2Ostriches are nomadic, wandering in small groups. PopulationsPopulation: a group of organisms of the same species that live within a given areaKey characteristics:Growth RatePopulation densityDispersal PatternsLife-History PatternsOstriches are nomadic, wandering in small groups.PopulationsA population is a group of individuals of the same species living within a designated area at one time. The boundary of the population may be physical—such as a mountain range—or defined by a scientist for purposes of study.Demography is the statistical study of populations. Three important aspects of population structure are: dispersion patterns or spacing, population density, and growth rate.ReferencesCampbell, N.E. & Reece, J.B. (2002). Biology, (6th ed.). San Francisco: Benjamin Cummings.Image ReferenceNOVA Development Corp. (1995) Birds #2289. Art Explosion, Volume 2 Clip ArtNOVA Development Corp. (1995) New England #57. Art Explosion, Volume 2 Clip ArtAspen trees are quick to pioneer areas that have been disturbed by fire.
3PopulationsPopulations—large and small—are DYNAMICMeaning, they change over timeHumans face the same problems as large and small populations in nature
9 Self Check A. population increases exponentially Characteristics of Population GrowthExponential growthJ curveS curvePopulationTimeCarrying capacity Self Check Which of the following would you expect to observe after a population exceeds its carrying capacity?A. population increases exponentiallyB. births exceed deathsC. deaths exceed birthsD. population growth rate is unaffected by limiting factorsThe answer is C.
10Population Size Perils of Small Populations low genetic diversitysubject to inbreedingless likely to adapt to environmental changesProblems being a Large populationIncrease food shortages & diseasesDecrease in space, clean waterLive at carrying capacity so can experience huge crash
11Factors That Influence Population Size Population growth rate is determined by:Natality or Birth rateDeath rateIt is also influenced by the number of individuals that enter and leave a population.Immigration – move into populationEmigration – move out of population
12Limits on Population Growth Limiting Factors- any factor that causes a population to decreaseDensity Dependent Limiting FactorsDepends on the size of the populationEx. Food, Water, Shelter, Disease, CompetitionDensity Independent Limiting FactorsCan affect populations regardless of their densityEx. Weather, ClimateFloods, Drought, Tornadoes, Fire, VolcanoesWater and shelter arecritical limiting factors inthe desert.Limits on Population GrowthCarrying capacity (K) is the maximum number of organisms of a population that can be supported by a particular habitat. As population numbers approach the carrying capacity of an environment, in other words as density increases, competition for resources is amplified. Density-dependent factors in an environment include available food, nutrients in the soil, water, and shelter, among many others. The buildup of metabolic wastes also increases with density and adversely affects many populations as well.Weather, climate, and human activities can be density-independent factors which affect the environment. In the case of catastrophic events or the pressure of toxins, populations are affected regardless of size. Populations recover at different rates, some even experiencing a permanent decline after a major change in the environment.ReferencesCampbell, N. E. & Reece, J. B. (2002). Biology (6th ed.). San Francisco: Benjamin Cummings.Raven, P. H. & Johnson, G. B. (2002). Biology (6th ed.). McGraw-Hill.Image ReferenceNOVA Development Corp. (1995) Birds #2516. Art Explosion, Volume 2 Clip ArtNOVA Development Corp. (1995) Wilderness #319. Art Explosion, Volume 2 Clip ArtFire is an example of aDensity independentLimiting factor.
15Predator & PreyPredator: Organism that eats all or part of another organismPrey: an organism that gets eaten by another organism
16Competition: two or more organisms using the same resources Between different species and the same species
17Population DensityPopulation density is total population size per unit of area.Population densities depend on:Interactions within the environmentQuality of habitatDensity dependent factorsDensity independent factorsBirth rate and death ratePopulation DensityPopulation density is a measure of the number of individuals of the same species living in a designated unit of space. It is influenced by relationships among organisms, movement of individuals in and out of the habitat, resources, and abiotic environmental factors (such as climate). Fluctuations in population density can be indications of changes in the environment.Carrying capacity is the maximum number of organisms in a population that can be supported by a particular habitat. Many factors determine carrying capacity, some of which are influenced by the density of the population, while others are not. Density-dependent factors in an environment might be influenced by available food, water, and shelter. Density-independent factors include all facets of weather and climate, such as droughts, storms, and volcanic eruptions.It often is difficult to determine the size of a population because of the wide range of the habitat or mobility of the organisms. In such cases, ecologists use a variety of sampling methods. For instance, a designated area of study might be sectioned into grids or plots. Numbers of organisms counted in selected grids are extrapolated to estimate the total population size. Mark-and-recapture is another method used to estimate population size in large geographic areas. Traps are set in the study area. Trapped organisms are tagged and released. After a period of time, traps are set again, and calculations are made based on the number of marked organisms that are recaptured.Total population = total size of 2nd sample X marked # in 1st catchmarked # recaptured in 2nd catchReferences:Campbell, N. E. & Reece, J. B. (2002). Biology (6th ed.). San Francisco: Benjamin Cummings.Ricklefs, R. E. & G. L. Miller. (2000). Ecology (4th ed.). New York: W.H. Freeman and Co.
18Dispersal Patterns Within Populations Three common patterns of distribution are:Dispersion Patterns Within PopulationsThe arrangement, or dispersion, of individuals in relation to one another within a given area is one key characteristic of population study, as it reflects interactions among the population and the environment. Three patterns of population dispersion are clumped, evenly spaced, and random.The most frequent pattern of distribution in a population is clumped. Individuals are clustered together in groups in response to uneven distribution of resources, tendency of offspring to remain with parents, or some type of social order. Clumping also may be linked with defense (safety in numbers) or mating behavior. In plants, soil type, availability of water or the manner in which the plant reproduces may favor clumped distribution patterns.Evenly spaced distributions, in which members of the population maintain a minimum distance from one another, generally indicates strong intraspecific competition. In plant populations, this could result from competition for water, sunlight, or available nutrients, while among animals, even spacing indicates strong territoriality.Random spacing is the least common pattern of distribution found in populations. It usually occurs because members of a species do not frequently interact with one another or are not heavily influenced by the microenvironments within their habitat.ReferencesCampbell, N. E. & Reece, J. B. (2002). Biology (6th ed.). San Francisco: Benjamin Cummings.Raven, P. H. & Johnson, G. B. (2002). Biology (6th ed.). McGraw-Hill.Image ReferenceYoung, M. (2004). Dispersion patterns within populations. Houston, TX: Baylor College of Medicine, Center For Educational Outreach.
20When Studying Populations… The best way to determine population size is to collect an absolute number.Count up all the individuals in the population.More frequently used is population density.The number of individuals per unit area.Can be measured using a variety of sampling techniques.
21Random SamplingA method of selecting a sample from a statistical population in such a way that every possible sample that could be selected has a predetermined probability of being selected (random sample).BEST FOR:Stationary PopulationsEx. PlantsEven Dispersal Patterns
22mathematical formula estimates the pop size Mark and RecaptureA method of sampling an animal population where animals are caught alive and tagged, and then returned (unharmed) to their habitatover time animals from the pop are trapped and those with marks/tags are countedmathematical formula estimates the pop size
23Patterns in Populations Reproductive pattern = life-history patternVariety of patterns, but TWO extremes
24Patterns Rapid life-history patterns Changing or unpredictable environmentSmallMature rapidlyReproduce earlyShort life span
25Patterns Slow life-history pattern Large species Stable environments Reproduce slowlyMatures slowlyLong life spanStay at or near carrying capacity
26Reproductive Strategies Rapid (maximum growth rate, below carrying capacity)Early reproductionShort life spanHigh mortality rateLittle or no parental careLarge investment in producing large numbers of offspringBelow carrying capacityExamples:Bony fishGrasshoppersSlow (maximizes population size near carrying capacity)Late reproductionLong life spanLow mortality rateExtensive parental careGreater investment in maintenance and survival of adultsAt or near carrying capacityExamples:SharksElephantsReproductive StrategiesIn an uncrowded environment, such as a recently abandoned crop field, natural selection pressure tends to favor populations that invest heavily in offspring, have shorter life spans, capacity for widespread dispersion, and usually provide little or no parental care for offspring (for example, mosquitoes, ragweed, or mice). These populations tend to increase exponentially and often are referred to as r-strategist, where r refers to the intrinsic rate of growth of the population. In contrast, crowed conditions favor organisms with lower rates of population growth, but improved capabilities to utilize and compete for resources. These populations maintain themselves at levels close to carrying capacity (K) and are referred to as K-strategist.Biologist refer to the types of selection pressure placed on populations as r-selection, if individuals that reproduce rapidly and abundantly are favored, and as K-selection, if individuals that compete well in crowded conditions are favored over time.ReferencesCampbell, N. E. & Reece, J. B. (2002). Biology (6th ed.). San Francisco: Benjamin Cummings.Odum, E. (1997). Ecology: A Bridge Between Science and Society. Sunderland, MA: Sinauer Associates, Inc.Raven, P. H. & Johnson, G. B. (2002). Biology (6th ed.). McGraw-Hill.
27Survivorship in Populations Survivorship curves are graphic representations of the age structure of a given population. They are used to predict the future growth of the population. Type I curves reflect relatively low death rates early in life and through midlife, with a sharp increase in death rate among older-age groups (e.g., humans). Type II curves illustrate a fairly even mortality rate throughout the life span of the organism (e.g., birds). Populations with high death rates early in life followed by a sharp decline of death rates for the survivors are represented by Type III survivorship curves (e.g., fish and many insect populations).ReferencesCampbell, N. E. & Reece, J. B. (2002). Biology (6th ed.). San Francisco: Benjamin Cummings.Ricklefs, R. E. & G. L. Miller. (2000). Ecology (4th ed.). New York: W.H. Freeman and Co.Image ReferenceYoung, M. (2004). Survivorship graph. Houston, TX: Baylor College of Medicine, Center For Educational Outreach.
28Survivorship Curves Patterns of Mortality Populations show three patterns of mortality or survivorship curves:Type I (low mortality until late in life)Type II (constant mortality throughout life)Type III (high mortality early in life followed by low mortality for the remaining life span)
29Survivorship in Populations Survivorship curves are graphic representations of the age structure of a given population. They are used to predict the future growth of the population. Type I curves reflect relatively low death rates early in life and through midlife, with a sharp increase in death rate among older-age groups (e.g., humans). Type II curves illustrate a fairly even mortality rate throughout the life span of the organism (e.g., birds). Populations with high death rates early in life followed by a sharp decline of death rates for the survivors are represented by Type III survivorship curves (e.g., fish and many insect populations).ReferencesCampbell, N. E. & Reece, J. B. (2002). Biology (6th ed.). San Francisco: Benjamin Cummings.Ricklefs, R. E. & G. L. Miller. (2000). Ecology (4th ed.). New York: W.H. Freeman and Co.Image ReferenceYoung, M. (2004). Survivorship graph. Houston, TX: Baylor College of Medicine, Center For Educational Outreach.
30Rapid Life History Pattern Type III Survivorship Type III Species:have high reproductive ratestend to occur in unpredictable environmentsEx. Fish, Plantsr-selected Reproductive StrategyFor r-selected species, “r” refers to the growth rate term in the logistic population growth model. For these species, population sizes and mortality tend to be variable and unpredictable. Since populations frequently are far from carrying capacity (“K”), intraspecific competition often is weak. Selection tends to favor individuals with rapid development, high and early reproduction that is not repeated, small body sizes, high resource requirements, and short lives. The potential for populations of r-selected species to grow is large.Reference:Pianka, E. (1970). On r- and K selection. American Naturalist, 104,Image Reference:Baylor College of Medicine, Center For Educational Outreach. (2004). Martha Young, Senior Graphic Designer
31Slow Life History Pattern Type I Survivorship Type I Species:occur near carrying capacityexperience effects of population densityhave low reproductive rates, high parental careEx. Humans, ElephantsK-selected Reproductive StrategyIn contrast, k-selected species have more constant mortality and population sizes that often are close to carrying capacity. Intraspecific competition tends to be strong. Selection favors slower development, late, repeated reproduction, long lives, and efficient use of resources.Reference:Pianka, E. (1970). On r- and K selection. American Naturalist, 104,Image Reference:Baylor College of Medicine, Center For Educational Outreach. (2004). Martha Young, Senior Graphic Designer
32Age Structures and Human Growth Human PopulationsAge StructuresandHuman Growth
33Age StructureA population’s age structure indicates the percentage of individuals at each age.The right side shows females; the left, malesThe x-axis is number is populations sizeUsually in millionsThe y-axis is age ranges usually 0-4, 5-9, 10-14, etc…
34Population Age Structure Differences in environmental conditions and past history may cause populations to differ in their age distributions.The future growth of a population depends on its current age distribution.Population Age StructureDifferences in environmental conditions and past history may cause populations to differ in their age distributions. The future growth of a population will depend on its current age distribution if birth and death rates vary with age.Reference:Ricklefs, R.E. & Miller, G.L. (2000). Ecology ,(4th ed.). NY: WH Freeman and Co.U.S. Census Bureau. (2003). International Data Base. Retrieved fromImage Reference:Baylor College of Medicine, Center For Educational Outreach. (2004). Martha Young, Senior Graphic Designer.
39History of Human Population Growth The Development of AgricultureAbout 10,000 to 12,000 years ago, the development of agriculture increased the growth rate of the human population.
40What happened in the 1600s? The Population Explosion Around 1650, improvements in hygiene, diet, and economic conditions further accelerated population growth.After World War II, the human population grew at the fastest rate in history, largely because of better sanitation and medical care in poorer countries.
43Human Population Growth Human population growth rate has been growing more than exponentially.Limited resources eventually will cause human population growth to slow, but global human carrying capacity is not known.
441. What is the difference between linear growth and exponential growth as plotted on a graph?
452. Why don’t populations of organisms grow indefinitely. 3 2. Why don’t populations of organisms grow indefinitely? 3. What is the relation ship of births to deaths in a population before the population reaches the environment’s carrying capacity? 4. What happens when the population exceeds the carrying capacity? 5. What are some limiting factors that can curb population growth?