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CAMPBELL BIOLOGY IN FOCUS Urry • Cain • Wasserman • Minorsky • Jackson • Reece 40 Population Ecology and the Distribution of Organisms Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge © 2014 Pearson Education, Inc. Overview: Discovering Ecology Ecology is the scientific study of the interactions between organisms and the environment These interactions determine the distribution of organisms and their abundance Modern ecology includes observation and experimentation © 2014 Pearson Education, Inc. Figure 40.2 Global ecology Landscape ecology Ecosystem ecology Community ecology Population ecology Organismal ecology © 2014 Pearson Education, Inc. Global ecology is concerned with the biosphere, or global ecosystem, which is the sum of all the planet’s ecosystems Global ecology examines the influence of energy and materials on organisms across the biosphere © 2014 Pearson Education, Inc. Landscape ecology focuses on the exchanges of energy, materials, and organisms across multiple ecosystems A landscape (or seascape) is a mosaic of connected ecosystems © 2014 Pearson Education, Inc. Ecosystem ecology emphasizes energy flow and chemical cycling among the various biotic and abiotic components An ecosystem is the community of organisms in an area and the physical factors with which they interact © 2014 Pearson Education, Inc. Community ecology deals with the whole array of interacting species in a community A community is a group of populations of different species in an area © 2014 Pearson Education, Inc. Population ecology focuses on factors affecting population size over time A population is a group of individuals of the same species living in an area © 2014 Pearson Education, Inc. Organismal ecology studies how an organism’s structure, physiology, and (for animals) behavior meet environmental challenges Organismal ecology includes physiological, evolutionary, and behavioral ecology © 2014 Pearson Education, Inc. Differentiate between biotic and abiotic factors. © 2014 Pearson Education, Inc. Abiotic factors are the nonliving chemical and physical attributes of the environment Biotic factors are the other organisms that make up the living component of the environment © 2014 Pearson Education, Inc. Concept 40.1: Earth’s climate influences the structure and distribution of terrestrial biomes The long-term prevailing weather conditions in an area constitute its climate Four major abiotic components of climate are temperature, precipitation, sunlight, and wind Macroclimate consists of patterns on the global, regional, and landscape level © 2014 Pearson Education, Inc. Describe factors that affect global climate patterns. (i.e. temperature, precipitation, sunlight, and wind) © 2014 Pearson Education, Inc. Figure 40.3a Atmosphere 90N (North Pole) Low angle of incoming sunlight 23.5N (Tropic of Cancer) Sun overhead at equinoxes 0 (Equator) 23.5S (Tropic of Capricorn) Low angle of incoming sunlight 90S (South Pole) Latitudinal variation in sunlight intensity © 2014 Pearson Education, Inc. Global air circulation and precipitation patterns are initiated by intense solar radiation near the equator Warm, wet air rising near the equator creates precipitation in the tropics Dry air descending at 30 north and south latitudes causes desert conditions This pattern of precipitation and drying is repeated at the 60 north and south latitudes and the poles © 2014 Pearson Education, Inc. Variation in the speed of Earth’s rotation at different latitudes results in the major wind patterns Trade winds blow east to west in the tropics Westerlies blow west to east in temperate zones © 2014 Pearson Education, Inc. Figure 40.3ba 66.5N (Arctic Circle) 60N 30N Westerlies Northeast trades 0 Southeast trades 30S Westerlies 60S 66.5S (Antarctic Circle) Global air circulation and precipitation patterns © 2014 Pearson Education, Inc. Figure 40.3bb 30N Descending dry air absorbs moisture. Ascending moist air releases moisture. 0 Global air circulation and precipitation patterns © 2014 Pearson Education, Inc. Regional Effects on Climate Climate (in a particular area of the biosphere) is affected by seasonality, large bodies of water, and mountains © 2014 Pearson Education, Inc. Define a biome. How can you predict what type of biome an abiotic factor may be found in? © 2014 Pearson Education, Inc. Climate and Terrestrial Biomes Biomes are major life zones characterized by vegetation type (terrestrial biomes) or physical environment (aquatic biomes) Climate is very important in determining why terrestrial biomes are found in certain areas Climate affects the latitudinal patterns of terrestrial biomes © 2014 Pearson Education, Inc. Figure 40.7 30N Tropic of Cancer Equator Tropic of Capricorn 30S Tropical forest Savanna Desert Chaparral Temperate grassland © 2014 Pearson Education, Inc. Temperate broadleaf forest Northern coniferous forest Tundra High mountains Polar ice A climograph plots the temperature and precipitation in a region Biomes are affected not just by average temperature and precipitation, but also by the pattern of temperature and precipitation through the year © 2014 Pearson Education, Inc. Figure 40.8 Annual mean temperature (C) Desert Temperate grassland Tropical forest 30 Temperate broadleaf forest 15 Northern coniferous forest 0 Arctic and alpine tundra 15 0 © 2014 Pearson Education, Inc. 200 100 400 300 Annual mean precipitation (cm) How might catastrophic events affect biomes? © 2014 Pearson Education, Inc. Natural and human-caused disturbances alter the distribution of biomes A disturbance is an event that changes a community by removing organisms and altering resource availability For example, frequent fires kill woody plants preventing woodlands from establishing © 2014 Pearson Education, Inc. General Features of Terrestrial Biomes Terrestrial biomes are often named for major physical or climatic factors and for vegetation Terrestrial biomes usually grade into each other, without sharp boundaries The area of intergradation, called an ecotone, may be wide or narrow © 2014 Pearson Education, Inc. Review the biomes and know the relative latitudinal location, average yearly temperature, average amounts of yearly precipitation, major vegetation in the area and distribution, relative biodiversity. © 2014 Pearson Education, Inc. How might aquatic biomes differ from terrestrial? © 2014 Pearson Education, Inc. Concept 40.2: Aquatic biomes are diverse and dynamic systems that cover most of Earth Aquatic biomes account for the largest part of the biosphere in terms of area They show less latitudinal variation than terrestrial biomes Marine biomes have salt concentrations of about 3% The largest marine biome is made of oceans, which cover about 75% of Earth’s surface and have an enormous impact on the biosphere © 2014 Pearson Education, Inc. Freshwater biomes have salt concentrations of less than 0.1% Freshwater biomes are closely linked to soils and the biotic components of the surrounding terrestrial biome © 2014 Pearson Education, Inc. Describe evolutionary adaptations organisms living in freshwater biomes would have to evolve that organisms in marine biomes would not have to content with. © 2014 Pearson Education, Inc. Aquatic biomes can be characterized by their physical and chemical environment, geological features, photosynthetic organisms, and heterotrophs © 2014 Pearson Education, Inc. Generate a table of the aquatic biomes, be sure to include key characteristics on the physical and chemical environment, geological features, photosynthetic organisms, and heterotrophs for each. Wetlands, Estuaries, Lakes, Streams and Rivers, Intertidal Zone, Coral Reefs, Oceanic Pelagic Zone, Marine Benthic Zone © 2014 Pearson Education, Inc. Zonation in Aquatic Biomes Many aquatic biomes are stratified into zones or layers defined by light penetration, temperature, and depth Review the zonation and describe the factors that determine what organisms will live in different zones. © 2014 Pearson Education, Inc. Describe the biotic factors that will affect the movement of organisms into and out of a particular biome? © 2014 Pearson Education, Inc. Concept 40.3: Interactions between organisms and the environment limit the distribution of species Species distributions are the result of ecological and evolutionary interactions through time Ecological time is the minute-to-minute time frame of interactions between organisms and the environment Evolutionary time spans many generations and captures adaptation through natural selection © 2014 Pearson Education, Inc. Dispersal and Distribution Dispersal is the movement of individuals away from centers of high population density or from their area of origin Why should we care about dispersal patterns? © 2014 Pearson Education, Inc. Transplants indicate if dispersal is a key factor limiting species distributions Transplants include organisms that are intentionally or accidentally relocated from their original distribution If a transplant is successful, it indicates that the species’ potential range is larger than its actual range Species transplants can disrupt the communities or ecosystems to which they have been introduced © 2014 Pearson Education, Inc. Biotic Factors Biotic factors that affect the distribution of organisms may include Predation Herbivory (Interpret the graph, next slide) Mutualism Parasitism Competition © 2014 Pearson Education, Inc. Figure 40.13 Results Seaweed cover (%) 100 80 Both limpets and urchins removed Sea urchin Only urchins removed 60 Limpet 40 Only limpets removed Control (both urchins and limpets present) 20 0 August 1982 © 2014 Pearson Education, Inc. February 1983 August 1983 February 1984 Describe how the following abiotic factors can affect the distribution of biotic factors in a particular biome, with examples. © 2014 Pearson Education, Inc. Abiotic Factors Abiotic factors affecting the distribution of organisms include Temperature Water and oxygen Salinity Sunlight Rocks and soil © 2014 Pearson Education, Inc. Population Ecology Density Distribution Size © 2014 Pearson Education, Inc. Concept 40.4: Dynamic biological processes influence population density, dispersion, and demographics Population ecology explores how biotic and abiotic factors influence density, distribution, and size of populations A population is a group of individuals of a single species living in the same general area Populations are described by their boundaries and size © 2014 Pearson Education, Inc. Density is the result of an interplay between processes that add individuals to a population and those that remove individuals Additions occur through birth and immigration, the influx of new individuals from other areas Removal of individuals occurs through death and emigration, the movement of individuals out of a population © 2014 Pearson Education, Inc. Figure 40.15 (a) Clumped (b) Uniform © 2014 Pearson Education, Inc. (c) Random How is population size controlled? © 2014 Pearson Education, Inc. Concept 40.5: The exponential and logistic models describe the growth of populations Unlimited growth occurs under ideal conditions; in nature, growth is limited by various factors Ecologists study growth in both idealized and realistic conditions © 2014 Pearson Education, Inc. Per Capita Rate of Increase Change in population size can be defined by the equation Change in Immigrants Emigrants population Births entering − Deaths − leaving size population population If immigration and emigration are ignored, a population’s growth rate (per capita increase) equals birth rate minus death rate © 2014 Pearson Education, Inc. The population growth rate can be expressed mathematically as ΔN B −D Δt where N is the change in population size, t is the time interval, B is the number of births, and D is the number of deaths © 2014 Pearson Education, Inc. Births and deaths can be expressed as the average number of births and deaths per individual during the specified time interval B bN D mN where b is the annual per capita birth rate, m (for mortality) is the per capita death rate, and N is population size © 2014 Pearson Education, Inc. The population growth equation can be revised ΔN bN −mN Δt © 2014 Pearson Education, Inc. The per capita rate of increase (r) is given by rb−m Zero population growth (ZPG) occurs when the birth rate equals the death rate (r 0) © 2014 Pearson Education, Inc. Change in population size can now be written as ΔN rN Δt © 2014 Pearson Education, Inc. Instantaneous growth rate can be expressed as dN rinstN dt where rinst is the instantaneous per capita rate of increase © 2014 Pearson Education, Inc. Exponential Growth Exponential population growth is population increase under idealized conditions Under these conditions, the rate of increase is at its maximum, denoted as rmax The equation of exponential population growth is dN rmaxN dt © 2014 Pearson Education, Inc. Exponential population growth results in a J-shaped curve © 2014 Pearson Education, Inc. Figure 40.17 2,000 Population size (N) dN 1.0N dt 1,500 dN 0.5N dt 1,000 500 0 0 © 2014 Pearson Education, Inc. 5 10 Number of generations 15 Why is exponential growth considered to be under ideal conditions. © 2014 Pearson Education, Inc. The J-shaped curve of exponential growth characterizes populations in new environments or rebounding populations For example, the elephant population in Kruger National Park, South Africa, grew exponentially after hunting was banned © 2014 Pearson Education, Inc. Conditions are never ideal. © 2014 Pearson Education, Inc. 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 Carrying capacity varies with the abundance of limiting resources © 2014 Pearson Education, Inc. The Logistic Growth Model In the logistic population growth model, the per capita rate of increase declines as carrying capacity is reached The logistic model starts with the exponential model and adds an expression that reduces per capita rate of increase as N approaches K dN (K −N) rmaxN dt K © 2014 Pearson Education, Inc. Figure 40.19 Exponential growth dN 1.0N dt Population size (N) 2,000 1,500 K 1,500 1,000 Logistic growth (1,500 N) dN 1.0N 1,500 dt Population growth begins slowing here. 500 0 0 © 2014 Pearson Education, Inc. 10 5 Number of generations 15 The Logistic Model and Real Populations The growth of many laboratory populations, including paramecia, fits an S-shaped curve when resources are limited These organisms are grown in a constant environment lacking predators and competitors Animation: Population Ecology © 2014 Pearson Education, Inc. Number of Daphnia/50 mL Number of Paramecium/mL Figure 40.20 1,000 800 600 400 200 0 0 5 10 Time (days) (a) A Paramecium population in the lab © 2014 Pearson Education, Inc. 15 180 150 120 90 60 30 0 0 20 40 60 80 100 120 140 160 Time (days) (b) A Daphnia (water flea) population in the lab Some populations overshoot K before settling down to a relatively stable density Some populations fluctuate greatly and make it difficult to define K © 2014 Pearson Education, Inc. The logistic model fits few real populations but is useful for estimating possible growth Conservation biologists can use the model to estimate the critical size below which populations may become extinct © 2014 Pearson Education, Inc. Population dynamics © 2014 Pearson Education, Inc. Concept 40.6: Population dynamics are influenced strongly by life history traits and population density 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 © 2014 Pearson Education, Inc. “Trade-offs” and Life Histories Organisms have finite resources, which may lead to trade-offs between survival and reproduction Selective pressures influence the trade-off between the number and size of offspring Some plants produce a large number of small seeds, ensuring that at least some of them will grow and eventually reproduce © 2014 Pearson Education, Inc. K-selection, or 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 © 2014 Pearson Education, Inc. How would you differentiate between densityindependent and density-dependent population changes? © 2014 Pearson Education, Inc. 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 © 2014 Pearson Education, Inc. Figure 40.22 Birth or death rate per capita When population density is low, b m. As a result, the population grows until the density reaches Q. When population density is high, m b, and the population shrinks until the density reaches Q. Equilibrium density (Q) Density-independent death rate (m) Density-dependent birth rate (b) Population density © 2014 Pearson Education, Inc. What are some factors that will negatively affect the population size in a density-dependent situation? © 2014 Pearson Education, Inc. Mechanisms of Density-Dependent Population Regulation Density-dependent birth and death rates are an example of negative feedback that regulates population growth Density-dependent birth and death rates are affected by many factors, such as competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factors © 2014 Pearson Education, Inc. Competition for resources occurs in crowded populations; increasing population density intensifies competition for resources and results in a lower birth rate © 2014 Pearson Education, Inc. Toxic wastes produced by a population can accumulate in the environment, contributing to density-dependent regulation of population size © 2014 Pearson Education, Inc. Predation may increase with increasing population size due to predator preference for abundant prey species © 2014 Pearson Education, Inc. Territoriality can limit population density when space becomes a limited resource © 2014 Pearson Education, Inc. Disease transmission rates may increase with increasing population density © 2014 Pearson Education, Inc. Intrinsic factors (for example, physiological factors like hormonal changes) appear to regulate population size © 2014 Pearson Education, Inc.