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Ch.35 Population and Community Ecology

Ch.35 Population and Community Ecology. 35.1 A population is a local group of organisms of one species. Population size depends on… Food Space Weather conditions Breeding patterns Predators Disease. Population Density. Population density = individuals = 1000 trees = 20 trees

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Ch.35 Population and Community Ecology

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  1. Ch.35 Population and Community Ecology

  2. 35.1 A population is a local group of organisms of one species. • Population size depends on… • Food • Space • Weather conditions • Breeding patterns • Predators • Disease

  3. Population Density Population density = individuals = 1000 trees = 20 trees Unit Area 50 km2 km2

  4. Sampling Techniques • Quadrats • Indirect Counting: counting nests or burrows • Mark-Recapture: Individuals are marked/tagged and released. Total Population = (# in 1st capture) (# in 2nd capture) # of marked animals recaptured Count Termite Hills

  5. Limits to Accuracy • Quadrat method assumes organisms are evenly distributed. • The mark-recapture technique assumes marked and unmarked animals have the same chance of being caught.

  6. 35.2 There are limits to population growth. • Population Growth depends on the rate organisms can reproduce. • Exponential Growth: the population multiplies by a constant factor at constant time intervals. • What limits exponential growth?

  7. Carrying Capacity# of organisms in a population that the environment can maintain, or “carry.” • Environmental factors limit growth! • Space • Food • Disease

  8. Factors Affecting Population Growth • Density-Dependent Factors limit a population more as population density increases. • Ex. High-quality food needed to grow and reproduce • Density-Independent Factors don’t depend on population density. • Ex. Weather events, fires

  9. Population Growth Cycles • “boom-and-bust” cycles

  10. 35.3 Biologists are trying to predict the impact of human population growth. History of Population Growth • 1959 – 3 billion • 1999 – 6 billion Factors for Pop. Increase • Farming, not hunting/gathering • Improvements in nutrition, sanitation, and health care • 2050  7.9-10.9 billion!!!

  11. Predicting Future Population Growth

  12. 35.4 Species interact in biological communities. Competition Between Species (Interspecific Competition) • More than 1 species relies on the same resource. Africa Savanna • Community: elephants, gazelles, giraffes, birds, ants, beetles, fungi, bacteria, grasses, trees. • Competition for grass to graze on.

  13. Interspecific Competition… • Competitive Exclusion: when 2 species are so similar in their requirements that the same resource limits both species’ growth and 1 species may succeed over another.

  14. Interspecific Competition… • Niches: Within a community, an organisms habitat, food sources, time of day it’s most active, etc… • What do you think would happen if 2 species had the same exact niche?? feeding niche of the blue-gray gnatcatcher

  15. PredationOne organism eats another organism. • Predator and prey

  16. Predator Adaptations • Speed and agility • Camouflage • Wolves team up in packs. • Rattlesnakes’ heat sensing organs. • Claws, teeth, fangs, stingers… Walking Sticks

  17. Prey Adaptations • Retreat to safe locations, flee from predators • Camouflage • “warning coloration” • Mimicry • Some plants have poisonous chemicals, spines, thorns…

  18. Symbiotic RelationshipsOne species lives on or in another species. • RECAP: endosymbiosis Parasitism • A parasite gets food at the expense of another organism. Mutualism • Both organisms benefit. Commensalism • One organism benefits, the other is unaffected.

  19. 35.5 Disturbances are common in communities. Natural • Fires • Volcanic eruptions • Floods • Storms • Droughts Man-made • Clearing a forest • Ship wrecks Are disturbances always bad??

  20. Ecological SuccessionCommunity change after a disturbance. Primary Succession • Barren ground  community (100s or 1,000s of years! • Ex. New islands formed, land under retreating glaciers Secondary Succession • Disturbance occurs, but soil is left intact. • Ex. Clearing land for farming, then abandoning the land.

  21. Human Activities and Species Diversity  • Clearing Land  species diversity is reduced • Introduced Species are organisms that humans move from their native location to new geographic areas. • Problems???

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