lecture 7 Flashcards
How many plant species are there? How many are discovered annually?
~ 300,000 known plant species worldwide
> 60 new plant species discovered every year
What are global biodiversity hotspots? Why are they important?
contain some unique rare species: High levels of endemics
➢ High level of threat
➢ Contain ~50% of the world plant species
➢ Occupy ~ 2% of earth’s terrestrial area.
How may increasing nitrogen deposition affect global biodiversity hotspots?
increased growth of often weedy species, cation depletion in the soil, nutrient imbalances in plant tissue, and soil acidification
How does plant richness vary with latitude? Longitude? Elevation? Why?
❑ Latitudinal gradient
❖ Species ranges are bounded by North & South poles
❖ More species along the Equator where their ranges can freely overlap
❑ Longitudinal gradient
❖ Species ranges are bounded by coasts
❖ More species mid-continent where their ranges can freely overlap
❑ Elevational gradient at Santa Catalina Mts.
❖ Species ranges bounded by mountaintops and desert at low elevations
❖ More species in mid-elevations
What does bounded hypothesis for species richness patterns state?
Species ranges are bounded by geographic constraints
How may available energy affect richness patterns? Why?
➢ Greater available energy supports greater growth & reproduction
➢ Greater growth & reproduction lead to more individuals
➢ More individuals lead to greater species richness (α diversity) due to:
❑ Random placement (statistical sampling effect)
❖ greater number of individuals increases the likelihood of including rare species
❑ Decreased local extinction
❖ likelihood of local extinction decreases when local population size increases
❑ Speciation
❖ speciation rate increases with population size
Contrast energy availability hypothesis with history hypothesis.
History
More time since disturbance allows more complete
colonization and the evolution of new species
Contrast energy availability hypothesis with area hypothesis.
Area Hypothesis
❑ Tropics are more species rich than temperate zone due to greater land area in the Tropics
(1) Greater area facilitates speciation due to isolation (also more individuals)
(2) Spatial heterogeneity increases with area (cf. Habitat heterogeneity hypothesis)
Contrast energy availability hypothesis with stress hypothesis.
Climate
(= Stress Hypothesis) Benign (favorable) conditions permit more species;
conditions unfavorable for plant physiology & growth
(e.g., frost) limit the number of species
What are the theories that may explain humped species richness patterns peaking at intermediate
productivity patterns? How?
➢ Space preemption
❑ Individual increase in size at large levels of productivity, thus population sizes decrease
➢ Disturbance
❑ Intermediate disturbance increases coexistence of species differently capable to
tolerate disturbance (& disturbance is positively correlated to productivity)
➢ Herbivory
❑ Intermediate herbivory increases coexistence of species adapted to different levels
(higher and lower) of herbivory (& herbivory is positively correlated to productivity)
➢ Habitat availability
❑ Intermediate habitats are most common, so most species evolved in them
➢ Resource competition & habitat heterogeneity
❑ Different species from extremes of productivity gradient coexist at intermediate levels
composed of different habitat patches (some productive, some less so)
➢ Transport limitation
❑ Habitat heterogeneity is greatest at intermediate productivity levels
What are overall plant and tree species richness patterns in North America? Where are these groups most species rich? Why?
warmer areas have more species righness- more productive conditions
How does species range size relate to species richness and environmental conditions? Why?
Negative relationship- least species rich areas have the largest species ranges and vice versa
What happens to species richness at transition zones? Why?
Transition zones are overlaps between communities,
regions, or biomes where species from two adjacent
areas coexist, thus increasing richness
What is the latitudinal gradient in beta diversity? What does it look like? Why?
Generally decreases with increasing latitude, because colder conditions will have less richness
What is the relationship of regional species pool and local species richness?
Beta diversity
