Please enable JavaScript.
Coggle requires JavaScript to display documents.
Chapter 26: Community Ecology - Coggle Diagram
Chapter 26: Community Ecology
Concepts
Community Ecology
A community is a group of species that occur together at the same time and place
Examines interactions between species
Disturbance
Competition
Predation
Mutualism
Commensalism
Communities must have boundaries in both time and space
Timewise, they come into being and cease to exist
Disturbances alter the territory and destroy communities but allow new ones to start
Communities change as part of their nature as others remain the same
Succession - The predictable sequence of changes over time of the species that occur in an area
Climax Communities remain stable and self-maintaining
Community Restoration
Work and projects carried out to alter a group of organisms back to a more natural state such as reintroducing species or removing dams
Population Biology
Members of a single species
growth
interbreeding
survival
Diversity
Diversity and Scale
Larger areas are more diverse than smaller ones
Large Environments
Can have more types of organism
Varies in soil, typography, geography, etc.
larger populations
More affected by disturbance
Species-Area Relationship
Relationship between Area and Species Richness
Calculated with S =
c
A^Z
S = number of species
c
and
Z
are constants that must be discovered by studying individual communities
Distinct Size Terms Used in Ecology
Local
A small area less than a few square kilometers
Region
Larger than a few square KM but much less than that of a continent
encompasses all members of many species and the process of speciation and extinction
Biome
A large region characterized by the dominant plants present that are influenced by their biome
Examples include temperate grasslands, temperate rainforests, tropical rainforests, deserts, and salt marshes
Biogeographical Region
An extremely large region that coincides with a continent or very large region bounded by a geological or climatic barrier to migration such as oceans, mountains, or deserts
Robert Whittaker's Diversity Scales
Alpha
The number of species or growth forms that occur on a local level
Beta
Compares differences between several small sites within a larger region
Gamma
Number of species within a region
Diversity and Latitude
Far northern latitudes have lower diversity than similarly sized areas near the equator
Equatorial Environments
Temperatures always warm
Rainfall is abundant
Plants do not have to adapt to survive freezing or water stress
"Northern" Regions
Receive little sunlight or warmth throughout winter
bitterly cold temperatures
Does not fully thaw even in summer, resulting in a permanently frozen layer of soil (permafrost)
Few organisms can adapt to these conditions
More land, but less accessibility
History
tropical conditions dominated Earth's land until 50MYA
Antarctica was farther north and not frozen over
Rockies, Andes, and Himalayas have not yet formed
Ferns and Conifers diverse at this time
40 MYA, global temperatures drop enough to form the Antarctic ice sheet
12 MYA, ice sheets began to cover the regions of Canada, Europe, and Russia
Oceans also became colder, causing dry temperate conditions
Adaption to Earth's changing environment occurred over millions of years
Richness
some communities have few species, while others may have thousands
Species Richness is a count of the species present
Quantified by a species checklist, which are impossible to fully complete
community ecology focuses only on several organism rather than all within a community
Factors of Species Diversity
Growth forms
Plant storage organs
primary producers, primary consumers, secondary consumers, and decomposer as well as their interactions
Genetic diversity measured through DNA technology
Predator-Prey Interactions
One Predator, One Prey
One species of prey is attacked by only one species of predator
The predator's population density will grow logistically with the growth of the population density of the prey
As a consequence of consuming too much prey, the predators also die off with the prey
Fundamental Aspects of this relationship
Feeding Rate
How quickly prey is found by the predator
Handling Time
Time needed to consume prey
Functional Response
If the functional response of the predator is dependent on prey density, it is prey dependent
Lotka-Volterra Model
Models the net change in prey numbers
dN/dt = rN - aNP
dN/dt = The rate of change with the time of the prey population
r = Intrinsic rate of increase for the prey species
N = Number of individuals of the prey species
a = The predator's attack rate per capita
Number of prey eaten per prey per predator per unit time
P = Number of predator individuals present
stable when the density of the predator = r/a
Equation for the net rate of change of predator numbers
dP/dt = faNP - qP
dP/dt - the rate of change with time of the predator population
f= A constant indicating the predator's efficiency at converting the prey it has eaten into new predators
q = the predator's per capita mortality rate
population of prey will be stable when dN/dt = 0
Predator population will be stable when density of prey = 1/fa
often criticized for being too simplistic
Predator Selection Among Multiple Prey
Choice of Prey
decision to attack
successful consumption of prey
Optimal Foraging Theory
Predators should evolve to prefer whichever prey yields the most energy per unit of handling time
If the high-yield prey become scarce, the predator would be more successful by broadening it's diet
Some prey items will always be eaten if encountered while others are not worth the energy
the probability that a particular plant will be eaten depends on the abundance of other plants available to the predator
Competition Between Species
Interspecies Competition
Plants compete for
light
Water
minerals
Exploitation competition
Resource competition occurs when organisms consume a shared resource
Interference Competition
One organism restricts another organism's access to resources even though the first might not be using it
Two competing species can coexist if each species has a greater negative effect on its own per capita growth rate than it has on the per capita of its competitor
Two species can also coexist if one or the other can increase from low density even in the presence of the other
Invasive Species
If a species can increase from very low population density in the presence of its competitor
Resources
Any substance or factor that can lead to increased growth rates as its availability is increased
abiotic
light
water
minerals
space
Biotic
attention of pollinators and other mutual helpers
Apparent Competition
One predator may prey on several species
If one of the prey species increases in abundance for any reason, that may lead to an increase in the predator population resulting in more predation
The increase of one prey species due to predation may cause the decrease in the other prey species, appearing to be competition
Metapopulations in Patchy Environments
If all species were to interact freely, we would speak of just one population rather than several
If several local populations are interconnected by migration and gene flow between the patches, the local populations make a metapopulation
Model of Metapopulations
A region of the environment is composed of many discrete patches in which the species can live
some patches are occupied by the species, whereas other suitable patches are not
Empty patches are not surplus, spare, or unneeded, just unoccupied
Empty patches will become colonized by migration from occupied patches
Populations within individual patches have a probability of going extinct within that patch
The various patches will be separated from each other by varying distances, and some patches will be larger than others
Some patches will be favorable and considered high quality patches
source habitat
Some patches will be unfavorable and considered low-quality patches
sink habitat
Migration Corridors
Interconnect patches
may be narrow, but requires resources
natural is better than artificial
Fugitive Species
One that survives by colonizing new patches, flourishing temporarily, then colonizing more patches before it dies out
Many weeds of disturbed sites
Migration between patches is becoming important due to global warming
due to industrialization, many natural corridors between the preferable patches are inaccessible
Assisted dispersal of organisms may help, but be risky in plants
Interconnectedness of Species: Food Chains and Food Webs
Communities typically have at least three trophic levels
Primary producers
primary consumers
secondary consumers
Studying Species interaction across trophic levels
Food chain
the direct line of consumption from producer to secondary consumer
food web
Tracing all prey of the top carnivores, to what producers the prey consumes, and so on, reflects a network of numerous interrelationships
majority of which are incomplete
most communities have a small number of strong food chains and a large number of lesser food chains
Energy FLow Web
mapping out which herbivores consume the most energy and trace the flow of energy throughout the system
difficult to construct for real communities
Keystone Species
A species that dramatically affects the structure of their community just by being present
difficult to identify without it being absent from the environment
even more difficult to discern through a food web or energy flow web
can be on any trophic level
Beneficial Interactions Between Species
Various organisms within a community often interact in ways that are beneficial
Mutualism
interactions in which both organisms benefit
Certain mutualistic interactions evolved from predation
pollination
Insects would devour the pollen of ancestral angiosperms, but eventually their regular visits aided the evolution of insect pollination
nitrogen-fixing bacteria may have been pathogenic
Mycorrhizal fungi may have also been pathogenic
Mutualism is not free
flowers have the cost of producing the pollen and nectar which the pollinator feeds on
plants must supply carbohydrates to the nitrogen fixing bacteria or mycorrhizal fungi
Pollinators must work to obtain nectar or pollen
bacteria and fungi must give their fixed nitrogen or phosphate
Cheating
Can become a facilitative interaction due to cheating, or obtaining benefits without giving something
Nectar robbing bees bite through petals in order to not waste energy struggling around the stamens, resulting in them not being dusted with pollen which would benefit the plant
Uncommon in nitrogen-fixing bacteria, although plants are known to quite literally break off the relationship if the soil is rich enough in needed compounds that giving something to get something is no longer needed
Mutualistic relationships will be selected for only as long as the benefits outweigh the cost
Nurse Plants
plants that alter a small area of habitat immediately below themselves that is more favorable to other nearby areas not below the nurse plant
Facilitation
Interactions in which one organism helps another without benefit
Both limited by predation
Competition and predation both necessary to prevent thousands of species from surviving within a community
Without this limit, all species would live everywhere
plays a role in primary succession, in which organisms become established on newly created substrates