module 13 Flashcards
Community
Association of interacting species inhabiting some defined area.
Community Structure
Includes attributes such as:
Number of species
Relative species abundance
Species diversity
Guild
Group of organisms that all make their living in the same fashion.
Seed eating animals in the desert.
Life Form
grouped together based on Combination of structure and growth dynamics.
How Diverse Is the World?
2 million Species Identified
As Many as 30 Million plants & Animals
Many more Bacterial Species
Biodiversity
The Variety of types of organisms, habitats, and ecosystems on earth or in a particular place
- Genetic Diversity-natural selection, how many different ales, genes
- Species, Genera, or Family Diversity
- Ecosystem Diversity-various diff habitats
Diversity in Geologic Time
background extinctions
mass extinctions
times of tremendous radiation of taxa
Constant Species Turnover
- Background Extinctions-every species has extinct or will go extinct in the future, extinction is normal
- Mass Extinctions-loosing large portion of species found in the world
- Times of Tremendous Radiation of Taxa-when one group declines other increases, radiate out and fill niches
Latitudinal Gradients in Diversity-diversity increases in
Diversity increases with lower latitudes
Especially within Taxa
Species Diversity in US
mammals
avian species
reptiles and amphibians
-Mammals More Diverse in West -Avian Species Similar Pattern -Reptiles & Amphibians More Diverse in East
Habitat & Physical Conditions
Variation Occurs within Regions
more diverse=
Variation Occurs within Regions Habitat Structure Heterogeneity of Habitat Variation in Primary Production more variations more heterogenous
relative abundance
Relative Abundance
- Number of Individuals of a Species as a percentage of individuals of all Species
- Regularities in the relative abundance of species in communities that hold regardless of the ecosystem.
Relative Abundance
Few species are
exaggerated by
Few species are abundant
Most species Relatively Rare
-Small portion of biomass or # of individuals
-Exaggerated by Sampling effect
Dominants
generally through
The few species that attain high abundances in a community
Generally through superior Competition
Lognormal Model-veil line
portion of lognormal curve is
Veil Line
Portion of Lognormal Curve < 1
Suggests species exist that were not sampled
Two factors define species diversity:
Species Richness
Number of species in the community.
Species Evenness
Relative abundance of species- how they are spread out.
Dominants influence
- Single or few species that predominates within community
- Exert Strong influence based on their abundance
Abundance alone not always a sufficient measure of dominance
Most numerous may not have most biomass
Virginia deciduous forest Red maple and dogwood 60% relative abundance White Oaks 60% biomass, only 9% relative abundance -also look at biomass
Keystone Species, role of keystone species, removal of keystone species can lead to
Species with low abundance/biomass in community
- Exerts strong effects on structure of community
- Often more than would be expected from its abundance
Role of a keystone species
- create or modify habitats
- influence interactions among other species
Removal of a keystone species can lead to
- changes in community structure
- loss of biodiversity
Diversity & Community Functioning
starfish
Species Composition Influenced by Complex Interactions
-Predation often affects competitive interactions
Rocky intertidal zone of the Pacific Northwest
- Many invertebrate herbivores
- —mussels, barnacles, limpets, chitons
- Starfish prey on all of these groups
starfish lessen the effects of competition and exclusion allow diversity to stay high
Keystone Species: Summation
Keystone species
Exert strong effects on their community structure
Despite low biomass
Function by altering interactions
Dominant Species
Exert strong effects on community structure
Large Biomass
Function through competition
Food chain
representation of feeding relationships within a community
Descriptive diagram of flow of energy from prey to predator
Food web
Representation of complex interactions of predators and prey
Primary producers form base of the food web
Food Webs and Productivity
Trophic Level determined by:
Position determined by # of energy transfers
-from primary producers to current level:
Primary producers
-First level.
Primary consumers
Secondary consumers
Tertiary consumers
types of Control of Primary Production
Bottom-up Controls
-Physical and Chemical factors that influence Primary Production
—Lower Trophic levels Control Higher
—Ecosystem Function
Terrestrial Environments
-Temperature and Moisture
Aquatic Environments
-Nutrients Availability
—Phosphorous in Freshwater; Nitrogen in Saltwater
Top Down Controls
-Consumers May Influence Primary Production
Carpenter
Proposed piscivores and planktivorous fish can cause significant deviations in primary productivity.
Carpenter and Kitchell
came up with what hypothesis
Proposed the influence of consumers on lake primary productivity propagate through food webs.
Trophic Cascade Hypothesis
top-down effects
largest in
impact less when
Top-Down Effects
- Trophic Cascade
- Largest in low Diversity Systems
- Impact Less when:
- –Choices in Food Items Increases
- –Specialization of Upper Trophic Levels Increase
- –Stabilizes System
Environmental Complexity
-species diversity increases when environmental complexity or heterogeneity
MacArthur
in general:
-Species diversity increases with environmental complexity or heterogeneity.
MacArthur
—Environmental complexity = foliage height.
—Warbler diversity increased as vegetation stature increased.
-Many studies have shown positive relationship between environmental complexity and species diversity.
–Environmental Complexity ->
More Habitats
More Habitat Space
Niches and Diversity of Algae and Plants
-why is there coexistence?
- Hutchinson:
- Phytoplankton communities
- -Present a paradox
- —Live in relatively simple environments
- —Compete for the same nutrients
- —Yet many species coexist without competitive exclusion.
- Environmental complexity may account for significant portion of the diversity.
algal niches
Algal niches
- Appear to be defined by small shifts in balance of nutrient requirements.
- Tilman found:
- –Coexistence of freshwater diatoms depended upon ratio of silicate and phosphate.
- -Found conditions allowing coexistence.
- —–Diatoms held different trophic niches.
- —-Thus different diatoms would dominate different areas.
Diversity & Primary Production
Production ->More Energy -> More Species?
Sometimes True
May be Correlated
Not Determinant
Algal & Plant Diversity & Increased Nutrient Availability
-adding nutrients to water or soils ____ diversity and ____competition
- Nutrient availability & Diversity
- –Negative relationship
- –Adding nutrients to water or soils
- —-Generally reduces diversity of plants and algae.
- —-Reduces number of limiting nutrients
- ——–Increases Competition
Paradox of Enrichment
production and diversity are often ____ correlated
Diversity & Production often negatively Correlated
-Habitat Heterogeneity
Monocultures often most Productive
Dominant Species Extremely successful
Disturbance
Difficult to define
Involves departure from “average conditions.”
Average conditions may involve substantial variation.
Sousa defined disturbance:
Discrete, punctuated, killing, displacement, or damaging of one or more individuals that directly or indirectly creates an opportunity for new individuals to be established.
Disturbance and Diversity
white and Pickett
two major characteristics
White and Pickett defined disturbance: -Any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment. -Two major characteristics: Frequency Intensity
Intermediate Disturbance Hypothesis
Connell
- Disturbance is a prevalent feature that significantly influences community diversity.
- Both high and low levels of disturbance would reduce diversity.
- Intermediate levels promote higher diversity.
- –Sufficient time between disturbances:
- —–Allows wide variety of species to colonize
- —–But not long enough to allow competitive exclusion.
Dynamic Equilibrium Model
Interaction between the extent of disturbance in a community and the rates of population growth of species in the community determines diversity
