53_lecture_presentation_0.ppt

Chapter 53 Population Ecology PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cu...

Chapter 53 Population Ecology PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview Population ecology is the study of populations in relation to environment, including environmental influences on density and distribution, age structure, and population size. A population is a group of individuals of a single species living in the same general area. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Dynamic biological processes influence population density, dispersion, and demographics Density is the number of individuals per unit area or volume. Dispersion is the pattern of spacing among individuals within the boundaries of the population. Density is the result of an interplay between processes that add individuals to a population and those that remove individuals. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Immigration is the influx of new individuals from other areas. Emigration is the movement of individuals out of a population. In most cases, it is impractical or impossible to count all individuals in a population. Sampling techniques can be used to estimate densities and total population sizes. Population size can be estimated by either extrapolation from small samples, an index of population size, or the Mark-Recapture Method. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Population dynamics Births Deaths Births and immigration Deaths and emigration add individuals to remove individuals a population. from a population. Immigration Emigration Patterns of Dispersion Environmental and social factors influence spacing of individuals in a population. In a clumped dispersion, individuals aggregate in patches. A clumped dispersion may be influenced by resource availability and behavior. A uniform dispersion is one in which individuals are evenly distributed. It may be influenced by social interactions such as territoriality. In a random dispersion, the position of each individual is independent of other individuals. It occurs in the absence of strong attractions or repulsions. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Patterns of dispersion within a population’s geographic (a) Clumped range (b) Uniform (c) Random Demographics Demography is the study of the vital statistics of a population and how they change over time. Death rates and birth rates are of particular interest to demographers. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Life Tables & Survivorship Curves A life table is an age-specific summary of the survival pattern of a population. It is best made by following the fate of a cohort, a group of individuals of the same age. A survivorship curve is a graphic way of representing the data in a life table. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Survivorship curves for squirrels shows relatively constant death rate 1,000 Number of survivors (log scale) 100 Females 10 Males 1 0 2 4 6 8 10 Age (years)  Survivorship curves can be classified into three general types: – Type I: low death rates during early and middle life, then an increase among older age groups – Type II: the death rate is constant over the organism’s life span – Type III: high death rates for the young, then a slower death rate for survivors Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Survivorship Curves Number of survivors (log scale) 1,000 I 100 II 10 III 1 0 50 100 Percentage of maximum life span Reproductive Rates For species with sexual reproduction, demographers often concentrate on females in a population. A reproductive table, or fertility schedule, is an age-specific summary of the reproductive rates in a population. It describes reproductive patterns of a population. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Life history traits are products of natural selection 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. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Evolution and Life History Diversity Life histories are very diverse. Species that exhibit semelparity, or big-bang reproduction, reproduce once and die. Species that exhibit iteroparity, or repeated reproduction, produce offspring repeatedly. Highly variable or unpredictable environments likely favor big-bang reproduction, while dependable environments may favor repeated reproduction. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings “Trade-offs” and Life Histories Organisms have finite resources, which may lead to trade-offs between survival and reproduction. In animals, parental care of smaller broods may facilitate survival of offspring. Some plants, like the dandelion, produce a large number of small seeds, ensuring that at least some of them will grow and eventually reproduce. Other types of plants, like the coconut tree, produce a moderate number of large seeds that provide a large store of energy that will help seedlings become established. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Variation in the size of seed crops in plants (a) Dandelion (b) Coconut palm The exponential model describes population growth in an idealized, unlimited environment It is useful to study population growth in an idealized situation. Idealized situations help us understand the capacity of species to increase and the conditions that may facilitate this growth. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Zero population growth occurs when the birth rate equals the death rate. Most ecologists use differential calculus to express population growth as growth rate at a particular instant in time: N  rN t where N = population size, t = time, and r = per capita rate of increase = birth – death Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Exponential Growth Exponential population growth is population increase under idealized conditions. Under these conditions, the rate of reproduction is at its maximum, called the intrinsic rate of increase. Exponential population growth results in a J- shaped curve Exponential Growth is not sustainable. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Exponential Growth Model 2,000 dN = 1.0N dt Population size (N) 1,500 dN = 0.5N dt 1,000 500 0 0 5 10 15 Number of generations The J-shaped curve of exponential growth characterizes some rebounding populations 8,000 Elephant population 6,000 4,000 2,000 0 1900 1920 1940 1960 1980 Year The logistic model describes how a population grows more slowly as it nears its carrying capacity Exponential growth cannot be sustained for long in any population. A more realistic population model limits growth by incorporating carrying capacity. Carrying capacity (K) is the maximum population size the environment can support. In the logistic population growth model, the rate of increase declines as carrying capacity is reached. The logistic model of population growth produces a sigmoid (S-shaped) curve. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Logistic Growth model Exponential growth 2,000 dN = 1.0N dt Population size (N) 1,500 K = 1,500 Logistic growth 1,000 dN 1,500 – N = 1.0N dt 1,500 500 0 0 5 10 15 Number of generations The Logistic Model and Real Populations The growth of laboratory populations of paramecia fits an S-shaped curve. These organisms are grown in a constant environment lacking predators and competitors. Some populations overshoot K before settling down to a relatively stable density. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The growth of laboratory populations fits an S-shaped curve which hovers around the Carrying Capacity of the area. Number of Paramecium/mL Number of Daphnia/50 mL 1,000 180 150 800 120 600 90 400 60 200 30 0 0 0 5 10 15 0 20 40 60 80 100 120 140 160 Time (days) Time (days) (a) A Paramecium population in the lab (b) A Daphnia population in the lab The Logistic Model and Life Histories Life history traits favored by natural selection may vary with population density and environmental conditions. K-selection = density-dependent selection, selects for life history traits that are sensitive to population density. r-selection = or density-independent selection, selects for life history traits that maximize reproduction. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Many factors that regulate population growth are density dependent There are two general questions about regulation of population growth: – What environmental factors stop a population from growing indefinitely? – Why do some populations show radical fluctuations in size over time, while others remain stable? Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Population Change and Population Density In density-independent populations, birth rate and death rate do not change with population density. In density-dependent populations, birth rates fall and death rates rise with population density. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Density-Dependent Population Regulation Density-dependent birth and death rates are an example of negative feedback that regulates population growth. They are affected by many factors, such as competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factors. In crowded populations, increasing population density intensifies competition for resources and results in a lower birth rate. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Decreased reproduction at high population densities Percentage of juveniles producing lambs 100 80 60 40 20 0 200 300 400 500 600 Population size Territoriality In many vertebrates and some invertebrates, competition for territory may limit density. Cheetahs are highly territorial, using chemical communication to warn other cheetahs of their boundaries. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Territoriality (a) Cheetah marking its territory (b) Gannets  Disease, Predation, & Toxic Wastes Population density can influence the health and survival of organisms. In dense populations, pathogens can spread more rapidly. As a prey population builds up, predators may feed preferentially on that species. Accumulation of toxic wastes can contribute to density-dependent regulation of population size. For some populations, intrinsic (physiological) factors appear to regulate population size. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Population Dynamics The study of population dynamics focuses on the complex interactions between biotic and abiotic factors that cause variation in population size. Long-term population studies have challenged the hypothesis that populations of large mammals are relatively stable over time. Weather can affect population size over time. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Changes in predation pressure can drive population fluctuations 50 2,500 Wolves Moose Number of wolves Number of moose 40 2,000 30 1,500 20 1,000 10 500 0 0 1955 1965 1975 1985 1995 2005 Year Population Cycles: Scientific Inquiry Some populations undergo regular boom-and- bust cycles. Lynx populations follow the 10 year boom-and- bust cycle of hare populations. Three hypotheses have been proposed to explain the hare’s 10-year interval. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Snowshoe hare 160 Number of hares Number of lynx (thousands) 120 (thousands) 9 Lynx 80 6 40 3 0 0 1850 1875 1900 1925 Year  Hypothesis 1: The hare’s population cycle follows a cycle of winter food supply. If this hypothesis is correct, then the cycles should stop if the food supply is increased. Additional food was provided experimentally to a hare population, and the whole population increased in size but continued to cycle. No hares appeared to have died of starvation. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Hypothesis 2: The hare’s population cycle is driven by pressure from other predators. In a study conducted by field ecologists, 90% of the hares were killed by predators. These data support this second hypothesis. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Hypothesis 3: The hare’s population cycle is linked to sunspot cycles. Sunspot activity affects light quality, which in turn affects the quality of the hares’ food. There is good correlation between sunspot activity and hare population size. The results of all these experiments suggest that both predation and sunspot activity regulate hare numbers and that food availability plays a less important role. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Immigration, Emigration, and Metapopulations Metapopulations are groups of populations linked by immigration and emigration. High levels of immigration combined with higher survival can result in greater stability in populations. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The human population is no longer growing exponentially but is still increasing rapidly No population can grow indefinitely, and humans are no exception. The human population increased relatively slowly until about 1650 and then began to grow exponentially. Though the global population is still growing, the rate of growth began to slow during the 1960s. Most of the current global population growth is concentrated in developing countries. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Human population growth 7 Human population (billions) 6 5 4 3 2 The Plague 1 0 8000 4000 3000 2000 1000 0 1000 2000 B.C.E. B.C.E. B.C.E. B.C.E. B.C.E. C.E. C.E. Regional Patterns of Population Change 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 toward the second state. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Age Structure One important demographic factor in present and future growth trends is a country’s age structure. Age structure is the relative number of individuals at each age. Age structure diagrams can predict a population’s growth trends. They can illuminate social conditions and help us plan for the future. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Age-structure pyramids for the human population of three countries Rapid growth Slow growth No growth Afghanistan United States Italy Male Female Age Male Female Age Male Female 85+ 85+ 80–84 80–84 75–79 75–79 70–74 70–74 65–69 65–69 60–64 60–64 55–59 55–59 50–54 50–54 45–49 45–49 40–44 40–44 35–39 35–39 30–34 30–34 25–29 25–29 20–24 20–24 15–19 15–19 10–14 10–14 5–9 5–9 0–4 0–4 10 8 6 4 2 0 2 4 6 8 10 8 6 4 2 0 2 4 6 8 8 6 4 2 0 2 4 6 8 Percent of population Percent of population Percent of population Estimates of Earth’s Carrying Capacity How many humans can the biosphere support? The carrying capacity of Earth for humans is uncertain. The average estimate is 10–15 billion. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Limits on Human Population Size The ecological footprint concept summarizes the aggregate land and water area needed to sustain the people of a nation. It is one measure of how close we are to the carrying capacity of Earth. Countries vary greatly in footprint size and available ecological capacity. Our carrying capacity could potentially be limited by food, space, nonrenewable resources, or buildup of wastes. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Review: Population Growth Curve Population size (N) K = carrying capacity dN K–N = rmax N dt K Number of generations You should now be able to: 1. Define and distinguish between the following sets of terms: density and dispersion; clumped dispersion, uniform dispersion, and random dispersion; life table and reproductive table; Type I, Type II, and Type III survivorship curves; semelparity and iteroparity; r-selected populations and K- selected populations. 2. Explain how ecologists may estimate the density of a species. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  3. Explain how limited resources and trade-offs may affect life histories. 4. Compare the exponential and logistic models of population growth. 5. Explain how density-dependent and density- independent factors may affect population growth. 6. Explain how biotic and abiotic factors may work together to control a population’s growth. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings