Unit 1: Environment- Ecology: Principles and Methods

Ecology is the study of the relationships between organisms and their environment.
A fundamental aspect of ecology involves explaining the distribution and abundance of organisms.
Examples of ecological questions include understanding why elephants use specific watering holes, their distribution patterns, and population dynamics.

Swallowtail caterpillars primarily consume Queen Anne's lace (Apiaceae family).
Apiaceae plants contain toxic secondary metabolites that deter most herbivores.
Some herbivores, like swallowtail caterpillars, have evolved adaptations to detoxify or utilize these compounds.
Swallowtail caterpillars sequester alkaloids from Queen Anne's lace, making them unpalatable to predators.
Their distinct coloration (black, yellow, and white stripes) serves as a warning signal to predators, a concept related to mimicry.
Most caterpillars are specialists, feeding on only one or two plant species. (Spongy moth caterpillars are an exception eating up to 200 species).

Reference: American Naturalist, Vol. 75.
Research Question: Do caterpillars discriminate by smell?
Hypotheses:
- Null Hypothesis: No difference in response to odors from different plants (randomness prevails).
- Alternative Hypothesis: Different responses are elicited by different odors from different plants.

Prediction: Caterpillars will be attracted to filter paper infused with Apiaceae odor.
Methodology:
- Leaves from different plants were ground, blended with water, and filtered.
- Extracts were applied to filter paper inside a petri dish.
- A screen prevented caterpillars from directly touching or tasting the extracts.
- Caterpillars were placed on the screen, allowing them to assess odors.
Result: Caterpillars congregated above the filter paper spots containing plant extract.
Conclusion: Caterpillars discriminate by odor.

Western ragweed thrives in salty soil environments, common in the Great Plains.
High salt concentrations in soil can cause water to flow out of plant roots, leading to dehydration.
Western ragweed has adapted to tolerate high salt concentrations.
Ragweed exhibits clonal growth, using rhizomes to produce clones (genetically identical offspring) some distance from the parent plant.
Clonal growth allows new clones to access the parent plant's resources during establishment.

Hypothesis: Plants can select a microhabitat based on their clonal growth in response to salt concentration.
Null Hypothesis: No difference in clonal growth in response to different salt levels.
Alternative Hypothesis: Clonal growth occurs more in less salty areas.
Prediction: Plants grown in a salt gradient will exhibit greater clonal growth in the less salty areas.

A rectangular box was filled with soil and a salt gradient (1% $NaCl$ on one side, tap water on the other).
A clone was placed in the middle of the box.
Number of shoots in each end (salty vs. non-salty) was measured.
Six replicates per genotype were performed across nine different genotypes.

Replication is crucial for representing variation within a population and ensuring reliable results.
Insufficient replication can lead to inaccurate conclusions due to chance, genetic differences, or experimental errors.
The number of replicates should reflect the variation in the population.

Analysis of nine genotypes showed that, on average, 67% of shoots grew in the non-salty end.
Conclusion: Western ragweed preferentially grows clones in less salty areas.

Goal: To determine if lab results hold true in natural settings.
Plants grown in nonsalty areas should have their clonal growth or shoots nearby, while those in salty areas should be sending their clones farther away from the parent plant.
Clones were planted in salty and non-salty areas, and salt concentration was measured.
After several months, shoots were counted, and the distance from parent plants was measured.

In non-salty areas, 97% of shoots grew less than 20 cm away from the parent plant.
In salty areas, 28% of shoots grew more than 20 cm away from the parent plant, while only 17% grew less than that.
Conclusion: Ragweed can select a favorable habitat through clonal growth, avoiding salty areas.

Why do elephants prefer certain waterholes in a nature preserve?
Potential factors:
- Availability of preferred food near waterholes
- Presence of predators (human or non-human)
- Salt attraction

Herbivores often seek out salt sources due to their diet being high in potassium but low in salt.
Marmots chewing car wires and hoses in Yosemite National Park were attracted to the salt from winter road treatments.

Record waterhole usage of elephants
Assess salt availability differences between waterholes and correlate with waterhole usage to find relationship, but remember that correlation does not mean causation.
Experimentally add salt to a waterhole to see if usage increases
Experimentally remove salt from a waterhole to see if usage decreases.