Chapter 16: The Nature of Communities Flashcards
Communities
groups of interacting species that occur together at the same place and time
What are communities defined by (Physical Characteristics)?
Ex: all species in a sand dune, mountain stream, or desert
What are communities define by (Biological Characteristics)?
Ex: all the species associated with a kelp forest or a coral reef; implies importance of abundant species
What is an arbitrary way of defining a community?
Based on the questions they are posing
What can community subsets be defined by?
-Taxonomic affinity
-Guild
-Functional Group
Guild
a group of species that use the same resources
Functional Group
species that function in similar ways
What do food webs organize?
Organize species based on trophic or energetic interactions
Trophic Levels
-Primary producers: autotrophs
-Primary Consumers: herbivores
-Secondary Consumers: carnivores
-Tertiary Consumers: carnivores
Interaction Webs
more accurately describe both trophic (vertical) and non-trophic (horizontal) interactions
Negatives of Food Webs
-tell little about strength of interactions or their importance in the community
-species can span multiple trophic levels
-rarely include important elements such as symbionts and detritivores
-Dont include nontrophic interactions
Horizontal Interactions of a food web
competition and positive interactions
Community Structure
-set of characteristics that shape communities
-provides basis for generating hypotheses and experiments to understand how communities work
What is the most common measure of community structure?
species diversity
What does species diversity combine?
-species richness (number of species)
-species evenness (relative abundance)
Slide 22
Biodiversity
describes diversity at multiple spatial scales, from genes to species to communities
Implicit
interconnectedness of all the components
Rank Abundance Curves
plot the proportional abundance of each species relative to others in rank order
Species accumulation curves
-species richness plotted as a function of total number of individuals counted
-help determine when most or all of the species in a community have been observed
Hughes et. al (2001)
-compared species accumulation curves for five different communities
-the communities varied greatly in amount of sampling effort needed to determine species richness
-temperate forest and tropical bird species were adequately represented before half the individuals were counted
-for tropical soil bacteria, more effort was needed to sample this extremely diverse community
Importance of Spatial Scale in Hughes et al (2001)
-If tropical soil bacteria were sampled at the same scale as Costa Rica moths, the bacterial diversity would be immense in comparison
-the study highlights how little we know about community structure of rarely studied assemblages, such as microbial communities
Species Composition
-identity of a species in a community
-two communities could have identical species diversity values but completely different species
-the density of species is critical to understanding community structure
Direct interactions
occur between two species (competition, predation, facilitation)
Indirect Interactions
relationship between two species is mediated by a third (or more) species; often discovered when species are removed to study direct interactions
Trophic Cascade
rate of consumption at one trophic level results in change in species abundance or composition at lower trophic levels
Trophic Facilitation
a consumer is indirectly facilitated by a positive interaction between its prey and another species
Competitive Networks
interactions among multiple species in which every species has a negative effect on every other species. No one species dominates the interaction, allowing for coexistence
Buss and Jackson (1979)
hypothesized that competitive networks allow coexistence of competitors and thus maintain species richness
Interaction Strength
magnitude of the effect of one species on the abundance of another
How is interaction strength measured?
measured by removing one species (interaction species) from the community and observing the effect on the other species (target species)
Slide 49
Interaction strength may depend on ____
environmental factors
Menge et al. (1996)
-measured interaction strength of sea star predation on mussels in wave-exposed versus wave-protected areas
-Interaction strength was greater in protected areas. Pisaster was a less efficient predator in crashing waves
Foundation Species
large or abundant species, such as trees, that provide food or habitat for other species
Effects of foundation species
have large community wide effects, and thus species diversity, by virtue of their considerable abundance or biomass
-they may also be good competitors for space, nutrients, or light
Ecosystem Engineers
create, modify, or maintain physical habitat for themselves and other species
Keystone species
have strong effects because of their role in a community
Effect of Keystone Species
their effect is large in proportion to their biomass or abundance
Can keystone species also be ecosystem engineers?
Yes
Ocean acidification
the oceans absorb atmospheric CO2, which reacts with seawater to lower pH
Alsterberg et al. (2013)
studied algae and consumers in an estuarine community
