Rucete ✏ Campbell Biology In a Nutshell
Unit 8 ECOLOGY — Concept 52.2 The Distribution of Terrestrial Biomes Is Controlled by Climate and Disturbance
The distribution of terrestrial biomes depends primarily on climate, especially temperature and precipitation, but is also influenced by disturbances like fire and human activity. Though biomes are often illustrated as distinct zones, they blend gradually into each other and are dynamic systems shaped by both natural and human-induced change.
1. Climate and Biomes
- Climate—long-term patterns of temperature and precipitation—strongly influences plant distribution
- Climographs display the annual mean temperature and precipitation ranges for biomes
- Biomes may have overlapping climate values but differ due to seasonal variation or other factors
- Example: two areas with the same annual values may support temperate broadleaf vs coniferous forests depending on seasonal rainfall
2. Disturbance Shapes Biomes
- Disturbances (storms, fires, human activity) frequently reshape ecosystems
- Example: Hurricane Katrina altered Gulf Coast forests, favoring wind-resistant species
- Many plants are adapted to fire and depend on periodic burning
- Grasslands, chaparral, and coniferous forests rely on disturbance to maintain structure
- Human management uses prescribed fires to preserve biodiversity in fire-adapted biomes
3. Features of Terrestrial Biomes
- Biomes are named for climate and dominant vegetation (e.g., temperate grassland, tropical forest)
- Include distinct microbial, fungal, and animal communities adapted to each biome
- Ecotones are transition zones between biomes and can be wide or narrow
- Vertical layering is common in forests: canopy → understory → shrub layer → herbaceous layer → litter/root layer
- Supports diverse animal niches across these layers
- Species composition varies within biomes depending on region (e.g., different spruce species across taiga)
4. Convergent Evolution Across Biomes
- Similar environments foster similar traits in unrelated species
- Example: cacti (Americas) vs euphorbs (Africa) → similar morphology via convergent evolution
- Despite similarity, these species evolved independently from different ancestors
5. Human Impact
- Humans have significantly altered natural biomes, replacing them with agriculture and urban areas
- Example: central U.S. grasslands were once tallgrass prairie, now mostly farmland
- Conservation efforts aim to protect and restore original biome diversity and structure
In a Nutshell
The location and composition of terrestrial biomes are shaped by climate and constantly modified by disturbances. Though they may appear stable on a map, biomes are dynamic and blend into each other. Climate change and human land use continue to transform these ecosystems, raising urgent questions for conservation and ecological resilience.