BSCI 124 Lecture Notes
Undergraduate Program in Plant Biology, University of Maryland
LECTURE 33 - ECOLOGY
I. Important terms
A. Ecology is a very complex field of study involving the effects of the
environment on living organisms, the effects of living organisms on the
environment, and the effects that living organisms have on one another.
II. Plant community
B. Plant ecology is the study of the interaction
among plants, and between plants and their environment.
C. Population- all the members of a single species that live together
1. Understanding these relationships is important for those who grow crops,
provide lumber, raise cattle, protect endangered species or threatened
ecosystems, and for any concerned citizen. How life functions is one of
the most fundamental questions for humans throughout history.
a. involves energy flow from the sun through organisms
b. involves cycling of matter
c. involves species diversity and their interactions
1. For example, an ecologist might investigate a population of ponderosa
pine trees (Pinus ponderosa) by examining both its physiology
and its habitat
(the location where the population is found).
A plant community consists of different populations of plants living
together in the same geographic area.
A. Plant communities are usually defined by the dominant species, such
as the white pine forest community. The dominant species are the most influential
species in the community.
B. They control the structure, and to some degree, the species composition
of the community through their effects on the physical and chemical factors
in the community including:
C. Within each plant community may be a variety of plant forms, such as
trees, shrubs, and a plant ground cover.
1. light (provide shade)
2. wind (wind screen)
3. humidity (higher than in open areas)
4. availability of water and nutrients in the soils
1. a tree
is a woody plant that generally has a single stem (trunk)
2. a relatively small woody plant typically with several stems arising
near the ground is called a shrub
3. the ground
cover may consist grasses or forbs. A forb is any small herbaceous
(no wood) plant that is not a grass. Some or all of the ground may not
be covered by plants. There may be bare ground or sand. In some forest
communities, the ground may be covered by litter, a layer of slightly decomposed
Ecosystem- a community with all its living organisms (biotic) and its
nonliving environment (abiotic).
A. A plant community exists in a particular habitat created by all the
biotic and abiotic factors. Every plant species has a range of environmental
conditions that it can tolerate. Some plant species can live only in dry
soil and others in wet,
some in bright light
and others in shade,
some in hot climates
and others in cold.
The plants that live within a community are able to tolerate the various
environmental factors that make up that community's habitat.
B. Biotic - There are many more organisms that live in a community
besides the plants. The community supports a variety of animals including
1. organisms interact and form a food chain
2. dead material in the community is decomposed
by fungi (such as mushrooms) and soil bacteria
a. the organisms that obtain their energy from the sun through the process
of photosynthesis are called primary producers
b. animals that eat the primary producers are called herbivores
or 1st order consumers
c. animals that eat the 1st order consumers are called carnivores
or 2nd order consumers, and so on
1. climate - Temperate climates with generally moderate temperatures and
significant rainfall, such as that found in the eastern United States,
permit extensive plant growth.
2. light - The availability of affects plant composition in the communities;
plants requiring strong
sunlight cannot grow in the dark understory of the summer forest; other
plants are uniquely adapted to the shade.
a. there are climates that are wetter, as in the temperate
rain forests where plant abundance and species diversity are greater, and
climates that are drier, as in the deserts where plant abundance is lower
b. plants within a community respond to the seasons of the year; in
deciduous trees have dropped their leaves and are dormant. Some plants
bloom in the spring,
whereas others bloom in summer
3. soil - the depth and type of soil dictates what kinds of plants
may grow; the soil provides support, inorganic nutrients, water, and suitable
gases for the root systems.
4. All inorganic substances essential for life tend to move in cycles from
the physical environment to organisms, then back to the environment.
plants contribute to the composition of the soil through litter; meaning
the old leaves and stems that have dropped from the trees and accumulated
on the ground surface; these decompose through the action of bacteria and
fungi to produce the organic material in the soil
b. example: the litter
in pine forests is slightly acidic, so the soils in these communities
c. the degree of soil moisture also affects the distribution of plants;
constantly wet soil supports aquatic or marsh
plant communities; succulent
plants often dominate areas where the soil is always dry
d. matter - living organisms are composed of matter or inorganic substances
made of atoms.
A. Biosphere- all of the communities on Earth (i.e., all of Earth's living
Other Sites of Interest:
interactions among Earth's biosphere, atmosphere, water, and land
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Last revised: September 1, 1998 - Browning update 12/2000