Lecture 27 - Assemblages Flashcards
communities
organisms interacting with other species (interspecific)
primary characteristics of communities
- diversity
- trophic structure
Explain how the presence of a particular species can influence how a community is structured
- > bottoms-up vs top-down control
- > dominant species are the most abundant in the community/consist of highest biomass
- > keystone species are not abundant but play pivotal ecological roles
- > ecosystem engineers (foundation species) change the physical environment
keystone species
a species which has a disproportionately large effect on its natural environment relative to its abundance
species composition
number and variety of organisms
species richness
absolute number of species
relative abundance
proportional representation of each species
advantages of higher-density communities
- > more productive
- > able to withstand and recover from stress
does productivity increase with diversity?
- > it was heavily belived that productivity would increase with diversity amongst all species but this is false
- > however, productivity DOES increase with diversity IN SOME CASES but is NOT UNIVERSAL
How is water a good predictor of diversity
- > evapotranspiration is a good indicator of the area’s water availability, solar radiation and temperature
- > higher levels evapotranspiration indicates higher tree species richness and higher levels of vertebrate species richness
evapotranspiration
disturbance
event that removes organisms or alters resource availibility
- > moderate levels of disturbance promote diversity
- > frequency and intensity of disturbance influence species diversity
ecological succession
gradual colonization and continual replacement by a variety of species
primary vs secondary succession
primary
- > the area is previously uninhabited when the gradual colonization occurs
secondary
- > area with previously established community and/or soil
humans __________ and __________ disturbance
humans alter and cause disturbance
trophic structure
feeding relationship
- > food chain
food chain vs food web
- > food chain is linear hierarchy of organisms
- > food web is the more realistic representation of the relationships between organisms of a community
- > food chain is also embedded in the food web

why are trophic structures/food chains usually fewer than 5 levels
- Energetic restrictions
- > only around 10% of energy stored as organic matter at one level is converted to biomass at the next level
- > carnivores are larger at successive trophic levels - Stability requirements
- > fluctuations at lower trophic levels are magnified at higher levels