Lecture 14: Biotic Homogenization Flashcards
Why are marine species apparently less at risk of extinction by invasion?
- long range dispersal of larvae rescues declining populations ASSUMING most marine sp have broad geographic distributions and large metapopulatiosn and that long duration of planktonic larvae in the water column i common (concept of the sea as a giant bathtub in which organisms slosh around form one continental shelf to another)
What is a meta population
- population of populations
- groups connected by dispersal of individuals from one habitat to another
Issues with saying marine species are less at risk of extinction via invasion?
- few studies on impacts of marine invasions
- extinction of small inconspicuous species may be overlooked
- most small species do not have long lived planktonic larvae (coral reef inverts ex)
- many small species have small ranges and therefore greater extinction risk
How did two endemic rats disappear from christmas island?
- island was never developed by humans
- mining opérations were done locally but rats deal with a lot of disturbance
-ships came
L> what was on them? Black rats and brown rats - european black rat is the most invasive sp in the world (rat)
- no hybridization occurred
- infectious blood parasite was found, native rats were naive to it and were wiped out
Contrast historical and current causes of extinctions for mammals
- historical: harventing and invasions were equal
- current: habitat destruction 50%, harvesting 36% and invasions 12%
Contrast historical and current causes of extinctions for molluscs
- historical: habitat destruction >invasions> harvesting
- current: Invasions> habitat > harvesting
**habitat destruction can pave the way for invasions
List the causes of species endangerment in the US
- Invasions
- Urbanization
- Agriculture
- Outdoor recreation and tourism development
- Ranching activities
- River alteration
Explain what happens with the proportion of native sp vs exotic fish sp over time in tow river sites?
- invasion progresses, knocking out native species , the invaders themselves are common unlike the endemic species wiped out SO you start to see a homogenization
Are species declining in range more than they are increasing in range?
- yes
- a small number of widespread species are replacing a alter number of endemic species
What are the two levels of species diversity
- alpha = number of species at a single site
- lambda = number of species within a region
- beta= difference in species richness across sites
What does a high beta diversity mean?
- means that the cumulative number of species encountered will increase rapidly as additional sites are sampled
**Whittaker’s Equation = Y/S -1
S= average number of species at each site
What is the species area effect?
- species richness increases with area
- not directly proportional
S= CA^z
If you had an island with 100 app what would happen if the area was divided in half with a dispersal barrier?
- you would have representatives of the app on both sides if they were equally spread
- if the island was at equilibrium with the 100 spp that means it can not hold more than that
- THEREFORE predict a drop in species.
If you removed a dispersal barrier on an island with 50 species on each side. What would happen?
- briefly the island will have 100spp all together BUT there will be some loss via competitive processes
Give a paleobiological example for species area effects of invasion.
- The Great American Faunal Exchange
L> 3 mya
L> N and S America became connected by the Panamanian land bridge
-Mammals moved north ( opossum, porcupine, armadillos etc) and south (bears, horses, rabbits etc) - at first this interchange increased species richness in both regions but later a series of extinctions occurred
