Transcript Ecology
Population Ecology and Ecosystems Concepts and Applications: Chapters 40 & 43 Basic Concepts: Chapters 27 & 30 http://darwin.bio.uci.edu/~sustain/bio65/lec16/b65lec16.htm Population Ecology Ecology Ecology: The study of how organisms interact with one another and with their environment • Certain ecological principles govern the growth and sustainability of all populations • Human populations are no exception Population Ecology Human Population Problems • Over 6 billion people alive • About 2 billion live in poverty • Most resources are consumed by the relatively few people in developed countries Population Ecology Population • A group of individuals of the same species occupying a given area • Can be described by demographics – Vital statistics such as size, density, distribution, and age structure Population Ecology Population Age Structure • Divide population into age categories • Population’s reproductive base includes members of the reproductive and prereproductive age categories Population Ecology Density & Distribution • Number of individuals in some specified area of habitat clumped • Crude density information is more useful if combined with distribution data nearly uniform Fig 40.2 random Population Ecology Determining Population Size • Direct counts are most accurate but seldom feasible • Can sample an area, then extrapolate • Capture-recapture method is used for mobile species Mark and Recapture # marked Captured Total Captured = Number released Total Pop Population Ecology Assumptions in Capture-Recapture • Marking has no effect on mortality • Marking has no effect on likelihood to being captured • There is no immigration or emigration between sampling times Population Ecology Changes in Population Size • Immigration adds individuals • Emigration subtracts individuals • Births add individuals • Deaths subtract individuals Population Ecology Zero Population Growth- ZPG • Interval in which number of births is balanced by number of deaths • Assume no change as a result of migration • Population size remains stable Population Ecology Per Capita Rates • Rates per individual • Total number of events in a time interval divided by the number of individuals • Per capita birth rate per month = Number of births per month Population size Population Ecology Exponential GrowthFig 40.4 • Population size expands by ever increasing increments during successive intervals • The larger the population gets, the more individuals there are to reproduce Population Ecology r • Net reproduction per individual per unit time • Variable combines per capita birth and death rates (assuming both constant) • Can be used to calculate rate of growth of a population Population Ecology Exponential Growth Equation G = rN • G is population growth per unit time • r is net reproduction per individual per unit time • N is population size Population Ecology Biotic Potential • Maximum rate of increase per individual under ideal conditions • Varies between species • In nature, biotic potential is rarely reached Population Ecology Limiting Factors • Any essential resource Space that is in short supply Food • All limiting factors acting Shelter on a population dictate Temperature sustainable population Mates size Pollution Disease Population Ecology Carrying Capacity (K) • Maximum number of individuals that can be sustained in a particular habitat • Logistic growth occurs when population size is limited by carrying capacity Population Ecology Logistic Growth Equation G = rmax N (K-N/K) • G = population growth per unit time • rmax = maximum population growth rate per unit time • N = number of individuals • K = carrying capacity Population Ecology Logistic Growth • As size of the population increases, rate of reproduction decreases • When the population reaches carrying capacity, population growth ceases carrying capacity Time Population Ecology Overshooting Capacity • Population may temporarily increase above carrying capacity • Overshoot is usually followed by a crash; dramatic increase in deaths Fig 40.7 Population Ecology Resetting the Carrying Capacity • Major changes in environment can change the carrying capacity of a local system Fig 40.6 Population Ecology Density-Dependent Controls • Logistic growth equation deals with density-dependent controls • Limiting factors become more intense as population size increases • Disease, competition, parasites, toxic effects of waste products Population Ecology Density-Independent Controls • Factors unaffected by population density • Natural disasters or climate changes affect large and small populations alike Population Ecology Life History Patterns • Patterns of timing of reproduction and survivorship • Vary among species • Summarized in survivorship curves and life tables Population Ecology Life Table • Tracks age-specific patterns • Population is divided into age categories • Birth rates and mortality risks are calculated for each age category Population Ecology Survivorship Curves Fig 40.8 Population Ecology Human Population Growth • Population now exceeds 6 billion • Rates of increase vary among countries • Average annual increase is 1.26 percent • Population continues to increase exponentially Population Ecology Human Population Growth 1999 1975 domestication of plants, animals 9000 B.C. (about 11,000 years ago) agriculturally based urban societies beginning of industrial, scientific revolutions Fig. 40.9, p. 695 Population Ecology How Humans have Side-Stepped density dependent controls • Expanded into new habitats • Agriculture increased carrying capacity; use of fossil fuels aided increase • Hygiene and medicine lessened effects of density-dependent controls Population Ecology Future Growth • Exponential growth cannot continue forever • Breakthroughs in technology may further increase carrying capacity • Eventually, densitydependent factors will slow growth Population Momentum • Lowering fertility rates cannot immediately slow population growth rate. Why? • If every couple had just two children, population would still keep growing for another 60 years Population Ecology Resource Consumption • United States has 4.7 percent of the world’s population • Americans have a disproportionately large effect on the world’s resources • Per capita, Americans consume more resources and create more pollution than citizens of less developed nations Population Ecology Effects of Economic Development • Total fertility rates (TFRs) are highest in developing countries, lowest in developed countries • When individuals are economically secure, they are under less pressure to have large families Population Ecology Slowing Growth in China • World’s most extensive family planning program • Government rewards small family size, penalizes larger families, provides free birth control, abortion, sterilization • Since 1972, TFR down to 1.8 from 5.7 Community Ecology Community Ecology • Community: Populations of all species in a habitat. • Niche: Sum total of all a species activities and relationships as species do what they do. – Fundamental, Realized Community Ecology Types of Interactions Who benefits? • • • • • • Neutral Commensalism Mutualism Competition Predation Parasitism Spp 1 0 Y Y N Y Y Spp 2 0 0 Y N N N Community Ecology Competition • Competitive Exclusion – Paramecium • Resource Partitioning – Fruit eating birds, Barnacles Community Ecology Predator-Prey Interactions • The Classic Lynx / Hare system Ecosystems Ecosystems • Energy is transferred from the SUN to all organisms • Primary Producers • Consumers • Decomposers • Energy is LOST with each transition Ecosystems Food Webs MARSH HAWK HIGHER TROPHIC LEVELS Complex array of carnivores, omnivores and other consumers. Many feed at more than one trophic level continually, seasonally, or when an opportunity presents itself CROW UPLAND SANDPIPER GARTER SNAKE FROG SPIDER SECOND TROPHIC LEVEL Primary consumers (e.g., herbivores) FIRST TROPHIC LEVEL Primary producers • A composite picture of an ecosystem’s membership and their interaction WEASEL CLAYCOLORED SPARROW EARTHWORMS, INSECTS (E.G., PRAIRIE VOLE GRASSHOPPPERS, CUTWORMS) BADGER POCKET GOPHER COYOTE GROUND SQUIRREL Fig. 43.6, p. 740 Do not post photos on Internet Ecosystems Food Webs can be Disrupted • Natural Disasters • External inputs – Pesticides, Pollution Ecosystems ATMOSPERE The Hydrologic Cycle wind driven water vapor 40,000 evaporation from ocean 425,000 precipitation onto land 111,000 evaporation from land plants (evapotranspiration) 71,000 precipitation into ocean 385,000 surface and groundwater flow 40,000 LAND OCEAN Main Reservoirs Volume (103 cubic kiometers) Oceans 1,370,000 Polar ice, glaciers 29,000 Groundwater 4,000 Lakes, rivers 230 Soil moisture 67 Atmosphere (water vapor) 14 Fig. 43.14, p. 746 Ecosystems Other Cycles • Carbon • Nitrogen • Phosphorus Quiz