220_Lecture_Population_Ecology_II - I. Population ecology...

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Unformatted text preview: I. Population ecology Population Pop lation = group of i di id l f individuals of the same species living in the same place at the same time What factors affect the number of individuals in one species in one place? age distribution ? rates of birth and death ? population growth ? How Ho do Pop lations G o ? Populations Grow? Three factors that help to predict how population may change Number of individuals already present (N) Population’s carrying capacity (K) Growth rate (r): life-history strategy K & r–Selected Species r– Comparison of Characteristics K-Selected Species Live in stable environment Ecological E l i l specialists i li t Have populations stable in size i Compete well against other species Are restricted in where they can live r-Selected Species Live in disturbed environments Ecological generalists Have populations that fluctuate p p rapidly in size Do not compete well against other species Are widely distributed K & r–Selected Species r– Comparison of Characteristics Are short-lived shortHave many, relatively small young Have short periods of embryonic development Reach adulthood rapidly Invest little or no parental care in young Reproduce once per lifetime K-Selected Species Are long-lived longHave few, relatively large young Have long periods of embryonic development Reach adulthood slowly Invest intensive care in young Reproduce throughout lifetime r-Selected Species S l t dS i Population growth Density – individuals per unit area, this is called crude density ll d d d it Includes: Natality- bi h Natality- birth rate (new births per unit time) li ( bi h i i ) MortalityMortality- death rate (deaths per unit time) Age structure natality related to fertility rate and age structure of population p p mortality related to age-specific survivorship ageand age structure of population Population growth cont’d Crude birth rate = # births/1000 people/yr Crude death rate = # deaths/1000 p p /y people/yr Natural increase of a population = (crude birth rate - crude death rate) (x 100) Zero Population Growth Rate crude birth rate = crude death rate Total G T t l Growth R t th Rate includes immigration and emigration Age Structures St ct es Age pyramids Relative sizes of age groups Judge the status of populations Sex ratios Population Age Structure Pop lation St ct e Age structure diagrams are snapshots of p p populations at particular moment p Expanding population- lots of new births populationStable population- few births populationDiminishing population- natality < populationreplacement l t Fertility Fe tilit Rates Total Fertility Rate = average number of g children a woman will have during her entire reproductive life (based on current ) statistics) ReplacementReplacement-level Fertility rates = average number of children a woman would have for replacement varies between 2 1 and 2 5 2.1 2.5 Environmental conditions restrain perpetual exponential growth l i l h Populations given unlimited resources can g grow exponentially p y Space and resources are not unlimited Eventually, Eventually population densities increase, increase and available resources are spread thin The l i ti Th logistic equation d ti describes changes ib h in population growth rate with increased population size l ti i Logistic Rate of Growth (environmental resistance) carrying capacity (biotic potential) rapid id growth equilibrium Population Regulation Pop lation Reg lation Density dependence Competition – result of limited resources Intraspecific competition – same species Scramble vs contest Exploitation vs interference High density reduces fecundity & increases mortality Plants Not territorial but “claim space” Capture resources Shading Organic toxins The -3/2 power law for plant self-thinning self- Patterns in pop lations Patte ns populations Temporal random periodic Spatial metapopulations & extinction Genetic G ti HardyHardy-Weinberg & deviations Genetic basis for local adaptations Fluctuation is the rule for populations Types of fluctuations Random Coincident with environmental changes Periodic What t pe of patte n is this? type pattern 120 Population size s 100 80 60 40 20 0 0 10 20 30 40 50 Time, years Example of a random fluctuation A non-random fluctuation non- Environmental variability can y affect age structure Periodic fl ct ations Pe iodic fluctuations Can result from time delays in response of population densities Populations can have intrinsic periodicity, like a pendulum The “momentum” can come from high birth rates at low population density Cycles driven by predators are another type, discussed next week 1999 1987 1975 1960 1930 1830 Cultural advances Agricultural advances Industrial and medical advances d Current H man Pop lation C ent Human Population World population size > 6 billion people World Natural rate of increase ~ 1.55 % In one year, (6 billion)(1.55%)=89.9 million added World population doubling time = 45.16 years World A W ld Average Total Fertility Rate=3.0 T t l F tilit R t 3 0 children per woman Is human population growth an p p g environmental problem? Consider the following: • • • • What are our “necessary” resources and do necessary they have unlimited availability? Does earth have a carrying capacity for y g p y humans? How do we value the rights of other g organisms? environmental impact = (#people)(# units of resources per person)(impact per resource unit) In general: gene al fertility rates have declined mortality rates have declined population growth continues because fertility rates still higher than replacement rates (which includes mortality) LDC’s t d t h LDC’ tend to have higher fertility rates hi h f tilit t than MDC’s and higher population growth ...
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