Intro to Community Ecology Flashcards
What is a community in ecology?
- an association of interacting species inhabiting a defined area at a particular scale over a particular span of time
- communities are often considerations of a particular group (taxonomic, guilds, life form, funcitonal)
Guild
species living in the same way
- e.g., use same resources
life form
species that have a similar growth form
functional group
species with a similar ecological function or attribute
What Types of Species are in Community Ecology? (three types)
- foundational species
- keystone species
- invasive species
Foundational species
- species which provide a key role in shaping structure within a community
- e.g., coral reefs (provide food, shelter, breeding areas, and refuge for marine life)
Keystone species
- species that have a disproportionate impact the community structure relative to the abundance of other species
- if removed the loss of keystone species leads to a dramatic change in structure
Invasive species
- species that are not native to the habitat and disrupt the community
- characterized by an inability to grow quickly and reduce local biodiversity
How is Community Structure Described?
- the relative abundance of species within the community
- the number of species and diversity
- species composition
What is community diversity a combination of?
the total number of species there are as well as their relative abundance
Species richness
the number of species in a community
Species Evenness
the relative abundance of the various species within a community
Species Diversity
a measure of diversity that increases with species evenness and species richness
What is Species Abundance and how is it measured?
- measure of how common or rare a species is
- measured depending on the life history of the species in particular
- number of individuals, species cover, species biomass
Number of Individuals
- a measure of species abundance
- used when organisms form distinct entities, like birds
- not useful for clonal organisms
Species Cover
- a measure of species abundance
- visual estimation
- used when identifying individuals is not trivial, like in algae, plants
- quick and non-destructive but less precise
Species Biomass
- a measure of species abundance
- quantifiable as fresh or dry weight
- used when identifying individuals is not trivial like in plants
- slow and destructive, but more precise methods
Species Dominance and Why is it Important?
- species that is more common than all others
- may be measured as biomass, area occupies, # of individuals, etc.
- most species in the community will occur in moderate abundances
- is important because if only one or two species dominate a community, a majority of the interaction within that community will involve those species
Species Abundance Distributions
- abundance is usually quantified in relative terms - and graphed using a lognormal distribution
- aka population size with respect to the total number of individuals in a community, regardless of species or percent cover with respect to the total area of a patch
Why are Abundance Curves not always ideal
- how well we can fit a lognormal distribution curve depends on sampling effort
- overlooking rare species happens often
- the more you sample, the more species you will find and the closer your abundance distribution will resemble a lognormal distribution curve
What are the three types of species diversity? What is their significance?
- Gamma: diversity within a region/landscape
- Alpha: diversity within a particular area within a region/landscape (a subset of gamma)
- Beta: a measure of the diversity among locations within a region, usually measured as the amount of species change between ecosystems calculated as gamma/alpha
What is Species Evenness?
- the relative population size of each species
- an ecosystem dominated by one species will have low evenness
What is Biodiversity and how is it calculated?
- biodiversity is species richness AND evenness
- calculated by the Shannon-Wiener Diversity Index (H’)
How do we calculate Species Evenness?
- using Pielou’s J
- J= H’ / ln(s)
How do we determine how even a community is using Pielou’s J
- closer to 1 = more even
- closer to 0 = less even
Rank Abundance Curves, and What is their Significance ?
- they are a plot of relative abundance of species
- these are useful because they allow ecologists to visually portray species dominance/diversity patterns within a singly community or among communities
Explain how to read a rank abundance curve
- each dot represents the relative abundance of a species
- dots ranked according to their abundances, with high-abundance species plotted on the left side of the curve
- the flatter the curve (aka decreased), the more even the community
What are the factors that increase/decrease biodiversity?
- time: the more uninterrupted time to evolve/colonize, the higher biodiversity
- global change: pollution, habitat destruction, landscape homeogenization, invasive species decrease biodiversity
- complexity: the more complex, the higher biodiversity
- exploitation and limitation: some predators or herbivores, or nutrient limitation decrease competition and increase biodiversity
What is included in a more complex environment?
vertical structure, water movement, nutrient availability, light availability,etc
What is species composition?
the species that occur in a given community at a given time
Why is considering species composition important?
ecological functions performed by communities are dependent upon community structure
- compositional changes can indicate shifts due to environmental or anthropogenic effects
- concern rises when compositional shifts impact the delivery of ecological services - processes that are of value to humans
What are some examples of ecological services?
- biomass production
- carbon sequestration
- nutrient cycling
- crop pollination
- water filtration
- etc.
How does species diversity influence ecological function? (three main mechanisms)
- complementarity
- facilitation
- species selection/sampling effect
Define Complementarity
- comes from niche theory
- a given ecological service will be at its greatest for communities in which all resources and/or microenvironments are being exploited/occupied
Define Facilitation
- some species may enhance the growth of others
- ex. reducing soil salinity and/or altering the thermal environment
- may be particularly important in stressful situations
What is species selection/sampling effect?
- basic idea is that species differ in the inherent rates of delivery of ecological services
- as the number of different species increase in a community over time, the odds of said community containing at least one species with enhanced function increases
genetic diversity and ecological function relationship
- increases in genetic diversity can lead to an increase in species diversity within a community
- how? genotypes likely differ in : how species forage to resource, where plants put roots and leaves, susceptibility to disease, ability to outcompete rivals,etc.
Are lakes simple or complex?
complex, have horizontal and vertical spatial complexity and can turn over
