Predation, Parasitism, and Community Ecology

Community and Species Interactions

• Community: A group of interacting species occurring together in time and space.
  • At least two different species interacting.
  • Types of species interactions:
  • Positive: mutual benefit
  • Negative: harm to one species
  • Neutral: no effect on either species

Predation Definitions and Types

• Predation: One species feeds on another, resulting in direct benefit to one species and direct harm to the other.
  • Types of predation:
  • Carnivory: Animals eating other animals (prey is killed).
  • Herbivory: Animals eating autotrophs (typically harms but does not kill the autotroph).
  • Parasitism: Symbiosis where the parasite benefits at the host's expense, harming but not killing the host immediately.
  • Parasitoid: Larvae feed on the host and almost always kill it, common in insects.

Dietary Preferences and Foraging Strategies

• Optimal Foraging Theory: Food choices depend on the encounter rate of prey and handling time.
  • Generalists vs. Specialists:
  • Carnivores tend to be generalists; they consume prey based on availability and encounter rates.
  • Herbivores are often specialists; they rely on specific plant parts for nutrients (leaves, stems, fruits).

Nutritional Content by Plant Parts

• Leaf Nutrient Content:
  • Highest in seeds.
  • Leaves from angiosperms and gymnosperms have high nutrients.
  • Phloem sap is intermediate, while xylem sap contains low nutrients.

Types of Herbivores

• Large mammals (grazers/browsers), other vertebrates, and insect types (leaf miners, nectar-eaters) have specific diets.
  • Many herbivores show narrow diets, focusing on few plant species.

Carnivore Adaptations

• Capture tactics include:
  • Foraging and hunting (wolves, lions).
  • Ambush hunting (eels, snakes).
  • Traps (spiders, carnivorous plants).
• Physical features to capture prey:
  • Sharp teeth, flexible jaws, claws, venom.
• Defensive adaptations of prey:
  • Size, speed, toxic compounds, behavioral strategies (e.g., hiding).

Herbivore Defense Mechanisms

• Plants evolve defenses too, such as:
  • Structural defenses: Tough leaves, spines, thorns (cacti, roses).
  • Chemical defenses: Secondary metabolites that deter herbivory (e.g., toxins).
  • Compensation: Re-growth after herbivory.

Predation and Its Ecological Impact

• Predator-prey population dynamics:
  • Cycle based on predator presence affecting prey populations.
  • Example: Hares and lynxes having oscillating population sizes.
  • Lotka-Volterra Model: Mathematical representation of predator-prey interactions where predator abundance depends on prey density.

Parasitism and Disease Dynamics

• Parasites: Organisms that derive nutrients from a host, typically harming it (e.g., protozoa, nematodes).
  • Ectoparasites (external) vs. Endoparasites (internal).
• Pathogens: Parasites causing diseases in hosts.
• Host defenses include immune responses and behavioral adaptations.

Competition in Ecological Systems

• Competition: Non-trophic interactions negatively impacting resource availability for participants.
  • Interspecific competition: Between different species.
  • Intraspecific competition: Between individuals of the same species.
• Liebig's Law of the Minimum: Growth limited by the most scarce resource.

Competition Outcomes

• Competitive exclusion: One species outcompetes another for resources.
• Coexistence: Different species can survive through resource partitioning or character displacement.
• Types of competition:
  • Interference competition: Direct competitive interactions.
  • Exploitation competition: Indirect competition through shared resource usage.

Mutualisms and Ecological Relationships

• Mutualism: Positive interactions where both species benefit (+/+).
  • Examples include pollination and mycorrhizal relationships.
• Facultative vs. Obligate: Type of mutualism can vary; some species can survive without the relationship (facultative) while others cannot (obligate).

Community Dynamics and Succession

• Primary succession: Development in lifeless areas (e.g., bare rock after volcanic activity).
• Secondary succession: Recovery in previously inhabited areas (e.g., after a fire).
• Climax community: Final stable community of a particular area.

Community Interactions and Feedback Mechanisms

• Species interactions can change community structure (e.g., keystone species altering food webs).
• Community resilience and resistance to disturbances.

Conservation and Biodiversity Management

• Conservation biology: Efforts to study, protect, and manage biodiversity.
• Biodiversity threats: Habitat loss, climate change, invasive species.
• Strategies: Ecosystem restoration, protection policies, and managing species risk.
• Relevant assessments include the IUCN Red List for endangered species evaluations.

Final Notes on Community and Landscape Ecology

• Landscape ecology examines spatial patterns and processes affecting communities.
• Understanding these dynamics is crucial for effective conservation strategies and ecosystem management.