LE 9: Communities Flashcards
What are communities?
A group of different populations that interact with each other in the same place at the same time.
What is the difference between a biome and a community?
Biome: abiotic conditions that predict the type of organisms
Community: specific species who interact, how they interact, etc.
- food webs, predators, competitors, etc.
What hypotheses support why communities are the way they are? Which one(s) is/are true?
Interdependence hypothesis: organisms in a community rely on each other, affecting why they live in the same place
- similar needs and high competition leads to more interdependence
Similar needs hypothesis: organisms have similar needs for abiotic factors resulting them in living in the same place
- ≠ need each other but they need similar resources/abiotic factors
Both are valid as changes are based on ecological conditions:
- effects of neighbors = interdependence
- low elevations = survive better + vice versa
- effects of neighbors on fitness = interdependence
- low effects = do better
What are niches and its relation to organization in communities?
In each biome, certain species fill a particular niche/role.
What is convergent evolution?
Similar biomes have different communities with species that fill in similar niches
How do abiotic factors determine the distribution of species?
Moisture gradients affects where trees will be placed over a space and influences what species can live there.
Ecotone: distinct boundary of a distribution of species; where species can exist within
- example: edge of a forest
Ecological succession: process of when communities change over time naturally
- example: different plants are needed in order for a forest to grow
Some species can draw in other species (interdependence)
- bare land brings in grasshoppers which brings in sparrows which brings in grassland, etc etc
Community structure is determined by both biotic and abiotic factors
- example: barnacles live on different height sin intertidal zones based on how tolerable they are against predators
What are trophic levels and the regulations involved?
Trophic levels are the different levels of species in a community.
Top-down regulation: layer above affects the layers below
- example: fewer top predators, fewer secondary consumers, fewer primary consumers, etc.
Bottom-up regulation: layer below affects the layers above
- example: fewer producers. fewer primary consumers, fewer secondary consumers, fewer predators
What is biodiversity and how is it measured?
The variety of life in a particular habitat that is measured by:
- richness: total # of species, S; the more abundance, the higher the richness
- evenness: how evenly represented each species is; more evenness = flatter zero slope
What is Shannon’s index and when is it used?
It is an information statistic index that measure biodiversity when the assumptions that all species are represented and random sampling has been met
Minimum value: 0 (when there is only one species)
Maximum value: ln(# of species); all species have the same relative abundance
What Simpson’s Biodiversity index?
It is a dominance index that measures biodiversity, where more dominant species affect the index more greatly and when species with less individuals do not affect diversity much.
Minimum value: 0
Maximum value: 1 (all species have the same relative abundance)
What are the different interspecific interactions?
Conspecific: within the same species
Inter/heterospecific: between 2 different species
What are keystone species and their effects on biodiversity?
A species whose removal leads to major and disproportionate changes in the diversity and density of associated species
Example: kangaroo rats make burrows
- shelters squirrels and lizards + increases mobility for insects
- stashing seeds increases seed dispersal and diversity
- prey for foxes
What questions are asked about a community?
How does this factor change the structure of a community?
How does this factor change the richness of a community?
How does the presence/absence of this species affect this organism?
How does the structure/richness/diversity of this community change over space/time?
