Community Ecology Flashcards by Ateeya Cali

A community’s structure can be described by its

species richness

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the number of species present

species richness

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is a measure of both species richness and species evenness (relative numbers)

species diversity

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Community structure is influenced by many factors, including:

abiotic factors, species interactions, level of disturbance, and chance events.

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play particularly important roles in determining their communities’

foundation species and keystone species

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is the feeding relationships between organisms in a community
It is a key factor in community dynamics

Trophic structure

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link trophic levels from producers to top carnivores

Food chains

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is a branching food chain with complex trophic interactions

Foods Webs

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Food webs can be simplified by

Grouping species with similar trophic relationships into broad functional groups
Isolating a portion of a community that interacts very little with the rest of the community

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Each food chain in a food web is usually only

a few links long

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Two hypotheses attempt to explain food chain length

the energetic hypothesis and the dynamic stability hypothesis

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suggests that length is limited by inefficient energy transfer.

For example, a producer level consisting of 100 kg of plant material can support about 10 kg of herbivore biomass.

energetic hypothesis

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the total mass of all individuals in a population

biomass

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proposes that long food chains are less stable than short ones

dynamic stability hypothesis

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Most data support the _______ hypothesis

energetic hypothesis

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highly abundant or play a pivotal role in community dynamics

Species with a Large Impact

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are those that are most abundant or have the highest biomass

Dominant Species

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_______ exert powerful control over the occurrence and distribution of other species

For example, _______ have a major impact on shading and soil nutrient availability in eastern North America; this affects the distribution of other plant species

Dominant Species; sugar maples

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One hypothesis suggests that ______ are most competitive in exploiting resources

Another hypothesis is that ______ are most successful at avoiding predators

dominant species

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typically introduced to a new environment by humans, often lack predators or disease

Invasive species

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exert strong control on a community by their ecological roles, or niches

Keystone Species

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In contrast to dominant species, they are not necessarily abundant in a community

Keystone Species

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Field studies of _____ illustrate their role as a keystone species in intertidal communities

sea stars

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Is an event that changes a community

Removes organisms from a community

Alters resource availability

A disturbance

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Is a significant disturbance in most terrestrial ecosystems Is often a necessity in some communities

Fire disturbance

Suggests that moderate levels of disturbance can foster higher species diversity than low levels of disturbance

The intermediate disturbance hypothesis

Demonstrated that communities can often respond very rapidly to a massive disturbance

The large-scale fire in Yellowstone National Park in 1988

Are the most widespread agents of disturbance

Humans

Usually reduces species diversity

Human disturbance to communities

also prevent some naturally occurring disturbances. Which can be important to community structure

Humans

Is the sequence of community and ecosystem changes after a disturbance

Ecological succession

Occurs where no soil exists when succession begins

Primary succession

Begins in an area where soil remains after a disturbance

Secondary succession

May facilitate the appearance of later species by making the environment more favorable May inhibit establishment of later species May tolerate later species but have no impact on their establishment

Early-arriving species

Provide a valuable field-research opportunity on succession

Retreating glaciers

Follows a predictable pattern of change in vegetation and soil characteristics

Succession on the moraines in Glacier Bay, Alaska A. Pioneer stage, with fireweed dominant B. Dryas stage C. Spruce stage D. Nitrogen fixation by Dryas and alder increases the soil nitrogen content.

Biogeographic factors affect

community diversity

Two key factors correlated with a community’s species diversity are

its geographic location and its size

The two key factors in equatorial-polar gradients of species richness

Are probably evolutionary history and climate

generally declines along an equatorial-polar gradient And is especially great in the tropics

Species richness

May account for the greater species richness

The greater age of tropical environments

Is likely the primary cause of the latitudinal gradient in biodiversity

Climate

The two main climatic factors correlated with biodiversity

Are solar energy input and water availability

quantifies the idea that all other factors being equal, the larger the geographic area of a community, the greater the number of species. A ________ supports this idea

species-area curve; species-area curve of North American breeding birds

Habitat and Niche Key Concept:

Every organism has a habitat and a niche.

differs from a niche. is all aspects of the area in which an organism lives. (biotic factors and abiotic factors)

habitat

includes all of the factors that a species needs to survive, stay healthy, and reproduce. (food, abiotic conditions, behavior)

ecological niche

Resource availability gives structure to a

community

Species can share

habitats and resources

occurs when two species use resources in the same way.

competition

keeps two species from occupying the same niche.

Competitive exclusion

different outcomes of competitive exclusion

One species is better suited to the niche and the other will either be pushed out or become extinct. The niche will be divided. The two species will further diverge.

are species that occupy similar niches but live in different geographical regions.

Ecological equivalents

is the variety of organisms that make up the community

Species diversity of a community

two components of species diversity

species richness and relative abundance (Two communities can have the same species richness but a different relative abundance )

is the total number of different species in the community

Species richness

is the proportion each species represents of the total individuals in the community

Relative abundance

Diversity can be compared using a

diversity index

H = – (pA ln pA + pB ln pB + pC ln pC + …) where A, B, C . . . are the species, p is the relative abundance of each species, and ln is the natural logarithm

Shannon diversity index (H)

Determining the number and abundance of species in a community is ____, especially for small organisms

difficult

can be used to help determine microbial diversity

Molecular tools

Ecologists manipulate diversity in experimental communities to study the _______. For example, plant diversity has been manipulated at _______________.

potential benefits of diversity; Cedar Creek Natural History Area in Minnesota for two decades

Communities with higher diversity are

More productive and more stable in their productivity Better able to withstand and recover from environmental stresses More resistant to invasive specie

organisms that become established outside their native range

invasive species

Ecological Succession Key Concept:

Ecological succession is a process of change in the species that make up a community.

occurs following a disturbance in an ecosystem. regenerates or creates a community after a disturbance. - a sequence of biotic changes - damaged communities are regenerated - new communities arise in previously uninhabited areas

Succession

two types of succession.

primary succession secondary succession

started by pioneer species

primary succession

started by remaining species

secondary succession

or secondary natural succession

AUTOREGENERATION

example of secondary natural succession of pioneer species on a land that was cleared from less than five years

Alim (Mallotus multiglandulosus), Aratiles (Multingiacalabura), Binunga (Macaranga tanarius), Anabiong (Trema orientalis) Hagonoy (Euphatorium odoratum) Cogon grass

Why does change or succession occur?

It occurs as the result of either autogenic processes (associated with the living community) or allogenic processes (associated with the physical environment).

result of three major biotic mechanisms

Autogenic succession

three major biotic mechanisms

1. Colonization 2. Alteration of the physical characteristics of the site 3. Displacement of species by competition or antibiosis.