces – How many offspring are produced during each reproductive cycle Life history traits are evolutionary outcomes reflected in the development, physiology, and behavior of an organism 08/11/24 22 08/11/24 23 VI. Human Populations A. News headlines concerning ecology and human populations: 1. Deforestation 2. Species extinction 3. Pollution, oil spills 4. Climate change Arguably, the root cause of all ecological problems is the rapid increase of the human population. 08/11/24 24 B. Human Population Control 1. There are over 7.7 billion people in this world 2. The human population increases by 2.2 humans/sec 3. Age structure diagrams can predict a population’s growth trends 08/11/24 25 To maintain population stability, a regional human population can exist in one of two configurations – Zero population growth = High birth rate – High death rate – Zero population growth = Low birth rate – Low death rate The demographic transition is the move from the first state to the second state Unlike other organisms, we can regulate our population growth through social changes 08/11/24 26 B. Human population growth is no longer exponential but still very rapid. When will this growth level off? Population ecologists predict a global population of 8.110.6 billion people in 2050 What will be the factors controlling human population growth? Our carrying capacity could potentially be limited by food, space, nonrenewable resources, or buildup of wastes. 08/11/24 27 C. A Planet in Crisis? 90% of world-wide fish stocks are overfished 1:10 people lack access to clean water 2:7 people in the world live on less than $2/day 1:8 people are chronically malnourished Did you know the USA population (only 5% of the world’s population)… - Consumes 25-30% of fossil fuel? - Consumes 40% of necessary and luxury goods? - Generates 8X more waste than a person in an undeveloped country? 08/11/24 28