Rucete ✏ Campbell Biology In a Nutshell
Unit 8 ECOLOGY — Concept 52.4 Interactions Between Organisms and the Environment Limit the Distribution of Species
The distribution of species is shaped by both ecological and evolutionary factors. Some species are confined to particular regions due to historical events like continental drift, while others are limited by physical conditions or biological interactions in the environment.
1. Historical and Evolutionary Constraints
- Kangaroos are found only in Australia due to evolutionary origin and isolation
- Species ranges reflect both history and environment
- Dispersal is essential in determining whether a species can reach a new habitat
2. Dispersal and Range Expansion
- Dispersal = movement away from origin or high-density areas
- Example: cattle egret spread from Africa to the Americas within the past century
- Some range expansions lead to adaptive radiation (e.g., Hawaiian silverswords)
- Species transplants test whether a species is absent due to dispersal limitation
- Successful transplant = species could live there but hasn't dispersed yet
3. Biotic Factors Limiting Distribution
- Includes predators, herbivores, parasites, pathogens, and competitors
- Example: sea urchins (C. rodgersii) limit seaweed distribution in Australia
- Biotic interactions may prevent survival or reproduction in certain areas
4. Abiotic Factors
- Temperature: affects enzyme activity, survival; extremes can be lethal
- Water and oxygen: critical for cellular respiration; aquatic systems may have oxygen-poor zones
- Salinity: influences osmoregulation; most organisms are adapted to either freshwater or saltwater
- Sunlight: needed for photosynthesis; light penetration limits aquatic life
- Rocks and soil: affect plant growth through pH, mineral content, and texture
- Example: alpine tree lines are limited by UV exposure, wind, and freezing temps
5. Complex Interactions
- Abiotic and biotic factors often interact to determine species distribution
- Example: saguaro cacti are limited by freezing temps, water availability, herbivores, pollinators, and disease
- Multiple factors must be tested to explain why a species is present or absent
6. Rapid Feedback Between Ecology and Evolution
- Ecological changes (e.g., predator expansion) can cause evolutionary changes in prey
- Evolutionary changes (e.g., guppy diet shifts) can alter ecosystem structure
- Example: guppies evolved under low predation consumed more algae, reducing algal biomass
- Highlights reciprocal influence between environment and species traits, even in short timescales
In a Nutshell
Species distributions result from a combination of ecological and evolutionary factors. Dispersal ability, interactions with other species, and the physical environment all play roles in determining where organisms live. These influences are dynamic—ecological shifts can drive evolution, and evolved traits can reshape ecosystems.