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44.1 Communities Contain Species That · PDF file •Example: On Krakatau, tropical forests eventually came back. But return of the original community is not guaranteed. Concept 44.2

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  • Ecological Communities

    44

  • Chapter 44 Ecological Communities

    Key Concepts

    44.1 Communities Contain Species That

    Colonize and Persist

    44.2 Communities Change over Space and Time

    44.3 Community Structure Affects Community

    Function

    44.4 Diversity Patterns Provide Clues to What

    Determines Diversity

    44.5 Community Ecology Suggests Strategies

    for Conserving Community Function

  • Chapter 44 Opening Question

    Can we use principles of community ecology to improve methods of coffee cultivation?

  • Concept 44.1 Communities Contain Species That Colonize and

    Persist

    Community: group of species that occur

    together in a geographic area

    We depend on communities for natural

    resources and services.

    A community’s species and their interactions

    determine how well it functions.

    Understanding how communities are put

    together and how they work is essential to

    conserving them.

  • Concept 44.1 Communities Contain Species That Colonize and

    Persist

    Ecologists must make practical decisions on the

    boundaries of the community under study.

    Boundaries may be based on natural

    boundaries (e.g., the edge of a pond).

    They may restrict study to certain groups (e.g.,

    the bird community) or study a representative

    portion of a habitat.

  • Concept 44.1 Communities Contain Species That Colonize and

    Persist

    Communities are characterized by species

    composition—which species they contain,

    the number of species, and the abundance of

    each species.

    These attributes are components of the

    community structure.

  • Concept 44.1 Communities Contain Species That Colonize and

    Persist

    A species can occur in a location only if it is

    able to colonize and persist there.

    A community contains those species that have

    colonized minus those that have gone extinct

    locally.

    Species may fail to colonize a community, or be

    lost from it, for many reasons.

  • Concept 44.1 Communities Contain Species That Colonize and

    Persist

    Local extinctions can occur for many reasons:

    • Inability of species to tolerate local

    conditions

    • A resource may be lacking

    • Exclusion by competitors, predators, or

    pathogens

    • Population size too small; no reproduction

  • Concept 44.1 Communities Contain Species That Colonize and

    Persist

    In 1883 the volcano on Krakatau in Indonesia

    erupted, killing everything on the island.

    Scientists studied the return of living organisms.

    Within 3 years, seeds of 24 plant species had

    reached the island.

    Later, as trees grew up, some early pioneer

    plant species that require high light levels

    disappeared from the island’s now-shady

    interior.

  • Concept 44.1 Communities Contain Species That Colonize and

    Persist

    Once forests developed, fruit-eating birds and

    bats were attracted to the island, bringing new

    animal-dispersed seeds with them.

    Even today, species composition continues to

    change as new species colonize and others

    go extinct.

  • Figure 44.1 Vegetation Recolonized Krakatau

  • Concept 44.2 Communities Change over Space and Time

    Ecologists have noted repeated patterns of

    spatial and temporal change, or turnover, in

    species composition of communities.

    Species composition varies along

    environmental gradients, after disturbances,

    and with changing climate.

  • Concept 44.2 Communities Change over Space and Time

    Species composition changes along

    environmental gradients, such as elevation or

    soil types.

    • Example: As you go up a tropical mountain,

    there are gradients in temperature and

    moisture; because different species have

    different tolerance limits, there are

    constantly changing plant communities.

  • Concept 44.2 Communities Change over Space and Time

    Change in plant species composition was

    measured along a transect (a straight line

    used for ecological surveys) running from non-

    serpentine to serpentine soils.

    The turnover of plant species along the transect

    reflects their tolerance or intolerance to the

    heavy metals that characterize serpentine

    soils.

  • Figure 44.2 Change in Species Composition along an Environmental Gradient

  • Concept 44.2 Communities Change over Space and Time

    Many animal species are associated with

    particular plant communities:

    • Plants they eat may be there

    • Plants modify physical conditions,

    contributing to habitat structure

    Morphological, physiological, and behavioral

    traits of animals adapt them for the structure

    of the habitats with which they are associated.

  • Figure 44.3 Many Animals Are Associated with Habitats of a Particular Structure

  • Concept 44.2 Communities Change over Space and Time

    Species composition also changes over time.

    All communities are dynamic.

    There is ongoing colonization and local

    extinction and thus a steady turnover in

    species composition.

    Dispersal delivers a constant influx of new

    individuals to all but the most isolated

    locations.

  • Concept 44.2 Communities Change over Space and Time

    Disturbance—events that cause sudden

    environmental change can change species

    composition

    Disturbances include volcanic eruptions,

    wildfires, hurricanes, landslides, human

    activities.

    Some or all species are wiped out, and

    environmental conditions are changed.

  • Concept 44.2 Communities Change over Space and Time

    New environments can also appear without

    disturbance; for instance, when a glacier melts

    away, a depression fills with rainwater, or a

    mammal deposits dung.

    Species often replace one another in a

    predictable sequence called succession.

    • Example: A patch of elephant dung is

    colonized by a series of dung beetle

    species.

  • Figure 44.4 Dung Beetle Species Composition Changes over Time

  • Figure 44.4 Dung Beetle Species Composition Changes over Time (Part 1)

  • Figure 44.4 Dung Beetle Species Composition Changes over Time (Part 2)

  • Concept 44.2 Communities Change over Space and Time

    Factors that result in successional sequences:

    • Some species are better at colonizing than

    others.

     Early-arriving dung beetles tend to be

    strong fliers with a good sense of smell,

    or “hitchhikers” that ride on the dung-

    producers.

     On Krakatau, the first plants were

    species that have seeds that are easily

    dispersed by sea or wind.

  • Concept 44.2 Communities Change over Space and Time

    • After a disturbance, environmental

    conditions change with time.

     Dung starts out wet and dries over time.

     As trees grow, the forest canopy closes

    and light conditions change.

  • Concept 44.2 Communities Change over Space and Time

    After a disturbance, succession often leads to a

    community that resembles the original one.

    • Example: On Krakatau, tropical forests

    eventually came back.

    But return of the original community is not

    guaranteed.

  • Concept 44.2 Communities Change over Space and Time

    Some disturbances may push the system past a

    threshold, or tipping point, causing an

    ecological transition to a distinctly different

    community.

    • Example: conversion of grasslands to

    shrublands in the U.S.–Mexico Borderlands

    after intensive cattle grazing

  • Concept 44.2 Communities Change over Space and Time

    Climate change can also cause temporal

    variation in communities.

    As physical conditions change, the geographic

    ranges of species necessarily change with

    them.

  • Concept 44.2 Communities Change over Space and Time

    One way to reconstruct such change is analysis

    of fossilized plant remains in packrat middens.

    Biologists can show how plant communities of

    the Borderlands changed over the last 14,000

    years as the climate became drier.

  • Figure 44.5 Species Composition Changes as the Climate Changes

  • Concept 44.3 Community Structure Affects Community Function

    An ecological community can be thought of as a

    system with inputs, “internal workings,” and

    outputs.

    Inputs include energy and materials from the

    abiotic environment.

    Internal workings include the metabolism of its

    individuals, dynamics of its populations, and

    interactions among species.

    Outputs are transforme

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