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Field Ecology
BIO 112 Intro. to Ecology
Summer 2015 (McDill)
Overview
Disturbance and Succession
Ecology is the study of the interaction of organisms with their physical
environment and with each other. Ecologists try to discover how an
organism affects, and is affected by, the biotic (living) and abiotic
(nonliving) factors in its environment. They are also interested in
knowing how these interactions determine the numbers and kinds of
organisms found in a particular place at a particular time. Indeed, one
alternative definition of ecology is “the study of why organisms live
where they do.” Ecologists conduct their investigations both in the field
and in the laboratory, and the data obtained from their investigations are
both qualitative and quantitative.
Communities change over time. Some
changes are in response to external natural
forces, including long-term climatic changes,
geological changes, and catastrophic events
such as fire, drought, or hurricane (or a
bulldozer being driven through a field).
Sudden changes are sometimes characterized
as “disturbance.”
Other changes may be due to the growth
of organisms. For example, the growth of
pioneer plant species may make conditions
more suitable for non-pioneer species. Aspen
trees may give way to spruce; annual forbs
(herbaceous plants that are not grasses) may
give way to prairie grass. This progressive
change in community composition or
vegetation type (e.g. meadow to woodland to
forest) is referred to as ecological succession.
Disturbance often sets the stage for succession
to occur.
Long before the word “ecology” was coined, there was a tradition of
observation and enjoyment of organisms in their natural environment.
For people of early hunting-and-gathering cultures, survival depended on
good observations. The intense interest in observing firsthand the world’s
organisms and their environments led early plant geographers and
naturalists, including Alexander von Humboldt and Charles Darwin, on
incredible journeys that greatly increased our understanding of the
natural world. A qualitative description of the Danube River basin by A.
von Marilaun Kerner (1865) is often considered to be the first ecological
work.
The term population refers to all members of the same species within an
area. The biotic community is the assemblage of interacting populations of
different species that inhabit the same general environment. The biotic
community and the physical factors of the environment interact as a
dynamic ecological system, or ecosystem.
Is there any evidence of disturbance or
succession at any of the sites we visit?
By the end of the course, you will have visited several contrasting
ecosystems. Your field notes should include information provided by
the trip leader as well as your own observations. Qualitative (descriptive)
observations provide ecological insights and often precede the
formulation of hypotheses that are tested quantitatively (i.e. through
analysis of numerical data).
Qualitative Observations in the Field
For each terrestrial ecosystem, such as the oak woodlands, chaparral,
and tidal marsh, make observations of the biotic community in relation
to its physical environment; interactions between organisms; and any
evidence of change in the communities.
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The Biotic Community and its Physical Environment
After the trip…
Physical Environment
1. At each site, record your general observations of the steepness and
direction of the slope, exposure to prevailing winds, light intensity
air and soil moisture, and temperature.
Organize the data (your observations)
under ecological categories. The following
may serve as guidelines. You may want to
add additional categories or organize things
differently.
2.
3.
Note general soil characteristics, such as very sandy texture,
bedrock near the surface, and poor drainage.
Estimate the leaf-litter depth.
The Biotic Community
4. Using biomass (bulk) as the criterion for dominance, identify the
plant forms that seem to dominate the community
5.
Are there different layers, or vertical structure, in the area/habitat—
for example, a canopy, an understory, and a groundcover layer?
6.
Are the abiotic factors the same in each layer?
7.
What plant forms are most typical of each layer?
8.
With the help of your instructor and/or any field guides brought
along, identify some of the plant species in each layer and discuss
some of the ways in which these plants are adapted to their
environment.
9.
1.
Finally, review your observations and relate the community at each
site to its physical environment.
10. In what ways have specific physical factors limited and determined
the plant life of the communities?
2.
3.
4.
5.
Food webs or Trophic Level (flow of
energy and nutrients)
a. Herbivory
b. Predation
c. Decomposition
Symbioses
a. Mutualism
b. Parasitism
c. Commensalism
Competition
a. Interspecific
b. Intraspecific
Habitat Structural Features
a. Food source
b. Water source
c. Protection/cover
d. Den/nest sites
Modification of Environment
a. Leaf litter
b. Shade
c. Soil compaction
d. Etc.
11. As you explore each community, record any evidence you see of
interactions between two plants, between two animals, or between a
plant and an animal. For example, note the pattern of holes in a
leaf, the presence of a bird nest in a bush, a bee on a flower, moss or
lichen on a log, and any droppings or other physical evidence
(flattened grass) of an animal’s passing. Note also any plant
adaptations that may discourage or encourage interactions (such as
spines to prevent herbivory).
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