Ecology Lecture Sept. 4th

The scientific study of interactions between organisms and their environment.
Also studies interactions that determine the distribution (geographic location) and abundance of organisms.
Distinct from public activism and from environmental science focused on solutions.

Common misconception: a stable ‘balance of nature’ with each species playing an equal role.
Real systems: disturbances can prevent return to original state; random effects are important; species play different functional roles.

Ecological hierarchy:
- Organism
- Population
- Community
- Ecosystem
- Biosphere
Biotic vs. Abiotic components:
- Biotic: living components
- Abiotic: physical components
Definitions:
- Population: group of individuals of a species in a given area
- Community: association of populations of different species in the same area
- Ecosystem: community plus the physical environment
- Biosphere: all living organisms on Earth plus their environments

Energy flow: E
ightarrow ext{ecosystem}; energy moves in a single direction—cannot be recycled.
Nutrient cycling: N ext{ cycles through the environment and organisms}; nutrients are recycled between abiotic and biotic components.

Ecological studies typically include both biotic (living) and abiotic (physical) components.

Major topic areas include: environmental variation (temperature, water, energy), evolution and ecology, life history, behavioral ecology, population dynamics, predation/herbivory, parasitism, competition, mutualism, community change, biogeography, diversity, production, energy flow, and nutrient cycling.
Textbook alignment: Lectures map to chapters; some chapters may be skipped; readings are mandatory; exams focus on lecture material.

Steps:
1) Make observations and ask questions.
2) Develop hypotheses from prior knowledge.
3) Evaluate hypotheses via experiments, observational studies, or models.
4) Use results to refine hypotheses or draw conclusions.
Nature of the process: iterative and self-correcting.

Key design aspects:
- Treatments and controls
- Replication
- Random assignment of treatments
- Statistical analyses (statistical vs. biological significance)

Amphibians as biological indicators due to permeable skin, fragile eggs, and dual aquatic-terrestrial life stages.
Case focus: deformities linked to Ribeiroia ondatrae (a trematode parasite).
Observational finding: deformities occurred in ponds that also contained an aquatic snail (parasite intermediate host).
Lab demonstration: beads inserted in tadpoles could mimic parasite impact, supporting a potential mechanism.
Field link: higher deformities in ponds with both parasite exposure and specific ecological contexts.
Controlled lab experiment: eggs exposed to parasites at varying levels (0, 16, 32, 48 parasites).
Field results (pesticide interaction): field ponds with pesticide contamination showed higher deformity rates vs. pesticide-free controls.
Deformity rates (illustrative field data): control ponds ~4% deformities; pesticide-contaminated ponds ~29% deformities.
Mechanisms for pesticide effects:
- Pesticide exposure can suppress immune responses (e.g., fewer white blood cells) and increase parasite cyst formation.
- Predator presence can heighten pesticide lethality in tadpoles (lab result: up to 46\times lethality when predators are sensed).
Additional factors:
- Fertilizer runoff may boost algal growth, boosting snail populations and, consequently, Ribeiroia transmission.
- Introduced fish predators can influence amphibian populations via changes in predator–prey dynamics.

Across 435 studied species, habitat loss is the primary driver for 183/435 \approx 0.42 of cases; overexploitation affects 50/435 \approx 0.11; remaining cases are poorly understood (≈ 207/435 \approx 0.48).
The relative importance of habitat loss, parasites/disease, pollution, UV exposure, and other factors is still being investigated.

Ecologists use the scientific method to understand interactions and processes.
Results can be context-dependent; multiple factors often interact to shape outcomes.
Field and lab experiments complement each other in uncovering mechanisms.
Understanding energy flow, nutrient cycling, and hierarchical organization helps explain ecosystem function and responses to disturbance.