Biology 111 Chapter 30 Notes
Biology 111 Chapter 30 Notes BIOL 111
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This 9 page Class Notes was uploaded by Megan Giesler on Wednesday April 20, 2016. The Class Notes belongs to BIOL 111 at University of North Dakota taught by Christopher Felege in Spring 2016. Since its upload, it has received 13 views. For similar materials see Concepts of Biology in Biological Sciences at University of North Dakota.
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Date Created: 04/20/16
Biology 111: Concepts of Biology Chapter 30 30.1 The Scope of Ecology Ecology Scientific study of the interactions of organisms with each other and with their physical environment Offers information key to the survival of all species, present and future Helps us make informed decisions Ecology involves the study of several levels of biological organization o Organisms Focus on adaptations to an environment o Populations Describe changes in population over time o Community All the various populations at a particular locale Study interactions between populations o Ecosystem Living organisms and their physical environment Presence of suspended particles affecting photosynthesis in algae o Biosphere Portion of Earth’s surface where living things exist Understand how various ecosystems contribute to biodiversity and dynamics of biosphere Ecology Began as a part of natural history o Observing and describing organisms in their environment Now an experimental science Central goal to develop models that explain and predict distribution and abundance of populations based on their interactions within an ecosystem Achieving such a goal involves testing hypotheses Ecologists might formulate and test hypotheses about the role fire plays in maintaining a lodge pole pine forest Could compare characteristics of a community before and after a prescribed burn Ecology and environmental science Environmental science o Applies ecological principles to practical human concerns Conservation biology o New discipline that studies all aspects of biodiversity o Goal of conserving natural resources including wildlife for benefit of future generations 30.2 The Human Population Human population has a clumped distribution 56% of the world’s people live in Asia, and most live in China and India Mongolia has a population density of 0.25 persons per square kilometer Bangladesh has a density of over 1,000 person per square kilometer Present population growth Growth of human population has been relatively slow Industrial revolution brought an increase in production of food and jobs Population began to increase steeply Modern medicine increased this growth even further Growth rate of population is the difference between the number of people born and the number of people who die each year o Current global birth rate is 19.14 per 1,000 per year o Current global death rate is 7.99 per 1,000 per year o Current annual growth rate is (19.14 – 7.99)/1,000 = (11.5)/1,000 = 1.11% Future population growth Doubling time for human population is currently 54 years o Doubling time Length of time it takes a population to double in size. Already there are areas across the globe where people have inadequate access to fresh water, food, and shelter o In 54 years, we need to double the amount of food, water, energy, and other resources to maintain the present standard of living Rapid growth usually begins to decline when resources become scarce. o Population levels off at carrying capacity of the environment o Earth’s carrying capacity for humans has not been determined Not all countries have the same growth rate. More-developed versus less-developed countries More-developed countries (MDCs) o North America and Europe o Population growth is modest o People enjoy a fairly good standard of living Less-developed countries (LDCs) o Latin America, Asia, and Africa o Population growth dramatic o Majority of people live in poverty MDCs Did not always have a low growth rate o Between 1850 and 1950 their populations doubled Largely because of decline in death rate o Followed by decline in birth rate o Only modest growth since 1950 Demographic transition o Sequence of events like this decline in death rate followed by decline in birth rate Overall growth rate is 0.2% but some countries are not growing at all or decreasing in size o Higher growth rate of U.S. (0.9%) due to immigration and large number of women of reproductive age LDCs Death rates began to decline rapidly in LDCs after WWII (introduction of modern medicine) Birthrate remained high Collective growth rate of LDCs peaked at 2.5% between 1960 and1965 Rate has declined to 1.5% Growth rates in 46 countries have not declined Population of LDCs is expected to jump to 8 billion by 2050 o The majority of growth will be in Asia o Africa has a high death rate due to AIDS Age structure diagram divided into 3 groups o Prereproductive o Reproductive o Postreproductive Many MDCs have a stable age structure o Number in each category about the same o If replacement reproduction occurs (each couple has 2 children), then population remains the same Most LDCs have a pyramid-shaped age structure o LDC population will continue to expand, even after replacement reproduction attained, as more young women reach reproductive age Population growth and environmental impact Increasing LDC populations might seem to be the main cause of future environmental degradation MDCs, however, consume a much larger percentage of the Earth’s resources o Consumption leads to degradation Environmental impact (E.I.) o Population size x resource consumption per capita o Pollution per unit of resources used Two possible causes of environmental impact o Overpopulation More obvious in LDCs o Resource consumption More obvious in MDCs An average American family is the equivalent of 20 people in India in terms of per capita resource consumption and water requirements MDCs account for only 25% of world population but account for 90% of hazardous waste production 30.3 Characteristics of Populations Various characteristics of populations change over time. Periodically subject to environmental instability Individuals then under the pressure of natural selection Better adapted individuals leave behind more offspring than less adapted individuals Distribution and density Resources o Components of an environment that support its organisms Light, water, space, mates, and food Availability of resources influences the spatial distribution of individuals 3 spatial patterns o Clumped, random, uniform o On a larger scale, members of a population are clumped within a range (portion of globe where species found) because they are areas suitable for their growth Population density o Number of individuals per unit area or volume o Higher in areas with plentiful resources Population growth Growth rate dependent on number of individuals born and number of individuals that die each year Population grows when births exceed deaths Population shrinks when deaths exceed births Demographics Characteristics of a population Availability of resources and demographics influence growth rate of population Age structure Demographic characteristic Births exceed death rate when prereproductive and reproductive individuals outnumber postreproductive If postreproductive individuals exceed the number of reproductive and/or prereproductive individuals, the population will decrease over time o Deaths exceed births A stable population has approximately equal birth and death rates Survivorship How the age at death influences population size Life table o Number of individuals that live or die at each age Dall Sheep example o Constructed using growth rings on horns to estimate time at death Survivorship curve Plots number of survivors per 1,000 births against age Type I o Survival high until old age Type II o Possibility of death equally likely at any age Type III o Death is likely among the young with few individuals reaching old age. Biotic potential Highest potential rate of increase for a population when resources are unlimited Whether potential is high or low depends on demographic characteristics of a population o Availability of resources o Number of offspring per reproduction o Chances for survival until age of reproduction o How often each individual reproduces o Age at which reproduction begins Biotic potential: o Mice—high Produce many offspring that reach maturity quickly o Rhinos—low Only 1 or 2 offspring per infrequent reproductive event Patterns of population growth Dependent on o Biotic potential of species and other demographics o Availability of resources Two fundamental patterns o Exponential growth o Logistic growth Exponential growth J-shaped curve Like compound interest at a bank Phases o Lag phase—growth slow due to few individuals o Exponential growth phase—growth accelerating Can continue only as long as resources are unlimited Competition increases as population approaches number that can be supported by available resources Logistic growth Results in an S-shaped growth curve Phases o Lag phase—growth slow with few individuals o Exponential growth phase—growth accelerating o Deceleration phase—rate of population growth slows due to competition for resources o Stable equilibrium phase—births and deaths about equal Carrying capacity o Total number of individuals that the resources can support Number not constant and varies with circumstances Applications of logistic growth knowledge o If humans using a fish population as a food source want to maintain fish population in exponential growth rate phase Overfishing may push population into lag phase that takes years to recover If people are trying to reduce the number of pests, it is best to reduce carrying capacity rather than reduce population size (encourages exponential growth) Factors that regulate population growth Both biotic (living) and abiotic (nonliving) components regulate population size. Density-independent factors o Abiotic factors, such as weather or natural disasters o Can cause sudden and catastrophic reductions in population size o Cannot in and of itself regulate population size o Intensity of effect does not increase with increased population size Density-dependent factors o Biotic factors Competition, predation, parasitism o Percentage of population affected does increase as population density increases o Intensity of effect increases as density increases Competition o Members of a species compete to utilize resources—light, food, or space—that are in limited supply and necessary for survival o Not all members can have access to a necessary degree o Example Woodpeckers compete for nesting sites Each pair requires a tree hole to raise offspring If there are more holes than pairs, every pair gets a hole If there are fewer holes than pairs, some pairs do not get a hole and do not reproduce Predation - predator eats prey o Lions kill zebras, blue whales strain krill, and deer eat leaves o Effect of predation increases as prey population density increases o Prey easier to find when hiding places are limited o Example Mice must have a hole to hide in to avoid being eaten If there are 102 mice but only 100 holes, 2 mice are in the open—if neither is eaten the predation rate is 0% If there are 200 mice and 100 holes, if only half of the 100 mice without holes are eaten the predation rate is 50/100 or 50% Increasing the density of prey has increased the proportion preyed upon Predator-prey population cycles Some predator and prey populations increase and then decrease in population size. Famous example of snowshoe hare and Canada lynx o Snowshoe hare is an herbivore that feeds on twigs of shrubs and small trees o Assumed lynx decreased hare population o Study found if lynx denied access to hares, cycling of hare population continued based on food availability o Observed pattern based on both hare-food cycle and lynx-hare cycle 30.4 Life History Patterns and Extinction 2 patterns of life history Opportunistic life history pattern o Tends to exhibit exponential growth o Members of population are small in size, mature early, have short life span, and provide limited parental care for a large number of offspring o Tend to be regulated by density-independent effects o Population has high dispersal capacity o Examples—insects and weeds Equilibrium life history pattern o Exhibit logistic population growth o Size of population remains close to or at carrying capacity o Members of the population are large, slow to mature, and have fairly long life spans o Growth regulated by density-dependent effects o Examples—birds and mammals Extinction Total disappearance of a species or higher group Equilibrium species more apt to go extinct o Size of geographic range, degree of habitat tolerance, and size of local population can help determine danger of extinction
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