Global Biodiversity Patterns Flashcards
What is the species accumulation curve?
- graphical representation of the number of individual samples needed until the number of species counted reaches a plateau, until only rare ones are left.
- allows you to compare sites
What is an alternative to the species accumulation curve?
- you could control for sampling effort by counting the same number of individuals in each community = relative measure of species richness
What are living fossils?
A living fossil is an extant taxon that closely resembles organisms otherwise known only from the fossil record.
Why is the term ‘living fossil’ misleading / problematic?
Living fossil implies that the animal has remained unchanged since the time its ancestors appear in the fossil records. Phyletic evolution has likely been occurring within the lineages leading to modern living fossils so that their genetics, and perhaps even aspects of their biochemistry and morphology, are different than that of the fossils that have a similar morphology to them. Coelacanths are ‘living fossils’ yet studies have shown they are still evolving today. Likely, the reason the morphology of living fossils remains unchanged is due to stabilizing selection - that morphology has been adaptively advantageous for long periods of time.
- *this term is applied to species that are the only living examples of their lineage, which means their lineages are species poor, not necessarily old.
- *implies frozen in time
Explain the latitudinal gradient of biodiversity patterns.
- observed by Wallace
- negative relationship between latitude and diversity was the most common relationship across taxa aka higher latitude = lower diversity
*species diversity increases as you move from the poles to the tropics
What are the potential four categories of explanations for global biodiversity patterns?
- Null model explanations
- Evolutionary hypotheses
- Historical Explanations
- Ecological Hypotheses
Global Biodiversity Pattern Explanations (latitudinal gradient):
- Explain the following null hypothesis :
1. Null model
- Null model
L> how relationship/pattern should look in nature in absence of a process or mechanism of interest
Global Biodiversity Pattern Explanations (latitudinal gradient):
- Explain the following null hypothesis :
2. Mid domain hypothesis
- pattern may be due to placing species ranges on abounded domain (the earth)…
L>random placement in a fixed surface means more sp will be in the area bc of all the overlap
-L> if place all species on a sphere that is targets in the centre, most range overlaps will occur at the equator
L> model is reasonable explanation for diversity gradients in some bounded regions (mountains), but doesn’t explain global patterns (fit improves if add climate)
L> model assumes species ranges are random, but ranges reflect climate, species history, species interactions
Global Biodiversity Pattern Explanations (latitudinal gradient):
- Explain the evolutionary hypothesis :
- focuses on diversification rates (speciation minus extinctions)
- global patterns of richness controlled by speciation, extinction and dispersal
- assume that dispersal rates similar globally -> species richness reflects balance between extinction and speciation
- species diversification rate = speciation rate - extinction rate (net change in species over time
- *ignores dispersal…meaning diversification is just the rise of new sp and extinction of old without gene flow…can’t be right
Global Biodiversity Pattern Explanations (latitudinal gradient):
- Explain the area component to the evolutionary hypothesis.
- rate of diversification is higher in the tropics
- larger area in the tropics vs northern and southern hemisphere
- Species area relationship
L> area curves plot species richness against area..linear regression estimates there relationship.
L> as area increases so does the number of species
**more variation in habitat therefore can support more niches
Why is the rate of diversification higher in the tropics if you go by and evolutionary hypothesis explanation?
- species area effect (larger area in tropics)
- more stable climate
- speciation is higher (more are a= more likely for isolation of populations)
L> isolation by distance - extinction is lower due to climatic stability and larger surface area (supports larger populations)
Explain biodiversity patterns with under the historical hypotheses?
- diversification rates are similar but evolutionary time is greater in the tropics
- tropics are more climatically stable over time than temperate regions (temperate and polar regions = higher level of disturbance)
- so longer evolution history for lineages involved
- even if extinction and speciation rates are the same globally, the tropics have had more TIME for uninterrupted evolution
**most of the worlds biodiversity is found in warm evergreen broadleaf forests of tropics (mega thermal forests)
The tropics are said to be both a cradle and a museum. Explain what this means.
- tropics are a cradle because most species originated there and dispersed to other areas
- tropics are a museum because extinction rates are lower there (species persist for longer periods)
- a lot of terrestrial sp have their ancestry in the traps..lots one endemic sp in tropics (either bc lineages never separated out or anything that tried wasn’t successful ) **
The tropics have likely acted as a refuge for warm adapted species in times of global cooling and a source of colonists in times of global warming in the past. How is climate change predicted to impact the tropics? What effects might this have on global biodiversity ?
The tropics are both the place where most species originate and also the only place where many ancestral lineages exist. In the past mass extinctions were followed by adaptive radiation from the remaining lineages. Most of them survived in the tropics. If extinctions occur in the tropics as well, then this could impact the planets ability to replace species after mass extinction vents. It could also result in the disappearance of many ancestral lineages that have been around a long time, having survived other mass extinction events in the tropical region
Global Biodiversity Pattern Explanations (latitudinal gradient):
- Explain the ecological hypotheses.
- focus on the carrying capacity of different areas / primary productivity levels
- climate variables explain a significant amount of global richness variations across broad range of taxa
- measures of energy (isolation, temperature), water (precipitation), or water energy balances are strongest predictors (esp water variables)
- species energy hypothesis
L> the number of individuals na area can support increases with primary productivity (which is influenced by climate)
*more plants = more herbivores = more carnivores = more parasites
