Ecology Final Exam Notes

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9 Dec 2013
1. The scientific study of interactions between organisms and their environment
2. The scientific study of interactions that determine the distribution (geographic location) and abundance of
Other meanings in public usage
Differs from environmental activism and environmental science (solutions to environmental problems)
General Misconceptions
Balance of nature return to original preferred state after disturbance
Each species has a distinct role to play in maintaining that balance
Ecological Maxims (Guiding Principles)
1. Organisms interact and are interconnected
2. Everything goes somewhere
3. No population can increase in size forever
4. Finite energy and resources result in tradeoffs
Tradeoffs can be thought of as an investment of energy by species
5. Organisms evolve
6. Communities and ecosystems change over time
Change can happen either very rapidly or very slowly, depending on the species; biased/limited by
our own perception because of our own lifespan so we overlook changes
7. Spatial scale matters
Ecological Hierarchy
Population: group of individuals of a species that are living and interacting in a particular area
Community: association of populations of different species in the same area
Ecological studies often include both the biotic (living components), and abiotic (physical components) of
natural systems
Ecosystem: community of organisms plus the physical environment
o An ecosystem is not simply a collection of communities, but nutrients, water, and abiotic
components are considered
o Landscapes are collections of ecosystems
Landscapes: areas with substantial differences, typically including multiple ecosystems
All the world’s ecosystems comprise the biosphereall living organisms on Earth plus the environments in
which they live
Key Terms for Studying Connections in Nature
Adaptation: a characteristic that improves
survival or reproduction
Natural selection: individuals with certain
adaptations tend to survive and reproduce at a
higher rate than other individuals
If the adaptation is heritable, the frequency of
the characteristic may increase in a population
over time
Ecological Experiments can be done at Different Scales
Lab work microbial activity in response to a
certain environmental stressor can be tested in
the lab; a disadvantage, however, is that
realistic information is lost
Studies in natural environment less control in
comparison to lab work
Artificial unit is placed in a natural environment
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Ecosystem Processes
Producers capture energy from an external source (e.g. the sun) and use it to produce food
Net primary productivity (NPP): Energy captured by producers, minus the amount lost as heat in cellular
respiration currency with which we describe ecosystems
Consumers get energy by eating other organisms or their remains
Ecological Experiments: Design and Analysis
1. Assignments of treatments and control
2. Replication
3. Random assignment of treatments
4. Statistical analyses (statistical vs. biological significance)
Scientific Method
Scientists use a series of steps called the scientific method:
1. Make observations and ask questions
2. Use previous knowledge or intuition to develop hypotheses
3. Evaluate hypotheses by experimentation, observational studies, or quantitative models
4. Use the results to modify the hypotheses, pose new questions, or draw conclusions about the natural
The process is iterative and self-correcting
Sometimes experiments cannot be done due to scope or scales, so instead, modeling approaches are used
(e.g. computerized stimulations)
Case Study: Deformity and Decline in Amphibian Populations
High incidence of deformities in amphibians
Declining populations of amphibians
Amphibians are “biological indicators” of
environmental problems because of their
vulnerable physiological characteristics
o Skin is permeable; pollutant
molecules can pass through easily
o Eggs have no protective shell
o They spend part of life on land and
part in waterexposed to pollutants
and UV in both environments.
Observation of Pacific tree frogs suggested
that a parasite could cause deformities
Small glass beads implanted in tadpoles to mimic the effect of cysts of Ribeiroia ondatrae, a trematode
flatworm, also produced deformities
Further studies: deformities of Pacific tree frogs occurred only in ponds, which also had an aquatic snail,
Planorbella tenuis, the intermediate host of the parasite
The Life Cycle of Ribeiroia
More complex life cycle for parasite in comparison to other species
Contingent on other species that need to be present in the environment
for them to cleave their lifecycle properly
A controlled experiment:
o Tree frog eggs were exposed to Ribeiroia parasites in the lab
o Four treatments: 0 (the control group), 16, 32, or 48 Ribeiroia
A field experiment:
o Six ponds, three with pesticide contamination
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o Six cages in each pond, three with mesh size that allowed parasite to enter
Hypothesis: pesticides decrease the ability
of frogs to resist infection by parasites
Another lab experiment: Tadpoles reared in
presence of pesticides had fewer white
blood cells (indicating a suppressed immune
system) and a higher rate of Ribeiroia cyst
Studies have suggested that a range of
factors may be responsible for amphibian
The relative importance of factors such as
habitat loss, parasites, pollution, UV
exposure, and others are still being
Synthetic pesticide use began in 1930s; use
has increased dramatically.
Amphibian exposure to pesticides has also
Any action (increased use of pesticides) can
have unanticipated side effects (more
frequent deformities in amphibians)
Interaction non-additive effect
difference between ponds with and without
Not a fully controlled experiment, so link between pesticide and deformation is not strong
Fertilizer use may also be a factor:
o Fertilizer in runoff to ponds increases algal growth
o Snails that harbor Ribeiroia parasites eat algae
o Greater numbers of snails result in greater numbers of
Ribeiroia parasites
Skerrat et al. (2007) argued that some declines may be due to
pathogens such as a chytrid fungus that causes a lethal skin disease,
and has spread rapidly in recent years
But climate change and altered conditions may be favoring growth
and transmission of disease organisms
Hatch and Blaustein (2003) studied the effects of UV light and nitrate on Pacific tree frog tadpoles
o At high elevation sites, neither factor alone had any affect. But together, the two factors reduced
tadpole survival
o At low elevation sites, this effect was not seen
Stuart et al. (2004) analyzed studies on 435 species:
o Habitat loss was the primary cause for 183 species; overexploitation for 50 species
o The cause for the remaining 207 species was poorly understood
Case Study: Salmon Decline
Potential causes of salmon declines in the North Pacific Ocean:
o Dam construction
o Sediment from logging operations
o Water pollution
o Overharvesting
But the conditions of oceans, where salmon spend most time as adults, have also been implicated.
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