Chapter 18: Biogeography Flashcards
What are important regulators of species distributions at local scales?
physical factors and species interactions
What are global and regional scale processes important for?
determining the distributions and diversity of species on Earth
Biogeography
study of variation in species composition and diversity across geographic locations
What did the biogeographical forest tour reveal about species richness and composition?
It showed that they varied
-With latitude: low latitudes have more and different species than higher latitudes
-From continent to continent, even where longitude and latitude are similar
-Within the same biome type, depending on its location on Earth
Global Scale
the entire world
How does the global scale affect species?
species have been isolated from one another, on different continents or in different oceans, by long distances and over long periods
-Rates of speciation, extinction. and dispersal help determine differences in species diversity and composition
Regional Scale
areas with uniform climate; species are tied to that region by dispersal limitations
Regional Species Pool
all species contained within a region (gamma diversity)
Landscape Scale
determined by topographic and environmental features
Why does species composition and diversity vary within a region?
depending on how the landscape shapes rates of migration and extinction
Local Scale
equivalent to a community
Alpha Diversity
species physiology and interactions with other species are important factors in the resulting species diversity
Beta Diversity
change in species. or turnover, from one community type to another; connects local and regional scales
How is area determined?
-actual area of spatial scales depends on the species and communities of interest
-area used to define species diversity measurements can be critical to interpreting the processes controlling biogeographic patterns
What does the regional species pool provide for the local scale?
provides raw material for local assemblages and sets the theoretical upper limit on species diversity for communities
-the relative influence of regional and local processes can be determined by plotting local versus regional species richness
If regional and local species diversity are equal…
-slope= 1
-all species in a region will be found in all communities
-This is not very likely as regions will always have features that exclude some species from some communities
If local richness is proportional to regional richness….
community richness is mostly determined by the regional species pool
If local richness levels are off…
local processes can be assumed to limit local species diversity
Witman et. al (2004)
looked at invertebrate communities on subtidal rock walls at 49 sites in 12 regions around the world
-local species richness was always lower than regional species richness
-regional species richness explained 75% of the variation in local species richness
Alfred Russel Wallace
father of biogeography
-co discovered of the principles of natural selection
-main contribution was the study of species distributions across large spatial scales
What did Wallace publish in The Geographical Distribution of Animals in 1876?
-He overlaid species distributions on top of geographic regions and revealed two global patterns
-1. The land masses can be divided into six biogeographic regions, which correspond roughly to Earth’s major tectonic plates
Continental Drift
tectonic plates are sections of Earth’s crust that move or drift through the action of currents generated deep within the molten rock mantle
What is the result of continental drift?
unique flora and fauna in some regions
Where can the legacy of continental drift be found?
in the fossil record and existing taxonomic groups
Vicariance
evolutionary separation of species by barriers such as those formed by continental drift
Holt et al. (2013)
used phylogenetic information from DNA analysis and recent observations of species distributions
Barriers to exchange of biota
continents, currents, thermal gradients, water depth changes
What has hindered the identification of marine regions?
water depth and the basic lack of knowledge of the deep oceans
Willig et al. (2003)
complied results of 162 studies on many taxonomic groups
-negative relationships between latitude and diversity were by far the most common
Has the latitudinal gradient in species diversity observed by Wallace been documented repeatedly?
Yes
Gaston et al. (1995)
measured number of families along multiple north-south transects
-number of families increased at low latitudes but also depended on longitude
-biodiversity hot spots are areas of high species richness that are under threat from human activity
Where do some groups have higher diversity at?
temperate and polar latitudes
What are global patterns of species richness are ultimately controlled by?
rates of speciation, extinction, and dispersal
What should species richness reflect a balance between?
extinction and speciation (assuming similar dispersal rates)
Rate of species diversification
-net increase or decrease of species over time
-speciation rate minus extinction
Mittelbach et al. (2007)
summarized the species diversification hypotheses in three categories
1. species diversification rate is higher in the tropics
2. diversification rates are similar, but evolutionary time is greater in the tropics
3. higher productivity results in more abundant resources in the tropics
Species Diversification Rate
-the tropics have the most land on Earth, and temperatures are very stable
-large, thermally stable areas should decrease extinction rates-population sizes and geographic ranges would be larger
-Speciation by geographic isolation would be more likely
Species diversification time
-The tropics are thought to have been more climatically stable over time, and species have had more time to evolve
-Temperate and polar regions have undergone severe climatic changes such as glaciation, disrupting species diversification
What are the tropics considered?
the cradle of diversity or a museum (species that diversify there tend to stay there)
How did most species originate?
They originated in the tropics and move to other regions during warm climatic periods
Productivity
-terrestrial productivity is highest in the tropics
-higher productivity leads to lower extinction rates, more coexistence, and overall higher species richness
-But some very productive habitats, such as estuaries, have low species diversity
Mannion et al. (2014)
compared the fossil record with fluctuations in past global temperatures
Read slides 59-62
Species-Area relationship
species richness increases with area sampled
What does island species diversity show a strong negative relationship with?
distance from a source of species (the mainland or unfragmented habitat)
MacArthur and Wilson (1963)
plotted bird species richness and island area for a group of islands off New Guinea
Equilibrium Theory of Island Biogeography
the number of species on an island depends on a balance between immigration or dispersal rates and extinction rates
What assumptions come with the Equilibrium Theory of Island Biogeography?
-Island size controls extinction rates; populations on small islands have higher change of going extinct, due to small population size and increased effects of competition and predation
-distance from the mainland controls immigration rates; distant islands should have a lower rate than near islands
Simberloff and Wilson (1969)
manipulated mangrove islands in Florida by spraying with insecticides to remove all insects and spiders
Does the equilibrium theory apply to mainland areas?
-mainland areas have higher immigration rates because there are fewer barriers to dispersal
-Extinction rates are also lower because of continual immigration
-Species on mainlands will always have a good chance of being “rescued” from local extinction by other populations
What does habitat fragmentation create?
large edge effects at the transition between forest and matrix habitat
What can edge effects contribute to?
local extinctions
Why do we care about species extinction?
-ethical and aesthetic concerns
-loss of ecosystem services that sustain human health and well-being, such as food and medicines
