Ecology Notes – Sept. 11/12
- Ecology is the scientific study of interactions between organisms and their environment. It is the
scientific study of interactions that determine the distribution (geographic location) and abundance
of organisms. Ecology differs from environmental activism and environmental science (which look at
solutions to environmental problems). Ecologists try to explain why organisms are where they are
and what makes them successful.
- General misconceptions in ecology: 1. Balance of nature – natural systems return to their original
preferred state after a disturbance. This is not the case. Things are always changing and random
perturbations often play an important role in nature. 2. Each species has a distinct role to play in
maintaining that balance. This is not the case. There is a lot of redundancy of species and some
species can be lost and the outcome won’t change. Some species are a lot more important than
others. Different species in an area often respond in different ways to changing conditions.
- Ecological maxims (guiding principles): 1. Organisms interact and are interconnected. 2. Everything
goes somewhere. 3. No population can increase in size forever (there are limits). 4. Finite energy and
resources result in tradeoffs (increasing inputs into one function results in a tradeoff in which there
is a loss for other functions). 5. Organisms evolve. 6. Communities and ecosystems change over time.
7. Spatial scale matters (environmental conditions can change from one place to another).
- Ecological hierarchy: organism – population – community – ecosystem – biosphere
- A population is a group of individuals of a single species that are living and interacting in a particular
area. A community is an association of interacting populations of different species that live in the
same area. Ecological studies at the population and community levels often include both the biotic
(living components) and abiotic (physical components) of natural systems. An ecosystem is a
community of organisms plus the physical environment in which they live. Landscapes are areas with
substantial differences from one place to another, typically including multiple ecosystems. They are
large spatial regions. All of the world’s ecosystems comprise the biosphere, which consists of all
living organisms on earth plus the environments in which they live. The biosphere forms the highest
level of biological organization.
- Key terms for studying connections in nature: Adaptation – A characteristic of an organism that
improves its survival or reproduction. Natural selection – Individuals with certain adaptations tend
to survive and reproduce at a higher rate than other individuals. If the adaptation or characteristics
being selected for are heritable, then the frequency of the characteristic may increase in a population
over time. If this occurs, the population will have evolved. Example involving antibiotics – A few
bacteria (blue) in this population have an allele that makes them resistant to an antibiotic. When the
population is exposed to an antibiotic, the resistant bacteria will survive and reproduce at a higher
rate than nonresistant bacteria. The resistant bacteria that survive pass their resistance on to their
offspring. When the population is exposed to the antibiotic again, the proportion of resistant bacteria
in the population increases further. The proportion of resistant bacteria in the person’s body will
increase over time, and the bacterial population will have evolved.
- Ecosystem processes: Producers (autotrophs) capture energy from an external source (ex. the sun)
and use it to produce food. Consumers (heterotrophs) get energy by eating other organisms or their
remains. Net primary productivity (NPP) is the amount of energy captured by producers (by
photosynthesis) minus the amount lost as heat in cellular respiration. How ecosystems work: Each
unit of energy captured by producers is eventually lost from the ecosystem as heat. Energy moves
through ecosystems in a single direction only – it cannot be recycled. But nutrients are continuously
recycled from the physical environment to organisms and back again – this is the nutrient cycle. - Ecological experiments can be done at different scales, such as laboratory experiments, small-scale
field experiments conducted in natural or artificial environments, and large-scale experiments that
alter major components of an ecosystem. In a laboratory experiment, you can control things, but the
results may not be realistic. Small-scale experiments may be conducted outdoors, but in artificial
ponds. This is a semi-controlled experiment that is done in a natural environment and the results are
mostly realistic. In a large-scale experiment, you can’t control things, but the results are realistic.
- Design and analysis of ecological experiments: 1. Assignment of treatments and control. 2.
Replication. 3. Random assignment of treatments. 4. Statistical analyses (statistical vs. biological
significance). Replication (perform each treatment more than once) is good because as the number of
replicates increases, it becomes less likely that the results are due to a variable that was not
measured or controlled in the study. Assigning treatments are random helps limit the effects of
unmeasured variables. Statistical analyses help determine whether results are significant. Ecological
experiments are a lot of work and ecologists try to optimize the least number of replicates while still
being able to obtain desired results.