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Chapter 26: Community Ecology - Coggle Diagram
Chapter 26: Community Ecology
Concepts
a
community
is a group of species that occur together at the same time and place.
Since the members of a community occur the same time and place, a community must have boundaries in both time and space.
Example of succession; each new group of organisms in a habitat alter it such that they themselves are excluded in new species come in. This occurs in many communities
Climax community-A stable self-aintaining community
Community restoration- Humans have started trying to recover nature lost due to human impact. Such as reintroducing wolves until Yellowstone national park and encouraging the migration of bears and mountain lions across the Rio Grande River from Mexico into big bend national park in Texas.
Population biology focuses on the members of a single species, their growth, interbreeding, survival, and so on.
Community ecology might examine that same species but would take into consideration its interactions with other species that occur with it
Community ecology is important to us because we are members of every community in which any human lives works plays or goes to reconnect with nature. As members of these communities, we affect the other organisms, and we would like to know what impact we are having.
Habitat loss/ habitat fragmentation- Caused by people building towns, mining for minerals, farming and so on.
By studying community colleges, we may be able to minimize the damage we do. We've already realized that wetlands are extremely valuable; not only do they have high species diversity, but They also filter harmful chemicals out of water, prevent erosion, and produce abundant animal life. Most cities and states not protect wetlands and dirt construction projects in the areas that are not as sensitive
Relocating a population of animals Scientist must set aside enough habitat in the correct habitat that will allow the animal to find food, mates for reproduction, and protection from predators.
Diversity
Community diversity varies. Some communities such as salt flats and have a few species, whereas others such as rain forests have thousands
What approach to quantifying community diversity as is done by measuring species richness, which is simply account of the species present. Discount is a species
checklist.
These lists are always incomplete because it is impossible to catalog every prokaryote and fungus species present.
There's other than species may be the objective of studies of diversity. Diversity of gratefulness may be the focus., Such as the presence, absence, and relative abundance of herbs, shrubs, and trees, or annuals, perennials, and ephemerals.
Diversity and scale
Scale
- can mean the overall extent of some region of space or time, and also the size of the smallest unit in a pattern or analysis
The relationship between area and species richness is called the
species-area relationship
and is expressed by the formula S=cA^Z
S=cA^Z. S is the number of species, a is the area, and c and z are constants that must be discovered by studying individual communities
Species abundance distribution
- describes the relationship between the number of species observed in a field study as a function of their observed abundance
Robert Whitaker proposed a means of measuring diversity at specific scales
Alpha diversity is the number of species or growth forms that occur at a local, small site.
Beta diversity compares differences between several small sites within a larger region. The region should be the larger community being studied; the comparison is between various parts within a forest, for example, between some in a forest and others in an unrelated desert.
Gamma diversity is the number of species within a region.
Diversity varies with latitude as well. Natural us noticed a far northern areas in Canada, Siberia, and Alaska have far fewer species (lower diversity) than similarly sized areas near the equator in the Amazon rainforest, central Africa, and southeast Asia. This is due greatly to the weather of the different areas.
We're just now obtaining new types of evidence that indicates that evolution or history is also fundamental contributor to the differences in diversity between tropical in highlighted to Darius. Until 50 million years ago, earths climate was much warmer than it is now, and tropical conditions covered almost all of earths land masses.
Predator-Prey Interactions
Population density possibility of a predator prey relationship
As the herbivore consumes more of the plant, the plant population decreases which in turn makes it more difficult for the predator to find food so it's population decreases also. The two populations may cycle up and down repeatedly.
The predator may consume so much of the pray that the prey population becomes low or even locally extinct which in turn because the predator to become locally extinct also. Such a predator prepare would not be part of a community for long
Other factors may limit the population of the predators such that it cannot be overconsumed the prey and both species remain at low, stable population sizes indefinitely
Feeding rate
- First how quickly a predator finds a new Prey individual, and
handling time
refers to the amount of time needed to actually consume the prey
These two together constitute the predators
functional response
Feeding rate will be faster if there are more prey individuals available, so a predators functional response is dependent on prey density it is
Prey dependent
The simplest model of single predator-single prey interaction is the Lotka-volterra model.
Which models the net rate of change in prey numbers as
dN/dt=rN-aNP In which dN/dt is the rate of change with time of the prey population. r is the intrinsic rate of increase for the prey species, N is the number of individuals of prey species in the community, a is the predators per capita attack rate, P is the number of predator individuals present. Do units of a or the number of pre-eaten per pray per predator per unit time; that is, a is also pray dependent
dP/dt=faNP-qP in which dP/dt Is the rate of change with time of the predator population. f is a constant Indicating the predators efficiency at converting the prey it is eating into new predators. q Is the predators per capita mortality rate (which is independent of population density.)
The population of prey will be stable, neither increasing or decreasing, when dN/dt=0 Can be expressed as
rN-aNP=0
rN=aNP
r=aP
r/a=P
The
prey
population is stable when the density of the predators equals r/a. The population of
predators
is stable when dP/dt=0 which can be expressed as
faNP-qP=0
faNP=qP
N=q/fa
Predator population will be stable when the density of prey equals q/fa.
The line indicating population stability is called a
zero growth isocline
paradox of enrichment
- Improving conditions for the Premier lead the predator to over exploit the prey in both species will be lost. This may be an important factor in the loss of species diversity want to habitat is "improved"
And example would be mineral rich pollution fertilizer streams and lakes, causing certain algae to proliferate but ultimately resulting in loss of many species.
If we would harvest just enough of a species to keep the population density at a certain point, the species would be stable and we would obtain what is called a
Maximum sustained yield
Fixed effort harvesting
- an alternative in which population health is determined by the amount of fish or deer etc. that can be harvested with a particular amount of effort. If populations were healthy, the harvest would be abundant; if populations are sparse, the harvest will be poor, but either way, harvesting must be stopped after a particular amount of time or effort.
Fixed quota harvesting
- Fisherman or hunters are allowed to harvest a particular amount, such as one day or per Hunter or a certain number of tons of fish per fleet, no matter how long it takes or how much effort is required. This quota varies based on the health and density of the population
Predator selection among multiple prey
There are many cases in which certain animals, especially insects, consume only a single plant species while ignoring all others. They will often only lay their eggs on one particular species, and then the larva eat only that species. Most animals especially vertebrate herbivores can and will eat a variety of plants and omnivores eat both plants and animals.
Optimal foraging theory
- behavioral ecology model that helps predict how an animal behaves when searching for food. Although obtaining food provides the animal with energy, searching for and capturing the food require both energy and time
This has produced an
Optimal diet model
That makes four predictions
Predator should evolve to prefer whichever prey yields the most energy per unit of handling time
If the high-yield prey becomes sufficiently scarce, then the predator would be more successful by broadening its diet to include prey that are lower in energy if they are abundant and easy to handle
Some prey items will always be eaten if they are encountered, others will never be eaten even if easy to obtain, for example if the edible parts are not worth the trouble of overcoming the plants defenses.
The probability that a particular plant will be eaten depends partly on the abundance of other plants that are easy to handle and have higher value. Less profitable prey will be ignored if more profitable prey is available
Competition between species
Several species often compete for the same resources; this is interspecies competition as compared to intraspecies competition.
Exploitation competition
- Resource competition occurs when the organisms actually consume a shared resource, that's making it less available for other organisms.
Interference competition
- One organism restricts another organisms access to resources even though the first might not be using it
Invasive species
- If a species can increase from very low population density even with its competitor present, then that species is invasive
Resource
- Any substance or a factor that can lead to increased growth rates as its availability is increased and that is consumed by an organism
Apparent competition
- When plants are not actually competing for and using a resource but there is an increase in one plant species associated with a decrease in others and they seem to be in competition
Beneficial interactions between species
Mutualism or mutualistic relationship
- When two organisms interact that has the outcome of both being benefited
Facilitation
- One organism helps another without receiving any benefit. The first organism
facilitates
the presence of the other
Plays a role in
primary succession
in which organisms become established on newly created substrates. For example, volcanoes produce new substrate in the form of lava flows are ash fields are completely sterilized a pool
nurse plants
- serve as protection to smaller plants
Metapopulation
Metapopulation
- If several local populations are interconnected by migration and gene flow between the patches, the local populations constitute this
A common model of meta-populations makes four assumptions
A region of the environment is composed of many discrete patches in which the species can live
Some patches are occupied by the species, where as other suitable patches or not.
Postulates that some patches are occupied by the species, others are not. Population size always vary with time due to the predators, competition, and disturbance
Empty patches will become colonized by migration from occupied patches.
Emphasizes the need for colonization of new patches by migration.
Populations within individual patches have a probability of going extinct within that patch.
Postulates that populations within a patch have a probability of going extinct locally. For some species is probability is low in a species persists for many generations and most patches, but for other species the probability is high in species occupies a patch only briefly
a
fugitive species
Is one that survives by colonizing new patches, flourishing temporally, and then colonizing more patches before it dies out an old ones. Many weeds of disturbed sites are fugitive species
Source habitat
- a high quality patch
in contrast, a
sink habitat
, is a low quality one
Assisted dispersal
- Animals are captured in one area and are released into a new area
Interconnectedness of species: food chains and food webs
The simplest communities typically have at least three tropic waffles: primary producers, primary consumers, and secondary consumers
food chain
- The direct line of consumption
food web
- If you trace all the prey of the top carnivores and then trace the food sources of each of those prey species in someone you obtain a network of numerous interrelationships called the food web
energy flow web
- A trace of how energy flows through the community via consumption of energy from food (plants and animals)
Keystone species
- a species on which other species in an ecosystem largely depend, such that if it were removed the ecosystem would change drastically.
