Ecology topic 16
what are global biodiversity patterns
how species richness, abundance, and types of organisms vary across the Earth. (like why some places have lots of species and other have fewer)
what causes biodiversity patterns
certain ecological and environmental processes
if we can undertsand the processes that create gloabl biodiversity patterns we can
better understand how human activities (climate change) will affect biodiversity in the future
what is latitude gradient in biodiversity
species diversity is highest in the tropics and decreases towards the poles
higher diversity =
lower latitudes (near the equator)
lower diversity =
higher latitudes (towards the poles)
the latitude gradient has been documented for almost every taxon on earth expect for
lichen, penguins, lichenomycota
several hypothese exist on latitude gradient, name them
Rapoport's rule, glacial history, climate, habitat heterogeneity, geometric contraints and niche conservation
what is Rapoports rule
that species’ geographic range sizes increase with latitude. Because high-latitude regions experience more variable climates (cold winters, hot summers), species must survive extreme seasonal changes and therefore evolve broader environmental tolerances and larger ranges. As a secondary consequence, stable tropical climates allow species to specialize, resulting in smaller ranges but much higher biodiversity and species richness.
Rapoports rule on annual climatic stability hypothesized two patterns
latitudinal trend in species geographical range (bigger range in variable climates) and latitudinal gradient in species richness (higher in tropics)
the predicted relationships between annual climate stability and rage size/diversity is
weak or insignificant in many datasets
what are some flaws in Rapaports rule
organisms that avoid weather cannot experience annual climate variability the same way. some also lack latitudinal gradient in diversity
why does Rapoports rules not consistently explain the global latitudinal biodiversity gradient
studies show that annual climate variability is weak/non-significant predictor of species richness and biodiversity gradients appear independently of weather condition stability. many species dont follow it
what are some other problems with Rapoport's rule
empirical inconsistency (evidence shows mechanisms work badly), can be a sampling artefact (less tropical sampling = appears to be small ranges)
what is the glacial history theory
argues that present-day biodiversity patterns, especially in northern regions, are shaped by past glaciations. During the glacial period, much of North America was covered in ice, so these regions had very low diversity and could not support forests or complex ecosystems. After the glaciers retreated, species rapidly recolonized the land, meaning today’s boreal and northern ecosystems are relatively young and not remnants of ancient diversity.
what are the climate-based predictions of species richness
Species richness strongly correlates with temperature, energy and precipitation. climate is the most effective and the best-supported predictor of biodiversity. higher species richness is warmer and wetter environments.
warmer and wetter environments = higher
potential evapotranspiration (PET) = higher species richness
when climate becomes more extreme (very warm/ very wet), relationships sometimes become
nonlinear, therefore predictions are less straightforward
Why do climate–richness relationships become nonlinear in very warm environments?
In very warm regions, temperature alone no longer predicts species richness well because warmth is no longer the limiting factor. Moisture availability becomes the key limit, so adding rainfall/water availability creates a stronger, more accurate prediction.
Temperature works well in cold/temperate regions, but in hot climates you need temperature + moisture together.
why does climate correlate strongly with biodiversity
due to niche conservatism and niche limitations.
what is niche conservatism
Species tend to remain in climates similar to those in which their ancestors evolved. Tropical lineages stay in tropical conditions, resulting in high tropical diversity.
what are niche limitations / species-specific tolerances
each species can only survive in certain habitats and conditions. Climate restricts which species can live where, shaping species richness patterns
why does niche conservatism lead to high tropical diversity
because many lineages evolved in warm tropical climates and tend to retain those ancestral temperature preferences. Since they cannot easily adapt to colder environments, they remain in the tropics, where they persist and diversify over long evolutionary timescales.
how does niche limitations/species-specific tolerances shape richness patterns
because each species can only survive within a certain range of environmental conditions. In harsh or variable climates, only a few species meet these tolerances, leading to low richness, while stable, favorable environments allow more species to persist and coexist.
climate (energy+water availability) predicts
biodiversity patterns very well
what is Habitat heterogeneity
Each species is limited to a specific habitat type. therefore, when habitat diversity increases, species richness should also increase because more habitat types = more niches.
graphs show a positive relationship between
habitat variation and species richness
how can habitat heterogeneity sometimes predict species richness better than climate.
because areas with more diverse habitats provide more niches, allowing more species to coexist. When measured at high resolution, habitat diversity (different land-cover types, structures, and microhabitats) can explain richness patterns even more strongly than temperature or moisture alone. In some regions, the variety of habitats is a stronger driver of biodiversity than climate conditions.