Community Assembly Flashcards
How are communities structured?
via both direct and indirect species interactions
What is trophic cascade?
indirect interaction in which predator of a predator (or herbivore) benefits the producer indirectly
- direct interactions in trophic cascade are the negative predator-prey interactions
- indirect interaction is positive impact of carnivore on producer by consuming sea urchin
What is trophic facilitation?
indirect effect in which one species benefits another via a positive interaction (mutualism)
Ecological networks are…
a set of ecological interactions within a community
What do food webs summarize?
feeding relationships in a community
Levels of food webs
- level 1: primary producers (plants and algae)
- level 2: herbivores (heterotrophes - insects and mites)
- level 3 and above: predators (heterotrophes - birds, mammals, spiders etc.)
What are Guilds?
- are a group of species that exploit the same resources in related ways
- feed on organisms in across trophic levels
Limitation of food webs?
while a food web illustrates the complexity of interactions among species in different trophic levels it does not reveal the abundance of specific trophic levels
What do Biomass Pyramids represent?
illustration of abundance at various trophic levels
What is a Keystone?
- an organism that defines the entire ecosystem
- these species have low functional redundancy
- if they disappear, no other species are able to fill their ecological niche
Keystone predator species keep the numbers of prey populations below K, and thus…
- decrease competition
- create ecological niches
- increase diversity within communities
Difference between Keystone and Dominant species?
keystone species have a high impact DESPITE having a low abundance
- aka a disproportionate impact relative to their population size
How do Predators increase diversity?
- as the number of species in his inter intertidal food webs increased, the proportion of the web represented by predators also increased
- as the number of predator species in a community increased, the local species diversity increased
Do predators directly influence species diversity (Paine experiment)
- paine experimentally removed top predatory from temperate intertidal food web and monitored response over 2 years
- removal of starfish (top predator) caused decline in diversity from 15-8 species
- appears competition is for space
Example of Keystones in Conservation Efforts
- after wolves disappeared from Yellowstone National part in the mid-1900’s, elk populations exploded
- elk eat a lot of plants, including young seedlings and willows which grow along riverbanks
- the roots of these plants hold soil in place and their disappearance led to massive erosion, destroying habitats for beavers and birds among others
What are the requirements for keystone status is
- have relatively low biomass in the community
- high impact on community structure
Example of Non-predator keystone species
- argentine ants, a species that does not disperse seeds, invaded shrublands of the fynbos of south africa
- they displaced native ant species that were known to disperse large seeds, but small- seed-disperser ants were largely unaffected
Umbrella Species
- species that are selected as representatives of their ecosystem when conservation plans are being made
- protection of umbrella species will protect a large amount of co-occurring species, as their home ranges overlap
- this is a way to made as large of an impact as possible, using the least amount of resources
- these can be keystones, but do not have to be
Ecosystem Engineers
- differ in type of impact, are not essential due to their trophic effect
- their abundance does not need to be high to have an impact on the ecosystem
What are the two types of ecosystem engineers?
- allogenic - modify the environment by mechanically changing the living/non living material from one form to another
- autogenic - modify the environment by modifying themselves
Beavers as ecosystem engineers
- beavers cut down trees near streams, forming dams
- dams cause flooding, formation of ponds and increased riparian area
- beavers build lodges in resulting ponds
- major impacts on both stream and surrounding terrestrial area
What is the key difference between a dominant, foundational species vs. a keystone species?
dominant species are the most abundant species, whereas keystones exert control over a community via important roles/niches
