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ecology part 2, delta N- change in population size, delta t- time interval…

- - - - 4 factors that affect population- immigration,emmigration, birth rates, death rates
    - - common dispersion patterns
        
        clumped- individuals are aggregated in patches
        
        ex-Mushrooms, for instance, may be clumped within and on top of a rotting log.
        
        uniform- evenly spaced
        
        ex- Some plants secrete chemicals that inhibit the germination and growth of nearby individuals that could compete for resources.; territory
        
        random- position of each individual in a population is independent of other individuals
        
        ex- Plants established by windblown seeds, such as dandelions, may be randomly distributed in a fairly uniform habitat
    - - life tables- survival and reproductive rates of individuals in specific age-groups within a population
        
        To construct a life table, researchers often follow the fate of a cohort, a group of individuals of the same age, from birth until all of the individuals are dead. Building the life table requires determining the proportion of the cohort that survives from one age-group to the next
      - survivorship curves
        
        1-flat at the start, reflecting low death rates during early and middle life, and then drops steeply as death rates increase among older age-groups
        
        2- Type II curves are intermediate, with a constant death rate over the organism’s life span
        
        3- drops sharply at the start, reflecting very high death rates for the young, but flattens out as death rates decline for those few individuals that survive the early period of die-off
      - reproductive rates
        
        demographers view populations in terms of females giving rise to new females
  - - - delta N / delta t = B - D
    - - carrying capacity- The maximum population size that can be supported by the available resources, symbolized as K
  - - - three key components of an organism’s life history
        
        when reproduction begins (the age at first reproduction or age at maturity)
        
        depends on the species; A typical loggerhead turtle is about old when it first crawls onto a beach to lay eggs. In contrast, the coho salmon (Oncorhynchus kisutch) is often only three or four years old when it spawns
        
        how often the organism reproduces
        
        The coho salmon is an example of organisms that undergo a “one-shot” pattern of big-bang reproduction, or semelparity
        
        semelparity- one time reproduction
        
        iteroparity- repeat reproduction
        
        As an example, a female loggerhead turtle produces four clutches totaling approximately eggs in a year
        
        how many offspring are produced per reproductive episode
        
        Some species, such as the white rhinoceros (see Figure 53.11), produce a single calf when they reproduce, while most insects and many plants produce large numbers of offspring
      - trade offs
        
        No organism could produce thousands of offspring yet provision each of them as well as does a white rhinoceros caring for its single calf. There is a trade-off between the number of offspring and the amount of resources a parent can devote to each offspring
        
        In Eurasian kestrels, for example, caring for a larger number of young lowered the survival rates of the parents (Figure 53.13). In another study, in Scotland, researchers found that female red deer that reproduced in a given summer were more likely to die the next winter than were females that did not reproduce
        
        selective pressures- Plants and animals whose young have a low change of survival often produce many small offspring
        
        extra investment on the part of the parent greatly increases the offspring’s chances of survival
      - k-selection- selection for traits that are advantageous at high densities; operate in populations living at a density near the limit imposed by their resources (the carrying capacity, ), where competition among individuals is stronger
        
        Mature trees growing in an old-growth forest
      - r-selection- selection for traits that maximize reproductive success in uncrowded environments (low densities); maximize , the intrinsic rate of increase, and occurs in environments in which population densities are well below carrying capacity or individuals face little competition
        
        Such conditions are often found in disturbed habitats that are being recolonized. Weeds growing in an abandoned agricultural field
  - - - For example, researchers found that the mortality of dune fescue grass (Vulpia fasciculata) is mainly due to physical factors that kill similar proportions of a local population, regardless of its density
      - Variation in density-independent factors such as temperature and precipitation can cause dramatic changes in population size
    - - Researchers found that reproduction by dune fescue declines as population density increases, in part because water or nutrients become more scarce. Thus, the key factors affecting birth rate in this population are density dependent, while death rate is largely determined by density-independent factors
      - competition for resources
      - disease
        
        disease affects more people in the city than a rural area
      - territoriality
      - toxic wastes- ethanol that accumulates in wine is toxic to yeasts and contributes to density- dependent regulation of yeast population size
      - intrinsic factors
- - - - predation- +/- interaction, with a positive effect on the survival and reproduction of members of the predator population and a negative effect on members of the prey population
        
        defensive adaptations in animals
        
        aposematic coloration- he bright warning coloration of many animals with effective physical or chemical defenses
        
        cryptic coloration- camouflage
        
        mechanical defense
        
        chemical defense
        
        Batesian mimicry- harmless species mimics a harmful one
        
        mullerian mimicry- two unplayable species mimic each other
      - herbivory- +/- an organism—an herbivore—eats parts of a plant or alga, thereby harming it but usually not killing it
      - parasitism- +/- exploitative interaction in which one organism, the parasite, derives its nourishment from another organism, its host, which is harmed in the process
        
        endoparasites- Parasites that live within the body of their host, such as tapeworms
        
        ectoparasites- parasites that feed on the external surface of a host, such as ticks and lice
      - competition- -/- individuals of different species each use a resource that limits the survival and reproduction of both individuals
        
        Lynx and foxes in the northern forests of Alaska and Canada compete for prey such as snowshoe hares
        
        ecological niche- the sum of a species’ use of the biotic and abiotic resources in its environment
      - mutualism- +/+ interaction in which the survival and reproduction of individuals of each species is increased in the presence of the other
      - commensalism- An interaction that benefits the individuals of one of the interacting species but neither harms nor helps the individuals of the other species
  - - - latitudinal gradients
        
        Two key factors that can affect latitudinal gradients of species richness are evolutionary history and climate
        
        The species richness of plants and animals correlates with measures of evapotranspiration
        
        evapotranspiration- The total evaporation of water from an ecosystem, including water transpired by plants and evaporated from a landscape, usually measured in millimeters and estimated for a year
      - area effects
        
        species area curve- The biodiversity pattern that shows that the larger the geographic area of a community is, the more species it has
      - island equilibrium
        
        As the number of species already on the island increases, the immigration rate of new species decreases, because any individual reaching the island is less likely to represent a species that is not already present. Moreover, as more species inhabit an island, extinction rates on the island increase because of the greater likelihood of competitive exclusion
    - - effects on community structures-
        
        coral reefs- When the corals die, they become overgrown by algae. Surgeonfish and other herbivores that feed on algae come to dominate the fish community. Eventually, the corals topple because of damage from storms and other disturbances. The complex, three-dimensional structure of the reef disappears, and diversity plummets
        
        terrestrial
      - community ecology and zoonotic diseases
        
        zoonotic pathogens- hose that are transferred to humans from other animals, either through direct contact with an infected animal or via an intermediate species, called a vector
        
        Human activities, such as climate change and the destruction of natural habitat for urban or agricultural development, increase the risk of zoonotic disease by allowing animal carriers of disease to move into new geographic regions and by increasing the contact people have with wild animals
    - - intermediate disturbance hypothesis- The concept that moderate levels of disturbance can foster greater species diversity than low or high levels of disturbance
      - ecological succession- transition in the species composition of a community following a disturbance; establishment of a community in an area virtually barren of life
        
        primary
        
        secondary
      - human disturbance
  - - - only about 10% of the energy stored in the organic matter of each trophic level is converted to organic matter at the next trophic level
    - - beaver