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Transcript
Introduction to Ecology Chapters 52 Figure 50.3 Rachel Carson Ecology • Ecology – the study of interactions between organisms and the environment • Biotic – living components of an ecosystem (ex. animals and plants) • Abiotic - nonliving components of an ecosystem (ex. soil, air, and water) Species distribution • Interactions between organisms and the environment limit the distribution of species. • What affects the distribution of species? – Dispersal limits (range expansions and species transplants) – Behavior and habitat selections – Biotic factors (other species) – Abiotic factors (temperature, water, sunlight, wind, rocks/soil, and climate) Figure 50.7 Spread of the African honeybee in the Americas since 1956 Figure 50.11 Solar radiation and latitude Figure 50.12 What causes the seasons? Figure 50.14 How mountains affect rainfall Figure 50.18 Zonation in a lake Figure 50.22 Zonation in the marine environment Figure 50.24 The distribution of major terrestrial biomes Figure 50.10 A climograph for some major kinds of ecosystems (biomes) in North America POPULATION ECOLOGY CHAPTER 53 POPULATION CHARACTERISTICS • Population – organisms of the same species in the same area • Density – number of individuals in a given area (example: 1200/m2) • Dispersion – pattern of spacing among individuals Measuring Size • Quadrant method used for stationary organisms • Mark and recapture used for mobile organisms Patterns of Dispersion • Clumped – individuals aggregated in patches (most common) • Uniform – evenly spaced individuals • Random – unpredictable, patternless Patterns of dispersion within a population’s geographic range DEMOGRAPHY • Demography is the study of factors that affect populations • Age structure – relative number of individuals of each age • Birthrate or fecundity – number of offspring born during a certain time period • Death rate – number of individuals who die in a certain time period • Generation time – average span between birth of individuals and the birth of their offspring • Sex ratio – proportion of individuals of each sex • Life tables – used to determine how long, on average, an individual of a given age could be expected to live • Cohort – group of individuals of same age • Survivorship curve – a plot of the numbers in a cohort that are alive at each age Life Table for Belding Ground Squirrels (Spermophilus beldini) at Tioga Pass, in the Sierra Nevada Mountains of California Idealized survivorship curves LIFE HISTORIES • Life history – traits that affect an organism’s schedule of reproduction and death • Life histories vary greatly – Salmon travel to ocean to mature and then back to stream to reproduce – Some oaks cannot reproduce until they are at least 20 years old • Semelparity or big bang reproduction – produce numerous offspring and then die • Iteroparity or repeated reproduction – produce fewer offspring over many seasons An example of big-bang reproduction: Agave (century plant) • There is a trade-off between reproduction and survival –Female red deer who are reproductive have a greater chance of dying –Larger brood sizes increase mortality rate Cost of reproduction in female red deer on the Island of Rhum, in Scotland Probability of survival over the following year for European kestrels after raising a modified brood POPULATION GROWTH ΔN = Change in population size B = # births during time interval (birth rate) D = # deaths during time interval (death rate) Δt = time interval ΔN/Δt = B – D Per capita birthrate (b)= # offspring produced per time by an average member of population Ex. 46 births/year in pop of 1000 so b = 46/1000 = 0.046 Birth rate = Expected # births/year for pop (B): B=bN Ex. B = 0.046 x 500 = 23 births/year (where N = 500) Per capita death rate (m)= # deaths per time by an average member of population Ex. 22 deaths/year in pop of 1000 so m = 22/1000 = 0.022 Death rate = Expected # deaths/year for pop (D): D=mN Ex. D = 0.022 x 500 = 11 deaths/year (where N = 500) Maximum per capita growth rate (rmax) ΔN/Δt = bN – mN (birthrate – death rate) r=b–m ΔN/Δt = rmaxN (exponential growth rate) dN/dt = rmaxN (calculus version) • • • • If a population is growing, r is positive. If a population is declining, r is negative. Zero population growth occurs when r = 0 Exponential growth – maximum population growth rate • Intrinsic rate of increase is the maximum population growth rate, rmax • Exponential growth is: • dN/dt = rmax N Population growth predicted by the exponential model Example of exponential population growth in nature • Carrying capacity (K) – maximum population size that a particular environment can support with no net increase or decrease • Logistic Growth – incorporates the effect of population density on rmax, allowing it to vary from rmax under ideal conditions to zero as carrying capacity is reached. • When N is small compared to K, the per capita rate of increase is high. (N = pop size) • When N is large and resources are limiting, the per capita rate of increase is small. • When N = K, pop stops growing. • For logistic growth: ΔN/Δt = rmaxN (K-N/K) Population growth predicted by the logistic model How does the logistic curve fit real populations? • Some populations closely follow the S-shaped curve. • Other populations do not. –Low numbers may hurt a population (rhinos) –Populations may overshoot the carrying capacity and then drop below K. How well do these populations fit the logistic population growth model? Strategies • K-selected populations (density dependent) – organisms that are likely to be living at density near the limit imposed by the environment (K) • r-selected populations (density indepedent) – organisms that are likely to be living in variable environments in which populations fluctuate or in open habitats where individuals are likely to face little competition Characteristics r-selected K-selected Maturation time Short Long Lifespan Short Long Death rate Often high Usually low #offspring/episode Many Few # reproductions/ lifetime Timing 1st reproduction Usually one Often several Early in life Late in life Size of offspring/eggs Small Large Parental care none Often extensive POPULATION LIMITING FACTORS • Limiting factors – factors that limit population growth • Density dependent factors – death rate rises or birth rate falls with increasing pop density • Disease • Predation • Competition • Lack of food • Lack of space • Density independent – birth rate or death rate that does not change with pop density • Climate Decreased survivorship at high population densities Long-term study of the moose (Alces alces) population of Isle Royale, Michigan Extreme population fluctuations Population cycles in the snowshoe hare and lynx Human population growth Demographic transition in Sweden and Mexico, 1750-1997 Age-structure pyramids for the human population of Kenya (growing at 2.1% per year), the United States (growing at 0.6% per year), and Italy (zero growth) for 1995 Annual percent increase in global human pop (data from 2005). Sharp dip in 1960 due mainly to famine in China that killed 60 million people. Infant mortality and life expectancy (from 2005) COMMUNITY ECOLOGY CHAPTER 54 COMMUNITIES • Communities – different populations living within the same area • What factors are most significant in structuring a community? INTERACTIONS • Interspecific interactions – occur between different populations within a community • Coevolution – a change in one species acts as a selective force on another species, and counter-adaptation by the second species, which may cause a selective force on the 1st species. • Predation (+/-) – Lion hunting, killing, and eating a zebra • Parasitism (+/-) – Ticks sucking blood of human • Competition (-/-) – Fighting over resources • Commensalism (+/0) – Birds feeding on insects which bison flush out of grass • Mutualism (+/+) – Legumes with nitrogen fixing bacteria • Herbivory (+/-) – Insects eating plants • Disease (pathogens) (+/-) – Bacteria, viruses, protists, fungi, and prions Figure 53.x2 Parasitic behavior: A female Nasonia vitripennis laying a clutch of eggs into the pupa of a blowfly (Phormia regina) Figure 53.9 Mutualism between acacia trees and ants. The ants live in the hollow thorns and sting other pests. Predation • Cryptic coloration – camouflage • Aposematic coloration – when animals with effective chemical defenses are brightly colored as a warning Figure 53.5 Camouflage: Poor-will (left), lizard (right) Figure 53.6 Aposematic (warning) coloration in a poisonous blue frog Figure 53.x1 Deceptive coloration: moth with "eyeballs" • Mimicry – an organisms mimic another –Batesian mimicry – a harmless species mimics a harmful or unpalatable species –Mullerian mimicry – two or more aposematically species resemble each other Figure 53.7 Batesian mimicry: the hawkmoth larva resembles a snake Figure 53.8 Müllerian mimicry: Cuckoo bee (left), yellow jacket (right) Competition • Competitive exclusion principle – two species with similar needs for the same limiting resources cannot coexist in the same place. –Could lead to extinction of one species • Ecological niche – ecological role; the sum total of the organism’s use of biotic and abiotic resources • Resource partitioning – sympatric (geographically overlapping) species consume slightly different foods or use resources in slightly different ways. • Character displacement – characteristics are more divergent in sympatric populations compared to geographically isolated (allopatric) populations Figure 53.3a Resource partitioning in a group of lizards Figure 53.2 Testing a competitive exclusion hypothesis in the field Figure 53.3bc Anolis distichus (left) perches on sunny areas and Anolis insolitus (right) perches on shady branches. What controls community structure? • • • • • Species diversity Food webs Dominant species Keystone species Foundation species Figure 53.21 Which forest is more diverse? Species Diversity • Species diversity – considers the following: –Species richness – number of different species –Species relative abundance – proportion each species represents of the total individuals in community • Dominant species – most abundant or highest biomass – Ex. American Chestnut was dominant before 1910, but chestnut blight killed all in N. America – Invasive species can become dominant • Keystone species – a predator that makes an unusually strong impact on community structure – Keystone predators maintain higher species diversity by reducing the densities of strong competitors, such that the competitive exclusion of other species does not occur – Ex. Removing Piaster decreased species diversity. Without piaster, mussels overpopulated and excluded other species, Figure 53.14b Testing a keystone predator hypothesis Figure 53.14a Testing a keystone predator hypothesis Figure 53.15 Sea otters as keystone predators in the North Pacific Without sea otters, sea urchins do well and eat kelp. Kelp forests are being destroyed. Otters are being eaten by killer whales. • Foundation species - cause physical changes to environment – Ex. beaver dam, black rush (grass) helps prevent salt build up in soil of marshes Bottom-up or Top-down Controls • Bottom-up = influence from lower to higher trophic levels – Mineral nutrients control the plants, which control the herbivores, which then controls the predators • Top-down = influence from higher to lower trophic levels – Predators limit herbivores, which in turn limits plants, which affects soil nutrients DISTURBANCES • Disturbances are events such as fire, storms, drought, or human activities that damage communities. – Can create opportunities for other species – Human disturbance is not always negative • Yellowstone fire in 1988 killed old forest, but new plants quickly grew in its wake • Dynamic equilibrium hypothesis – species diversity depends on the effect of disturbance on the competitive interactions of populations. Figure 53.16 Routine disturbance in a grassland community Figure 53.18x2 Forest fire SUCCESSION • Ecological succession – transitions in species composition over time • Primary succession – when succession begins in an area that is virtually lifeless and has no soil. • Lichens and mosses are usually the first macroscopic photosynthesizers –Can slowly dissolve rock to make soil, which takes thousands of years Figure 53.18x1 Large-scale disturbance: Mount St. Helens Figure 53.19 A glacial retreat in southeastern Alaska Table 53.2 The Pattern of Succession on Moraines in Glacier Bay • Secondary succession – occurs where an existing community has been cleared by some disturbance that leaves soil intact (example fire or volcanoes erupting) –Typically pioneer species are r-selected (high birthrates and dispersal) Figure 53.18 Patchiness and recovery following a large-scale disturbance ECOSYSTEMS Chapter 55 FOOD WEBS and TROPHIC LEVELS • Autotrophs – Producers make own food • Heterotrophs – Primary consumers = herbivores = eat producers – Secondary consumers = carnivores = eat primary consumers – Tertiary consumers = carnivores = eat secondary consumers – Detritivores (decomposers) = eat detritus (nonliving organic material and dead remains) Figure 54.1 An overview of ecosystem dynamics A Food Web Section 3-2 Figure 54.2 Fungi decomposing a log • Production – rate of incorporation of energy and materials into the bodies of organisms • Consumption – metabolic use • Decomposition – breakdown of organic material into inorganic ENERGY FLOW IN ECOSYSTEMS • Most solar radiation is absorbed, reflected, or scattered in the atmosphere of Earth. • Only a very small portion of sunlight is used by algae, bacteria, and plants for photosynthesis • Primary productivity – amount of light energy converted to chemical energy by autotrophs in an ecosystem in a given time period • Gross primary productivity (GPP) – total primary productivity (not all of this energy is stored in autotrophs because autotrophs use energy for respiration) • Net primary productivity (NPP) NPP = GPP – R Where R = the amount of energy used in respiration Respiration C6H12O6 + 6O2 6CO2 + 6H2O Photosynthesis • Gross primary productivity results from photosynthesis • Net primary productivity is the difference between the yield of photosynthesis and the consumption of fuel in respiration • Primary productivity –J/m2/yr (energy measured per area per unit time) –g/m2/yr (biomass added per area per unit time) • Seasonal changes and available nutrients can limit primary productivity Figure 54.3 Primary production of different ecosystems Figure 54.4 Regional annual net primary production for Earth • Limiting nutrient – the nutrient that must be added to increase primary productivity –Example: nitrogen or phosphorus are often limiting in aquatic systems (especially in the photic zone) • Secondary productivity – rate at which an ecosystem’s consumers convert chemical energy into their own new biomass Figure 54.9 Nutrient addition experiments in a Hudson Bay salt marsh Figure 54.11 An idealized pyramid of net production ECOLOGICAL PYRAMIDS • Pyramid of productivity –~10% rule - ~10% of energy at one level transfers to next level –Where does the energy go? Figure 54.10 Energy partitioning within a link of the food chain • Pyramid of biomass – standing crop biomass (total dry weight) –Some aquatic systems show inverted pyramids because zooplankton consume phytoplankton quickly –Productivity still upright Figure 54.12 Pyramids of biomass (standing crop) Figure 54.13 A pyramid of numbers NUTRIENT CYCLING • Biogeochemical cycles – involve both abiotic and biotic components Figure 54.16 The water cycle Figure 54.17 The carbon cycle CARBON CYCLE • Carbon dioxide in atmosphere is lowest in summer in N. hemisphere and highest in winter. More plants in summer = less CO2 in atmosphere • Dissolved CO2 makes carbonic acid (H2CO3) • Increased burning of fossil fuels has increased CO2 levels, which leads to global warming. –Carbon dioxide absorbs much of the reflected infrared radiation = greenhouse effect. •Without the greenhouse effect, temperature would be –18°C. Figure 54.26 The increase in atmospheric carbon dioxide and average temperatures from 1958 to 2000 (readings taken from Mauna Loa, Hawaii) Global Warming • A number of studies predict CO2 will double by end of 21st century. • Will cause a predicted 2ºC average global temp increase • Historically, a 1.3 ºC would make world warmer than any time in past 100,000 years. • Poles probably most affected and polar ice melting may change our coastlines! Figure 54.18 The nitrogen cycle NITROGEN CYCLE • Plants cannot use N2 (gas). • Nitrogen fixing bacteria convert nitrogen gas into a form of N that plants can use: ammonium (NH4+) or nitrate(NO3-). • Nitrogen fixing bacteria can live in the soil or in plants called legumes (mutualism). • Legumes include beans, alfalfa, and soy. • Denitrifying bacteria convert nitrate back into nitrogen gas. • Without nitrogen fixing bacteria, plants could not get the nitrogen they need and would die. All life on earth depends on these bacteria. Figure 54.19 The phosphorous cycle PHOSPHORUS CYCLE • Phosphorus is often the limiting nutrient in lakes. • Sewage and runoff provide excess phosphorus. This can cause eutrophication. This is when a lake develops a high productivity, which is supported by high rates of nutrient cycling. This leads to algal blooms, which can suffocate the lake. Figure 54.8 The experimental eutrophication of a lake Figure 54.24 We’ve changed our tune BIOLOGICAL MAGNIFICATION • Nonbiodegradable substances become more concentrated in increasing, successive trophic levels. • The biomass at any given level is produced from a much larger biomass ingested from the level below. • Example: DDT caused birds of prey to lay eggs with thin shells. Figure 54.25 Biological magnification of DDT in a food chain Chlorinated Hydrocarbons • Include DDT, agent orange, PCBs (polychlorinated biphenyls) • They are persistent (i.e., they persist in the environment for several years) • They are non-polar (i.e., water-hating) • They bioaccumulate (i.e., they concentrate in the fat of organisms, and their concentration increases as one moves up the food chain) • They are causing a toxic effect at low concentrations • Agent Orange was a defoliant used during the Vietnam War. • Agent Orange is an herbicide that was used during the Vietnam War to strip the land of vegetation making it easier for the US troops to see the opposing forces and also to deplete their food supply. • Dioxin is a very toxic chemical within Agent Orange. • Dioxin is believed to be the cause of so much damage and has been linked to many cancers and birth defects. Dioxin (part of Agent Orange) OZONE DEPLETION • Ozone (O3) provides a protective barrier to UV light. • Chlorofluorcarbons react with O3 and reduce it to O2, which makes holes in the layer. • Largest hole over Antarctica. • Chlorofluorcarbons come from refrigerants, propellants in aerosol cans, and in some manufacturing processes. Figure 54.27a Erosion of Earth’s ozone shield: The ozone hole over the Antarctic Figure 54.27b Erosion of Earth’s ozone shield: Thickness of the ozone layer