Community (Diversity, Structure, Disturbance) Flashcards
Disturbance
an event of intense environmental stress occurring over a relatively short period of time and causing large changes in the affected ecosystem
Intermediate disturbance hypothesis
Species diversity will be highest in communities that experience intermediate levels of disturbance
Community
an association of interacting species inhabiting some defined area
Community structure
Based on the INTERACTIONS of all species in a community.
How abiotic & biotic factors influence the number of species, relative abundance of species, and the types of species in an area
Guild
One type of organism that make their living the same way
How abundant are most species?
Moderately abundant.
Species richness
Number of species in a community
Species evenness
Relative abundance of species
What are metrics we can use to describe community diversity?
(1) Species richness
(2) Species evenness
(3) Shannon-Wiener index (H’)
(4) Simpson Index (y)
(5) Rank-Abundance Curve
Shannon-Wiener Index
H’ increases with increasing richness and evenness
H’ = - Σplnp
Simpson Index
y is the probability that any two individuals drawn from a community will be of the same species. (0 = high diversity)
y = Σp^2
D = 1 –Σn(n-1)/N/(N-1)
Rank-abundance curve
Plots proportional abundance (y) relative to abundance rank (x). Lower slope = greater evennes.
What are factors that influence community diversity?
(1) Environmental complexity
(2) Species interactions
(3) Disturbances
What can increase community diversity?
(1) Increasing environmental complexity (heterogeneity=more niches)
(2) Predation and competition (greater partitioning of resources/space)
(3) Intermediate disturbance
Compare community diversity with community structure
Community diversity = # different species in a community.
Community structure = interactions of all species in a community
Primary producers
Chemo/photoautotrophs
Primary consumers
Herbivores that eat primary producers
Secondary consumers
Carnivores that eat primary producers
Tertiary consumers
Carnivores that eat other carnivores
Food web
Diagram showing feeding relationships among organisms within an ecosystem
What is the relationship between the number of feeding interaction between species with the overall diversity of the community?
feeding interactions is INDEPENDENT of the overall diversity of the community.
What is the relationship between the number of trophic levels between species with the overall diversity of the community?
trophic levels increases with species richness. So higher community diversity is associated with increased food web complexity.
How are food webs and community diversity related?
Diversity is independent from the # of feeding interactions, but the #trophic levels (food web complexity) tends to increase with community diversity.
Connectedness web
Shows feeding relationships among organisms
Energy flow web
Shows connections quantified as energy flux
Functional web
Emphasize the influence of populations on growth rates of other populations
Food webs are defined in terms of…?
(1) Feeding interactions
(2) #trophic levels
What are indirect interactions of food webs?
(1) Indirect commensalism
(2) Apparent competition
(3) Trophic cascades
Indirect commensalism
Activities of one species indirectly benefit another species without itself being harmed or helped
Apparent competition
when negative impacts on species increase due to two species sharing a predator, or by one species facilitating the population growth of a predator for the other species.
What are the types of trophic cascades?
(1) Bottom-up
(2) Top-down
Keystone species
species whose interactions (usually feeding) have a disproportionately large influence on the structure of their community.
Altered stable state
Results from the loss of a habitat’s keystone species. Altered stable state is a habitat’s shift from an established community structure to a new one.
What is the impact of introduced/invasive species on community structure?
Simplifies community structure complexity by eliminating trophic levels. Diversity (α) isn’t decreased at the site, but diversity between sites (β) is decreased.
What are the energy flow constraints of energy transfer through the food web?
(1) Limited assimilation
(2) Respiration
(3) Heat loss
Assimilation (growth) efficiency
Percentage of what is initially consumed that becomes incorporated into the consumer
About ___% of biomass is lost when transferred from between trophic levels. The ecological efficiency is ___%.
90%; 10%
As trophic levels increase, biomass ___.
Decreases.
The most productive ecosystems have a maximum of ___ levels.
6.
What are the types of disturbances?
Source: Natural vs Anthropogenic
Space: Small vs Large
What kind of species will thrive under conditions of HIGH disturbance?
Weedy, fast growing
What kind of species will thrive under conditions of LOW disturbance?
Competitively superior/dominant
What kind of species will thrive under conditions of MEDIUM disturbance?
Balance–diversity of species
What are the types of succession?
(1) Primary - new substrate
(2) Secondary - old substrate available
Primary succession
Community development on new or newly exposed geological substrate.
Secondary succession
Community development after a disturbance removes the community of organisms but not the soil and organics.
Pioneer species
Early successional species. The first species to colonize an open area after a disturbance. These species tend to be hearty plants with N2-fixing bacteria and deep roots.
Climax species
Late successional species. the last assemblage of species to establish themselves in a habitat. The community remains in a stable state until a disturbanceresets the system. These species tend to be slow-growing, long-lived, and highly efficient competitors.
How long does succession take?
Depends on (1) type and (2) composition of community
What are some mechanisms of succession?
(1) Facilitation
(2) Inhibition
(3) Tolerance
Facilitative succession
Pioneer species are the only ones capable of colonizing during early stages of succession. They modify their environment so that it becomes less suitable for them, but more suitable for later successional species.
Inhibitive succession
Earlier occupants of an area modify the environment in a way that makes it less suitable for both early and late successional species. Late successional species can only get a foothold in an area if space is opened up by the death of earlier successional species. Late successional species eventually dominant because they are long-lived and are able to resist biotic and physical stress that wipes-out earlier successional species.
Tolerance
all species tolerant of the conditions in a particular environment (even climax species) can be present in pioneer community. Final composition reflects the environment’s selection.
What are the systems/patterns of disturbance?
Autogenic (stable, biotic) vs allogenic (unstable, abiotic) succession
Autogenic succession
Biotic elements of a community are driving succession to a stable, unchanged equilibrium
Allogenic succession
Abiotic elements (disturbances, weather) prevent a community from reaching equilibrium
Resistance
the ability of a community to maintain
structure/function in the face of disturbances,
Resilience
the ability of a community to bounce back
after a disturbance.
What happens if the underlying environment changes?
(1) Environment composition change –> phase shift, change in community composition
(2) Pulse event (predator removal) –> Altered stable state
