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- R vs K strategists decline a long a gradient of decreasing latitude or water temperature applied to only marine invertebrates.
- Hypothesized mechanisms: 2 principal modes of development for mollusks and gastropods.
- 1) the larva may become planktonic and disperse with the water currents away from the natal range.
- 2) Many undergo direct development to adults in the natal home range.
- More pigmented forms in humid areas. Animals are darker close to the equator.
- Animals have less intense pigmentation in less humid areas (higher latitude)
- There is more bacteria in humid areas and darker coloration provides better resistance to microbial organisms.
- Better UV protection.
- Examples: Birds
- forms living in warmer environments (low elevation/low latitude) have longer appendages.
- Shorter appendages promote heat conservation in cold environments by reducing total surface area for heat loss
- Long appendages= heat dissipation (ears/legs)
Tendency for geographic range size to increase with latitude
- Body size of endotherms is positively correlated to latitude
- fewer small endotherms at higher latitudes
- improved cold tolerance
- less evaporative cooling in large endotherms
- Ex: Bears
- Greater predator and prey offenses/defenses toward lower latitudes
- Greater diversity in tropics due to predation pressure causing prey speciation, which in turn contributes to predator speciation.
Why biodiversity is higher in some regions than others.
- Reduced seasonality
- Greater number of niches
- Time for speciation to occur