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ap bio unit 8 review

Basics of Ecology

How Organisms Respond to Environmental Changes

  • survival of organism: depends on their ability to respond to changes in the environment
    • responses to changes can be behavioral or physiological
  • stimulus: change in the environment that triggers a response
  • behavioral response: refers to how animals cope or deal with changes in their environment by changing their behavior
  • physiological response: refers to how animals cope or deal with changes in their environment by changing their physiological processes/habits
  • example:
    • stimulus: extension of day length
    • behavioral response: many bird populations tend to migrate elsewhere
    • physiological response: some animals slow their metabolism to conserve energy
  • stimulus can be communicated between organisms to trigger changes in behavior with other organisms; they can communicate with:
    • audible signals: birds use audible signals to send warnings to other birds or to attract mates; some primates use vocalization to assert dominance or warn of the presence of predators
    • chemical signals (pheromones): can be released by some organisms to illicit a response in other organisms; responses can be mating, warning others, to scare off predators, etc.
    • electrical signals: sharks and rays can send electrical signals throughout the water to locate prey species
    • tactile signals: touching between primates can be used to express affection or to indicate dominance; some plants curl up to protect sensitive parts of their bodies from damage
    • visual signals: some species use warning coloration to scare off predators
    • aposematism: the use of warning coloration to inform potential predators that an animal is poisonous, venomous, or otherwise dangerous
  • signals can be used to establish hierarchy, find mates, and find resources
    • natural selection will favor signals and responses that increase survival and the chance of successful reproduction; over time this can lead to evolution of the population
  • cooperative behaviors: can lead to increased fitness of individuals and populations; it is cooperative if it is beneficial to another organism, the recipient, and is selected, at least partially, due to the benefits to the recipient
    • example: meerkats take care of each other; they huddle together for warmth, groom each other, forage together, fend off predators together in groups, etc.

Energy Flow Through Ecosystems

  • organisms use energy to reproduce, grow, and maintain organization; different species have different adaptations for maintaining energy levels (and body temps.)

  • endotherms: use thermal energy generated from their metabolism to maintain body temp. (ex. mammals, birds)

  • ectotherms: do not have internal mechanisms for maintaining body temp.; absorb heat from the environment; their behaviors will change depending on their body temp. (ex. fish, reptiles, amphibians)

  • metabolic rate: the total amount of energy an organism uses per unit of time

    • smaller organisms: higher metabolic rate because they have greater SA:V ratios and lose heat more quickly; higher metabolic rates compensate for the quicker loss of heat
    • larger organisms: lower metabolic rate because they lose heat less quickly

  • net energy gain: can result in energy storage (ex. fat tissues of animals)

  • net energy loss: can result in loss of mass or death of organism

  • changes in energy availability can affect population sizes (less energy = smaller population supported)

  • trophic levels: represent steps in the food and energy transfers between organisms in an ecosystem

    • organisms are classified into trophic levels based on their food and energy sources

    trophic level diagram

  • food chains: show the transfer of energy between trophic levels; direction of arrows in food chain show direction of energy flow between organisms

  • food webs: show the interconnections between organisms in different food chains; provide a more complete representation of energy transfers in ecosystems

    • autotroph (producers): get energy from physical or chemical sources in the environment
    • photoautotrophs: get energy from sunlight (ex. plants)
    • chemoautotrophs: obtain energy from small inorganic molecules (ex. bacteria)
    • heterotroph: get energy from carbon compounds made by other organisms; obtain energy from carbs, lipids, or proteins by breaking down the macromolecules using hydrolysis (ex. animals)
    • decomposers: break down dead organic material to allow for the recycling of nutrients in the ecosystem (ex. fungi)
    • detritivores: organisms that obtain energy by consuming organic waste of dead plants/animals (ex. earthworm)

    food chain vs food web

  • kleptoplasty: an unusual strategy for obtaining energy; when a heterotroph consumes an autotroph that it uses as a food source but then removes the chloroplasts from the autotroph’s cells to incorporate them into their own cells

  • energy is lost as it moves through trophic levels; it can be lost as heat or being consumed for necessary metabolic processes in organisms

    • more energy is required but harder to obtain in higher trophic levels, resulting in a smaller population (ex. there are less bears (top level) than there are bacteria (bottom level))
    • biomass: the total quantity or weight of organisms in a given area or volume.; increases as you go down trophic levels (producers have greatest biomass)

Regulation in Ecosystems

  • bottom-up regulation: in which the population size of producers decreases, so the population of subsequent (higher) trophic levels also decreases

  • top-down regulation: when animals at higher trophic levels limit population sizes at lower levels

    • if the predators (top level) are removed, the trophic levels in between predators and producers could increase due the lack of population control of them

  • availability of food and energy resources affects organisms’ reproductive strategies

    • organisms in unstable environments: produce a larger number of offspring to increase chance of survival
    • organisms in stable environments: produce fewer offspring because likelihood of survival is increased

    top-down vs bottom-up regulation

Population Ecology, Community Ecology, and Biodiversity

Population Ecology

  • population: made up of individual organisms that interact with one another and with their environment in complex ways

    • population sizes and population growth are affected by how organisms obtain the energy and matter they need to survive
    • population growth depends on:
    • population size (N)
    • birth rate (B)
    • death rate (D)

  • population growth rates are calculated as the change in population size over the change in population time: dN / dt

    • calculating population growth can be with: dN / dt = B - D
    • if birth rate exceeds death rate, population size will increase
    • if birth rate is less than death rate, population size will decrease
    • exponential growth: if there are no limiting factors (ex. abundance of food) on a population, it will experience exponential growth and can be described with the following equation:
    • N: population size
    • rmax: maximum per capita growth rate of the population
    • the larger the population size, the higher the growth rate and the faster it will grow

  • some populations eventually exceed the resources of their environment, meaning the growth is limited by resource availability

    • density-dependent factors: disease, predation, competition (for food, habitat, mates, etc.)
    • density-independent factors: temp., precipitation, natural disasters
    • both result in logistic growth of population, with the following equation
      • N: population size
      • rmax: maximum per capita growth rate of population
      • K: carrying capacity of environment
      • carrying capacity: the maximum population that can be supported by the available resources
      • as population size increases (N gets closer to K), the rate of population growth decreases

    exponential growth vs logistic growth

K-Selected vs. r-Selected Populations

  • K-selected: possess relatively stable population sizes at or near the carrying capacity of the environment
    • k-selected populations usually reproduce more than once per lifetime, with few offspring per reproductive cycle
    • invest greater levels of parental care in their offspring, resulting in higher survival rates of offspring
    • usually experience logistic growth and are sensitive to density-dependent factors
    • examples: most mammals, birds
  • r-selected: live in unstable environments
    • usually reproduce at a younger age and only once per lifetime with large numbers of offspring
    • invest less time in offspring, resulting in lower rate of survival for offspring
    • experience “boom or bust” periods, in which periods of exponential growth lead to populations that far exceed the carrying capacity (“boom”), resulting in rapid decreases of population ('“bust”)
    • usually not sensitive to density-dependent factors
    • examples: many fish, amphibians

Community Ecology and Simpson’s Diversity Index

  • community: a group of interacting populations living in the same habitat; described by their species composition and species diversity

    • species composition: number of species in a given area
    • species diversity: reflects the number of species in an area and the number of members in each of those species
    • species diversity gives a more accurate assessment of the variety of organisms found in an area

  • simpson’s diversity index: way of representing species diversity with the following equation:

    • n: total number of organisms of a particular species
    • N: total number of organisms of all the species
    • the higher the SDI, the more diverse the community

Relationships Within Communities

  • interactions can change over time

    • changing interactions can influence how many members of the community access the matter and energy they need to survive

  • competition: organisms compete for resources (ex. food, habitats, mates)

    • interspecies competition: between members of two different species
    • intraspecies competition: between members of the same species
    • any competition can lead to the demise of an organism in an ecosystem

  • predator/prey: predator species eat prey species and depend upon prey populations for food

    • insufficient numbers of prey species will lead to a decline in the predator species
    • increasing number of prey species will lead to an increase in predator species
    • fluctuation in the number of predators will generally follow fluctuations in the number of species
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  • niche partitioning: competing species may coexist if they use the resources available in their habitats differently

    • dietary partitioning: where organisms eat different prey/sources of food, so they can co-exist peacefully

  • trophic cascades: refers to the far-reaching effects of the reduction of one trophic level in a food web

    • example: decrease in sea otters lead to an increase in sea urchins because sea otters eat sea urchins

  • parasitism: a symbiotic relationship where one species benefits from the relationship but the other is harmed; negative relationship

  • commensalism: one species benefits and the other species neither benefits nor is harmed by the relationship; neutral relationship

  • mutualism: both species benefit from the given relationship between them; positive relationship

Biodiversity

  • biodiversity: refers to the variety of living organisms in an ecosystem
    • high biodiversity: increased resilience and more adaptable to changes in the environment
    • low biodiversity: less resilience and cannot adapt as well to changing environments
  • biodiversity depends on abiotic and biotic factors:
    • abiotic: non-living factors; influence the types and the number of species that can survive in the environment
    • ex. climate, water availability, etc.
    • biotic factors: living factors; limit how many consumers can survive in the environment
    • ex. number of producers
  • biodiversity of an ecosystem will influence the structure of food chains and food webs found in that ecosystem
  • keystone species: have a disproportionately large effect on an ecosystem compared to their population size
    • when a keystone species is removed from the environment, the ecosystem may collapse

Disruptions to Biodiversity

  • invasive species: a type of disruption to the ecosystem; a non-native species that causes struggle within the populations of the native species (ex. increases competition, introduces disease, etc.)
  • human impacts:
    • habitat destruction (as urbanization increases)
    • diseases (humans can come in contact with new species and pass off pathogens to them)
    • pollution
  • geological events: natural disasters (ex. volcanic eruption, flood) can decrease plant and animal diversity; prolong droughts can change biodiversity
  • disruptions in ecosystems can lead to evolution in populations
    • changed environments will select for adaptations that provide advantages in the environment
    • adaptations are generate by mutations, which are random, but selection for them is not random
  • rapid changes in environments can accelerate the pace of evolution