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21-ch36-populations - Chapter 36 Chapter 36 Population...

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Unformatted text preview: Chapter 36 Chapter 36 Population Dynamics wildlife day shifts Population Population ecology is the study of how & why populations change population ecology – study of changes in population size & factors that regulate populations over time population – group of individuals of a single species living in the same place; interbreeding density – number of individuals per unit area (or volume) dispersion – pattern of spacing among individuals of spacing among individuals clumped uniform Population Population Size immigration – add new individuals from other populations emigration – movement of individuals out of population population size is determined by: birth + immigration death + emigration Models of population growth tend to Models of population growth tend to assume assume immigration = emigration (focus on births & deaths instead) Demography: Demography: vital statistics of populations changing over time life tables – age specific summaries of survival pattern in population cohort – group of individuals of the same age; follow fate from birth to death survivorship curve – plot of proportion in cohort cohort still alive at each age Type I curve – low death rates in early & middle life; increase in older age groups iddl lif Type II curve – death rate constant for all age groups why? age groups... why? Type III curve – high death rates highest for young age groups... why? for young age groups why? Idealized Idealized models help us understand population growth exponential growth – geometric increase in unlimited conditions whole population multiplies by constant factor (each time interval) 2, 4, 8,16, 32, 64, etc. does exponential growth happen in nature? under what conditions? what conditions? The The exponential model represents population growth in an idealized environment with unlimited resources exponential growth may be sustained for a limited time interval in nature, exponential growth happens only when populations are small populations are small compared compared to resources (in absence of strong influence of predators, disease, etc.) The The logistic growth model includes the concept of carrying capacity limiting factors – environmental factors that restrict pop. growth carrying capacity – max. pop. size that environment can support - defined for given organism, habitat; varies with resources - consider food, water, sunlight, refuges, nesting sites, etc. The The logistic growth model includes the concept of carrying capacity logistic population growth – population population growth growth slowed by limiting factors as size increases; approaching carrying capacity why does growth rate slow? two possible options... influenced by many factors Populations are regulated by complex interactions density density-dependent (birth or death rate) – reproductive output (birth or death rate) output changes with population density (i.e., inverse relationship) many possible consequences of crowding higher death rate - intense competition for resources exploitative vs. interference vs interference - health (malnutrition, epidemics, etc.) - increased predation (& cannibalism) - toxic waste build-up waste build lower birth rate - intrinsic factors (social, hormonal, etc.) Parasitic roundworms slow their reproductive rate reproductive rate when the intestine is full of them. Organisms with a history of overcrowding are more likely to di lik exhibit adaptations like densitydensitydependent fecundity. population cycle (rare event) – regular fluctuations; “boom & bust” unusually long-term data set long(pelts sold by trappers) which animal drives the cycle? (both!) animal drives the cycle? (both!) hare population limited by predation lynx population limited by food supply trade offs: when time, energy, nutrients are used for one thing they cannot be used for another how often can broods be produced without compromising future success? how many per brood vs. how much investment Lower survival rates of kestrels with larger broods indicate that caring larger broods indicate that caring for for more offspring negatively affects survival of the parents. Principles of population ecology have practical applications sustainable resource management sustainable resource management – harvesting without without damaging the resource maximum sustained yield – harvesting at a level that produces sustained yield at level that produces a constant yield without forcing a population into decline Newfoundland cod fishery collapse (one of many historical examples of unsustainable harvest) unsustainable harvest) http://www.msc.org/about-us/vision-mission http://www.msc.org Economic Economic fisheries that have already collapsed… Grand Banks cod (Canada) Atlantic swordfish Murray River cod (Australia) Atlantic halibut halibut Atlantic bluefin tuna Argentinean hake Principles of population ecology have practical applications Integrated Pest Management Integrated Pest Management – use of ecological knowledge & of ecological knowledge principles to control unwanted species • agricultural pests pests • threats to public health • invasive & feral species eradication is not a realistic goal... http://www.nysaes.cornell.edu/ent/biocontrol/ http://www.epa.gov/opp00001/factsheets/ipm.htm http://ars.usda.gov/Research/Research.htm?modecode=53-47-10-05 Consider Consider human population growth age structure – relative number of individuals of each age group structure number of individuals of each age group predict relative population dynamics for each pattern below... There There are two ways to reach r = 0 Zero Population Growth (ZPG) 1) ZPG = high birth rate - high death rate or 2) ZPG = low birth rate - low death rate demographic transition – movement from first scenario (above) to second scenario; during this time growth rate (r) is positive When When girls go to school, population growth tends to decline. http://www.un.org What What happened to the… • Vikings who colonized Greenland? • Pueblo astronomers of Chaco Canyon? • great ancient Mayan civilization? What caused the… • genocide in Rwanda? • economic devastation of Haiti? What can we learn from past mistakes? http://www.npr.org/templates/player/mediaPlayer.html?action=1&t=1&islist=false&id=4276179&m=4276180 http://www.ted.com/talks/lang/eng/jared_diamond_on_why_societies_collapse.html w t / n o p • stone carvers of Easter Island? Carrying Carrying capacity on a global scale ecological footprint – aggregate land & water used for a nation, state, city, individual, etc. - crop lands, pasture, forest, ocean, urbanization, fossil energy ecological capacity – actual resource base of each nation consider sustainability what factors will limit human population growth? - food? - nonrenewable resources? - epidemics? - voluntary reduction: reduction: * offspring production * resource use please do try this at home! http://www.footprintnetwork.org/en/index.php/GFN/page/calculators/ Developing countries may have higher birth rates, but take hi bi a look at our resource use! ...
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