Transcript Communities - Bird Conservation Research, Inc.

Communities
Definition:
Community- a
collection of
species living
in the same
area that may
interact.
The Ecological Niche
•
•
Niche- the range of conditions (ecological amplitude) tolerated (or preferred)
by species within a community; a hypervolume (like a graph with more than
three dimensions).
By graphing the range of conditions over which a species occurs, we gain an
understanding of the species’ niche.
The graph below shows the Blue-gray Gnatcatcher with respect to two
dimensions: populations and forest type; populations are greatest in deciduous
forests and are absent from conifer forests.
Blue-gray Gnatcatcher
Density (males/100 ha)
•
50
1 = deciduous 2 =
mixed 3 = conifer
40
30
20
10
0
1
1.5
2
Forest Type
2.5
Communities and Niches
• Within communities, species
have different niches (they use
habitats differently).
• Example: the Red-eyed Vireo
(above) lives in interior
forests, and the Warbling
Vireo (below) uses forest
edges.
• By having different niches,
species subdivide the habitat
among them.
• Subdivision can occur over
living space or food.
Community
RelationshipsConsidering Two
Dimensions
• Species and communities are
influenced by a variety of habitat
factors.
• In the adjacent graphs, species
richness in a bird community is
related to a measure of local
temperature.
• What is the relationship of
temperature (larger values are
associated with lower local
temperatures) to species richness
in summer vs. winter?
Community Relationships- Considering
Three or More Dimensions
• Species within
communities are influenced
by more than one factor
simultaneously, and threedimensional graphs
illustrate this.
• In the adjacent graph, bird
species richness is
influenced not only to
season but also geographic
region (northeastern vs.
southeastern Connecticut).
• How does the relationship
of species richness to
season change between
regions?
Community Interactions
• Competition- negative interactions between species
(interspecific competition) or within species (intraspecific
competition). Example: competition for food and living
space.
• Predation- organisms that feed on other organisms.
Herbivores feed on plants, carnivores feed on animals, and
detritivores feed on the remains of organisms.
• Symbiosis- interactions between organisms that are
beneficial. Example: mutualism occurs when both
interacting organisms benefit.
• Allelopathy- the occurrence of one species can “poison” a
habitat for other species.
Environmental Gradients
• As habitat conditions change, the species present change (species with
different ecological niches appear) , leading to the development of different
communities.
• Example: a forested slope in southern New England:
Community Development
• The process of community
development over time is
called succession. There
are two types.
• Primary succession- the
developmental sequence
that follows initial
colonization of mineral
substrates by living
organisms.
• Secondary succession- the
sequence that occurs
following disturbance of a
pre-existing community.
Definitions
Seral stage- a recognizable stage in a successional sequence.
Climax community- that stage at which a community reaches
a steady state (above left).
Types of primary succession:
1. Xerarch- succession in uplands (above right- the dark
gray soil was deposited during an ancient glaciation and
the lighter soil above it was deposited after the most recent
glaciation, about 17,000 years ago).
2. Hydrarch- succession in wetlands (below right- in bog).
Primary Succession
• After glacial times, the landscape of
southern New England was colonized
first by, small, primitive plant-like forms.
• These forms changed their environment,
and were then succeeded by herbaceous
plants and trees over a period of roughly
10,000 years (below).
• Some peaks in the Berkshire Mts. (right)
have been in early to mid-succession for
thousands of years.
Secondary Succession
• After the early 1800s, much farmland in
southern New England was abandoned.
• Bare mineral soil was first colonized by
annual weeds, which were then replaced by
perennial herbs within 1-2 years.
• After 5-10 years, woody plants invade the
meadow, thereby becoming an old field.
• After about 25 years, the canopy of the old
field closes into a young forest.
• After 50 years, the forest matures, and by
150 years an old growth forest develops.
Factors Influencing
Succession
• Disturbance, such as through animal
activity, fire, agriculture, logging.
• Previous land use (e.g. land once used
as a pasture will develop differently
than land used as a cornfield). Note
the wide growth form of the tree at
left that began growing when the area
was a pasture.
• The nature of surrounding habitats
(e.g. an adjacent forest provides seeds
that can germinate in an old field).
Setting Back
Succession
• Before (left)- the volcano of Anatahan Island
as it was in 1990. Note that vegetation is
present to the bottom of the crater.
• After (above)- a massive eruption in 2004
eliminated all vegetation, bringing the island
back to a bare mineral state in which primary
succession was again initiated.