Lecture 6 Species Interactions and Changes

Definition: A species that has a disproportionately large effect on its environment relative to its abundance.
Example: Southern sea otter
- Controls sea urchin population, which affects kelp forests.
- Historical context:
  - Once numbered around 16,000 off California, nearly hunted to extinction.
  - Declared endangered in 1977; population rose to about 3,000 by 2020.
- Threats: Climate change and pollution, such as agricultural runoff and herbicides.
- Implications: Loss of sea otters could drastically reduce biodiversity in coastal ecosystems.

Types of Interactions:
- Competition:
  - Interspecific (between species) and Intraspecific (within the same species).
- Predation: Predator feeds on prey.
- Parasitism: One organism benefits at the expense of the host.
- Mutualism: Both species benefit from the interaction.
- Commensalism: One species benefits while the other is unaffected.
Impact on Ecosystem: These interactions affect resource use and population dynamics.

Competition: Leads to resource sharing (food, shelter, mates).
- Resource Partitioning: Competing species evolve specialized traits for resource use.

Predator Strategies:
- Various methods for capturing prey (e.g., speed, camouflage, social hunting).
Prey Defenses:
- Evasion tactics (speed, sensory adaptations), physical defenses (shells, spines), chemical defenses (toxicity), and behavioral adaptations (group living, mimicry).
Coevolution: Long-term interactions can lead to evolutionary changes in both predators and prey. E.g., moths evolving against bats.

Parasitism: Parasites depend on hosts for survival; examples include tapeworms and mistletoe.
Mutualism: Benefits both organisms, e.g., birds cleaning pests off large mammals and bacteria aiding in digestion.
Commensalism: One organism benefits without affecting the other; e.g., epiphytes using trees for support.

Definition: The gradual process of species composition changes in response to environmental shifts.
Types:
- Primary Succession: Occurs in lifeless areas (e.g., after glacier retreat).
- Secondary Succession: Occurs in areas where disturbances have happened but soil remains (e.g., post-fire regrowth).
Benefits of Succession: Enhances biodiversity, complex food webs, and nutrient cycling.

Ecological Inertia: Ecosystem's ability to resist disturbance.
Ecological Resilience: Ecosystem's ability to recover from disturbances.
Examples of Resilience:
- Tropical forests: High diversity but low resilience with climate change impacts.
- Grasslands: Low diversity but high resilience due to underground nutrient storage.

Population Definition: A group of interbreeding individuals of the same species in a defined area.
Factors Affecting Population Size: Births, deaths, immigration, and emigration.
Age Structure: Comprises pre-productive, reproductive, and post-reproductive stages affecting growth rates.

Range of Tolerance: The range of environmental conditions a population can endure.
Limiting factors in different systems:
- Terrestrial: Precipitation, soil nutrients.
- Aquatic: Temperature, depth, clarity, acidity.

Density-Dependent Factors: Impact population size as density increases (e.g., disease).
Density-Independent Factors: Affect population size regardless of density (e.g., drought).
Population Growth Curves:
- J-Curve: Exponential growth until resources become limited.
- S-Curve: Logistic growth reflecting carrying capacity limits.

Population Crash: Occurs when a population exceeds its carrying capacity.
Reproductive Patterns:
- r-selected species: High reproduction rate, short lifespan, less parental care.
- K-selected species: Lower reproduction rate, longer lifespan, more investment in offspring.
- Survivorship Curves: Illustrate how mortality varies within a population over time.

Historical Crashes: Examples include the Irish Potato Famine and the 14th-century plague.
Carrying Capacity: Influenced by technological and cultural developments that expand human population limits.