Populations and communities

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  • The J–shaped curve of exponential growth is characteristic of some populations that are introduced into a new or unfilled environment or whose numbers have been drastically reduced by a catastrophic event and are rebounding. The graph illustrates the exponential population growth that occurred in the population of elephants in Kruger National Park, South Africa, after they were protected from hunting. After approximately 60 years of exponential growth, the large number of elephants had caused enough damage to the park vegetation that a collapse in the elephant food supply was likely, leading to an end to population growth through starvation. To protect other species and the park ecosystem before that happened, park managers began limiting the elephant population by using birth control and exporting elephants to other countries.
  • The population doubled to 1 billion within the next two centuries, doubled again to 2 billion between 1850 and 1930, and doubled still again by 1975 to more than 4 billion. The global population now numbers over 6 billion people and is increasing by about 73 million each year. The population grows by approximately 201,000 people each day, the equivalent of adding a city the size of Amarillo, Texas, or Madison, Wisconsin. Every week the population increases by the size of San Antonio, Milwaukee, or Indianapolis. It takes only four years for world population growth to add the equivalent of another United States. Population ecologists predict a population of 7.3–8.4 billion people on Earth by the year 2025.
  • We consume more than just food: water, energy, space/habitat
  • The population doubled to 1 billion within the next two centuries, doubled again to 2 billion between 1850 and 1930, and doubled still again by 1975 to more than 4 billion. The global population now numbers over 6 billion people and is increasing by about 73 million each year. The population grows by approximately 201,000 people each day, the equivalent of adding a city the size of Amarillo, Texas, or Madison, Wisconsin. Every week the population increases by the size of San Antonio, Milwaukee, or Indianapolis. It takes only four years for world population growth to add the equivalent of another United States. Population ecologists predict a population of 7.3–8.4 billion people on Earth by the year 2025.
  • We consume more than just food: water, energy, space/habitat
  • Populations and communities

    1. 1. Population Ecology 2005-2006
    2. 2. Changes topopulation size• Adding & removing individuals from a population • birth • death • immigration • emigration 2005-2006
    3. 3. Growth rate • Exponential growth • characteristic of a population without limiting factors • ex. introduced to a new environmentWhooping crane African elephantcoming back from near extinction protected from hunting 2005-2006
    4. 4. Carrying capacity• Can populations continue to grow exponentially? • of course NOT! • what sets limit? • resources, predators, parasites• Carrying Capacity (K) • maximum population size that environment can support with no degradation of habitat • not fixed; varies with changes in resources 2005-2006
    5. 5. Model of growth Decrease in rate of growth as reach carrying capacity 2005-2006
    6. 6. Different life strategies • K-selection • r-selection K-selection mortality constant r-selection 2005-2006
    7. 7. Reproductive strategies• K-strategy • have few offspring & invest a lot of energy in raising them to reproductive age • primates • coconut• r-strategy • have many offspring & invest little in their survival • insects • dandelion & other weeds 2005-2006
    8. 8. Predator – prey interactions • Population cycles 2005-2006
    9. 9. Age structure • Relative number of individuals of each age What do the data imply about population growth in these countries? 2005-2006
    10. 10. Human populationWhat factors have contributed to this exponentialgrowth pattern? 2005→6 billion Is the human population reaching carrying capacity? 1650→500 million 2005-2006
    11. 11. Community Ecology2005-2006
    12. 12. Inter-species interactions • Symbiotic interactions • competition (-/-) • compete for limited resource • 2 species cannot coexist in a community if their niches are identical • predation / parasitism (-/+) • mutualism(+/+) • lichens (algae & fungus) • commensalism (+/0) • barnacles attached to whale 2005-2006
    13. 13. (+/+) mutualismcommensalism (+/0) (-/-)predation (+/-) competition 2005-2006
    14. 14. Niche • An organism’s niche is its ecological role habitat = address, niche = job Resource partitioning 2005-2006
    15. 15. Niche & competition • Competitive Exclusion • No two similar species can occupy the same niche at the same time 2005-2006
    16. 16. Predation drives evolution • Predators adaptations • locate & subdue prey • Prey adaptations • elude & defendhorns, speed, coloration spines, thorns, toxins 2005-2006
    17. 17. Trophic structure • Food chains • feeding relationships • food chain usually 4 or 5 links = trophic levels • length of food chain limited by inefficiency of energy transfer 2005-2006
    18. 18. Energy transfer• Energy in • from the Sun • captured by autotrophs = producers (plants)• Energy through • food chain • transfer of energy from autotrophs to heterotrophs (herbivores to carnivores) • heterotrophs = consumers • herbivores • carnivores 2005-2006
    19. 19. Energy inefficiencyincomplete metabolismdigestion 2005-2006
    20. 20. Pyramids of production • represent the loss of energy from a food chain • how much energy is turned into biomass 2005-2006
    21. 21. Food webs • Food chains are hooked together into food webs • Who eats whom? • a species may weave into web at more than 1 trophic level • bears • “there’s always a bigger fish”What limits the length ofa food chain? 2005-2006
    22. 22. Implications • Dynamics of energy through ecosystems have important implications for human populations • what food would be more ecologically sound? 2005-2006
    23. 23. Disturbances • Most communities are in a state of change due to disturbances • fire, weather, human activities, etc. • not all are negative 2005-2006
    24. 24. Disturbances • Disturbances are often necessary for community development & survival 2005-2006
    25. 25. Different life strategies • K-selection • r-selection K-selection mortality constant r-selection 2005-2006
    26. 26. Reproductive strategies • K-strategy • have few offspring & invest a lot of energy in raising them to reproductive age • primates • coconut • r-strategy • have many offspring & invest little in their survival • insects • dandelion & other weeds 2005-2006
    27. 27. Predator – prey interactions • Population cycles 2005-2006
    28. 28. Age structure • Relative number of individuals of each age What do the data imply about population growth in these countries? 2005-2006
    29. 29. Human population 2005→6 billion What factors have contributed to this exponential growth pattern? Is the human population reaching carrying capacity? 1650→500 million 2005-2006
    30. 30. Community Ecology2005-2006
    31. 31. Inter-species interactions • Symbiotic interactions • competition (-/-) • compete for limited resource • 2 species cannot coexist in a community if their niches are identical • predation / parasitism (-/+) • mutualism(+/+) • lichens (algae & fungus) • commensalism (+/0) • barnacles attached to whale 2005-2006
    32. 32. (+/+) mutualismcommensalism (+/0) (-/-)predation (+/-) competition 2005-2006
    33. 33. Niche • An organism’s niche is its ecological role habitat = address, niche = job Resource partitioning 2005-2006
    34. 34. Niche & competition • Competitive Exclusion • No two similar species can occupy the same niche at the same time 2005-2006
    35. 35. Predation drives evolution • Predators adaptations • locate & subdue prey • Prey adaptations • elude & defendhorns, speed, coloration spines, thorns, toxins 2005-2006
    36. 36. Trophic structure• Food chains • feeding relationships • food chain usually 4 or 5 links = trophic levels • length of food chain limited by inefficiency of energy transfer 2005-2006
    37. 37. Energy transfer• Energy in • from the Sun • captured by autotrophs = producers (plants)• Energy through • food chain • transfer of energy from autotrophs to heterotrophs (herbivores to carnivores) • heterotrophs = consumers • herbivores • carnivores 2005-2006
    38. 38. Energy inefficiencyincomplete metabolismdigestion 2005-2006
    39. 39. Pyramids of production • represent the loss of energy from a food chain • how much energy is turned into biomass 2005-2006
    40. 40. Food webs• Food chains are hooked together into food webs• Who eats whom? • a species may weave into web at more than 1 trophic level • bears • “there’s always a bigger fish”What limits the length ofa food chain? 2005-2006
    41. 41. Implications • Dynamics of energy through ecosystems have important implications for human populations • what food would be more ecologically sound? 2005-2006
    42. 42. Disturbances • Most communities are in a state of change due to disturbances • fire, weather, human activities, etc. • not all are negative 2005-2006
    43. 43. Disturbances • Disturbances are often necessary for community development & survival 2005-2006
    44. 44. Ecological cycle fire as part of a natural community cycle 2005-2006
    45. 45. Ecological succession • The sequence of community changes after a disturbance • transition in species composition over ecological time • years or decadesMt. St. Helens 2005-2006
    46. 46. Successionover time Change in species mix • From bare soil, then… { • bacteriamakesoil • lichens & mosses • grasses • shrubs • trees 2005-2006
    47. 47. Succession from mosses & lichens = pioneer speciesto shrubs & trees 2005-2006
    48. 48. Climax forest The species mix of climax forest is dependent on the abiotic factors of the region solar energy levels temperature rainfall fertility & depth of soil 2005-2006 birch, beech, maple, hemlock

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