Population Ecology
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Transcript of Population Ecology
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Population Ecology
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Ecologists study life at many levels, from individual organism to the entire biosphere.
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Ecology: “eco” means house “ology”means study of.
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Levels of organizationCells – Tissue-Organs – Organ systems -Organisms
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Population – a group of individuals of the same species that live in the same area at a given time
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Example: a group of white-tailed deer in an oak-hickory forest in southeastern PA
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Community - groups of living organisms that interact with one another in a particular area.
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Example: deer, mice, bushes and snakes in the forest community
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Ecosystem: a community together with its physical environment
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Biosphere: all parts of the earth that hosts life, with all of its organisms and environments.
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Ecosystems include both biotic and abiotic factors. Biotic factors are parts of the ecosystem that are living.
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Abiotic factors are parts of the ecosystem that are non-living.
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Biotic factors:
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Abiotic:
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Organisms depend on resources provided by their habitat for survival.
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The specific environment in which an organism lives is its habitat.
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A habitat provides an organism with resources. A resource is anything an organism needs to survive.
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Describing Populations….
The OVERALL health of a population can often be monitored by tracking how its size changes.
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Population size describes the number of individual organisms present in a given population at a given time.
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Population EcologyDeals with the # of individuals of a particular species that are found in an area and how and why those numbers change or remain fixed over time.
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Population ecologists study…
How populations respond to its environment
Competition for resources, predations, disease and other environmental pressures
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Determine population size by sampling. Instead of counting every individual, ecologists count every organism in a small area than estimate the number of individuals in the larger area.
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Population density describes the number of individuals within a population per unit area.
For example: 1500 golden toads per 4 sq. kilometers
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In general, larger animals have lower population density because they need more resources.
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High population density can make it easier to find mates and group together. However, it also leads to more competition for resources.
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Overcrowded organisms can also lead to increase of disease and vulnerable to predators.
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Age structure diagrams show the number of males & females in different age groups within a population.
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Age structure describes the relative number of organisms of each age with in a population.
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Age structure diagrams are a visual tool to show the age structure of populations.
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Stable – approximately the same number of individuals at each age grouping, mix of young and old
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Growing – mostly young
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Declining – the largest portion of population is older
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A population’s growth rate is determined by births, deaths, immigration and emigration.
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All things being equal, when a population birthrate is greater than its death rate, population size will increase.
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When death rate is greater than its birth rate, population size will decrease.
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In addition to births & deaths, population size can also change by individuals moving in & out.
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Immigration – movement of individuals into a populationEmigration – movement of individuals into a population
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Birthrate – number of live births per 1000 in a given yearDeath rate – number of deaths per 1000 in a given year
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CALCULATING GROWTH RATE
Growth rate (r) = birth rate (b)+ I – death rate (d) + E
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Population growth is typically reported as a net change per 1000 individuals.
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Exponential growth is when a population increases by a fixed percentage each year.
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Exponential growth occurs in nature only when the starting population is small & the environmental conditions are ideal.
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This type of growth usually does not last long. Most populations are constrained by limiting factors.
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Limiting factors are characteristics of the environment that limit population growth. Limiting factors determine a population’s carrying capacity.
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Example: New population is introduced…mold growing on bread.
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Logistic Growth describes how a population’s initial exponential increase is slowed & finally stopped by limiting factors.
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Carrying capacities are not fixed. Carrying capacity is the largest population size a given environments can sustainably support.
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Examples of limiting factors:
1) Food 2) Disease3) Predators4) Space5) Water
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Limiting factors have more of an effect in dense populations & other limiting factors affect all populations in the same way.
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Density–DEPENDENT factor:
factors that limits the population size or density
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Disease (example: HIV)CompetitionPredatorsParasitesFood
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Density INDEPENDENT factor: affect ALL populations, regardless of size of the population
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TemperatureStormsFloodsDroughtVolcanic eruption
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Biotic potential is the maximum ability to produce offspring in ideal conditions.
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Biotic potential is based on…
• Age at which reproduction takes place
• % of life span that an organism can reproduce
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• Number of offspring in each reproduction period
• Generally larger animals have a lower biotic potential than microscope organisms.
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Rapid life history (example: mosquitoes)
Rapid reproductionHigh number of offspringSmall body size
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Small body sizeOrganisms mature rapidlyReproduce earlyOrganisms have a short life span
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Slow life history (example: elephant)
Slow reproductionLow number of offspringLarge body size
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Organisms mature slowlyReproduce lateOrganisms have a long life spanOrganisms tend to have parental care