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Community Ecology (Beneficial interactions between Species (the concepts…

- - - - then predict that both species in a mutualistic relationship continue helping each other such that both population grow to infinity obviously that never happens
- - - - is attacked by only one species of predator, such as herbivore
    - - feeding rate refers to how quickly a predator find a new prey individual and handling time refers to the amount of time needed to actually consume the prey
      - the two together constitute the predators functional response
      - Feeding rate will be faster if there are more prey individuals available, so a predatory functional response is dependent on prey density, it is prey-dependent
      - the simplest model of single predator-single prey interactions is the Lotka-Volterra model .
        
        it models the net rate of change in prey number as dN/dt=rN-aNP
        
        in which dN-dt is the rate of change with time of they prey population
        
        r is the intrinsic rate of increase for the prey species
        
        a is the number predators individuals attack rate
        
        p is the number of predator individuals present
    - - that is , a is also prey-dependent; it is small if few prey are present, larger of prey are abundant.
      - the equation for the net rate of change of predator numbers is dp/dt =faNp - qP
      - f is a constant indicating the predators efficiency at converting the prey it has eaten into new predators
      - q is the predators per capita mortality rate
    - - may be an important factor in the loss of species diversity when a habitat is "improved
    - - theoretically, if we would harvest just enough of a species to keep the population density at that point the species would be stable and we would obtain
    - - in which population health is determined by the amount animals that can harvested with a particular amount of effort
    - - in which fisherman or hunters are allowed to harvest a particular amount of animals, no matter how long it takes or how much effort is required
  - - - there are many cases in which certain animals , comsume onle a single plant species while ignoring all others
      - but most animals, especially vertebrate herbivores, can and will eat a variety of plants and omnivores eat both plants an animals
    - - first is the probability that a particular prey individual will be encountered
      - second is the decision by the predator to attack an individual once it has been encountered
      - third is the probability that an attack prey item will be successfully eaten
    - - examine the interaction between these factors in an attempt to understands why herbivores eat the plants they do while ignoring others
      - plants are autotrophs, and although they also need both energy and mineral nutrients or water
        
        almost all plants have plenty of sunlight and thus plenty of energy so it often catches botanists by surprise that zoologists focus so heavily in energy
      - optimal diet model
        
        that makes four predictions
        
        second, if the high-yield become sufficiently scar, then the predator would be more successful by widening diet to include prey that are lower in energy if they are abundant and easy to handle
        
        third, some prey items will always be eaten if they are encountered, others will never be eaten even if easy to obtain
        
        first predators should prefer whichever prey yields the most energy per unit of handling time
        
        fourth, the probability that a particular plant will be eaten depends partially that a particular plant will be eaten depends partially on the abundance of together plants that are easy to handle
  - - - even though various species have different niches, most niches overlap at least somewhat with other niches
      - if two species are competing one or both grows or reproduces more poorly than it would if it had the entire habitat to itself
    - - resources competition occurs when the organisms actually consume a shared resource, thus making it less available for there organisms
      - Interference competition
        
        one organism restricts another organism access to resources even though the first might not be using it
    - - the results are that two competing species can coexist, if each species has a greater negative effect on its own per capita growth rate then it has on there capita growth rate of it competitors
      - two species can coexist in a community if each interferes with itself more than it interferes with the other
    - - is any substance or factor that can lead to increased growth rates as its availability is increased and that is consumed by an organism
  - - - in this case we say that the prey species share a predator
      - if all prey population are low, then the population of the predator is probably low also.
      - if something should cause the population of one of the prey species to increase
      - even if the predator prefers one species and consume other plants only incidentally, the larger predator population results in more herbivory on many plant species
        
        thus an increase in one plant species is associated with a decrease in others, and they appear to be in competition
        
        because the plants are not actually competing for and using a resource, this is called apparent competition
- - - - a larger area will have more variation in types of soil, topography, geology, and so on.
      - it has more diverse habitats so it can have more types of organisms, each adapted to particular aspects of the area
      - second, larger areas have larger populations than does any smaller sub regions of that area
    - - S=cA^z
      - in which the S is the number of species, A is the area, and c and z are constants that must be discovered by studying individuals communities
        
        once c and z are known for various communities, they can be used compare the diversity of those communities
  - - - perhaps one of the oldest and still most widely taught theories is that the tropical regions near the equator have relatively
        
        benign environments whereas those at higher latitudes have more severe conditions
      - near the equator, temperatures are always warm; freezing conditions are extremely rare exception the highest mountains.
        
        rainfall abundant with only occasional short period of dryness.
        
        plants do not have to adapt to survive freezing or water stress
    - - there is low diversity of plants in the high latitudes of of the southern hemisphere
      - the temperature latitudes of the northern hemisphere have more land but much of that too either is covered by ice or consist of mountain range whose peaks are frozen
      - tropical regions simply have more land available land for plants-primary producers - and thus more land for all sorts of organisms
  - - - which is simply a count of the species present .
    - - this count is a species
      - are always incomplete because it is impossible to catalog everything
- - - - because the members of a community occur at the same time and place
      - boundaries in both time in space
      - communities also have boundaries in time: they come into being and then cease to exist
    - - is important too us becauses we are members of every community in which any human lives
        
        works, plays or goes to reconnect with nature
    - - and in the process destroy some communities but permitting new ones to start
    - - some communities change as part of their very nature whereas other remain the same
    - - the more or less predictable sequence of change
      - pic
    - - the disturbed patch undergoes succession until it becomes spruce-fir forest again #
    - - restoring a community
      - pic