module 13 Flashcards by Amanda Salinas

Community

Association of interacting species inhabiting some defined area.

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Community Structure

Includes attributes such as:

Number of species
Relative species abundance
Species diversity

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Guild

Group of organisms that all make their living in the same fashion.
Seed eating animals in the desert.

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Life Form

grouped together based on Combination of structure and growth dynamics.

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How Diverse Is the World?

2 million Species Identified
As Many as 30 Million plants & Animals
Many more Bacterial Species

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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

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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

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Latitudinal Gradients in Diversity-diversity increases in

Diversity increases with lower latitudes

Especially within Taxa

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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

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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

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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.

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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

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Dominants

generally through

The few species that attain high abundances in a community

Generally through superior Competition

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Lognormal Model-veil line

portion of lognormal curve is

Veil Line
Portion of Lognormal Curve < 1
Suggests species exist that were not sampled

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Two factors define species diversity:

Species Richness
Number of species in the community.

Species Evenness
Relative abundance of species- how they are spread out.

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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

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module 13 Flashcards

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