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Understanding Population and Community Ecology

Learn about population dynamics, limits to growth, species interactions, and the impact of human population growth on ecosystems. Discover how disturbances and ecological succession shape biological communities. Explore interspecific competition, predation, symbiotic relationships, and the consequences of human activities on species diversity.

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Understanding 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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