Rucete ✏ Campbell Biology In a Nutshell
Unit 8 ECOLOGY — Concept 54.1 Interactions Between Species Can Help, Harm, or Have No Effect on the Individuals Involved
Species living together in communities interact in various ways that affect their survival and reproduction. These interspecific interactions include competition, exploitation (like predation or herbivory), and positive interactions (like mutualism or commensalism), with consequences ranging from beneficial to harmful or neutral.
1. Types of Interspecific Interactions
- Competition (-/-): both species are harmed as they compete for resources
- Exploitation (+/-): one benefits, the other is harmed
- Includes predation, herbivory, parasitism
- Positive interactions:
- Mutualism (+/+): both benefit
- Commensalism (+/0): one benefits, other unaffected
2. Competition and the Competitive Exclusion Principle
- Species competing for the same limited resources cannot coexist permanently
- Example: Paramecium aurelia outcompetes P. caudatum
- Known as competitive exclusion
3. Ecological Niches and Resource Partitioning
- Niche: all resources a species uses
- Resource partitioning: species evolve to reduce overlap (e.g., Anolis lizards)
- Fundamental niche: potential space
- Realized niche: actual used space due to competition
- Example: Connell’s barnacles showed niche exclusion in tidal zones
4. Character Displacement
- Sympatric species evolve to reduce overlap
- Example: Galápagos finches show greater beak divergence when living together
5. Predation
- One species kills and eats another
- Adaptations:
- Predators: speed, claws, camouflage
- Prey: behavior, toxins, warning colors, mimicry
- Batesian mimicry: harmless mimics harmful
- Müllerian mimicry: two harmful species mimic each other
- Mimic octopus: impersonates various marine animals
6. Herbivory
- Herbivore eats plant or algae
- Plants defend via spines, toxins (e.g., nicotine, tannins)
- Herbivores have adaptations to locate and digest plant matter
7. Parasitism
- Parasite harms host while feeding
- Endoparasites: internal (e.g., tapeworms)
- Ectoparasites: external (e.g., ticks)
- Some require multiple hosts and modify host behavior
8. Mutualism (+/+)
- Both benefit, despite potential costs
- Examples:
- Ants & acacia: protection in exchange for food/shelter
- Mycorrhizae: fungi & plants exchange nutrients
- Pollinators, gut microbes, coral algae
9. Commensalism (+/0)
- One benefits, other unaffected
- Examples:
- Cattle egrets feeding near buffalo
- Wildflowers shaded by trees
- Can evolve into mutualism
In a Nutshell
Species interactions are central to community structure. They include competition, exploitation, and cooperation, each influencing survival, reproduction, and species distributions. These relationships—shaped by evolution and ecology—can shift over time, making communities dynamic systems of interdependence and adaptation.