Biogeography Flashcards
evolutionary history
when and where did a species originate, and what has changed since then?
influenced by geological history: we can observe the current species distribution to infer the influence of geographic and geological events
discovery of biogeography
- Wallace’s observations were the foundation for the modern, wester, english-language study of biogeography
- remarkable patterns of species distribution in the Malay Archipelago could not be explained by geology or climate
- Walter deduced that differences had to do with the depth of the water separating the two regions
biogeographic regions
- Earth can be separated into biogeographic regions that contain characteristic species assemblages
- boundaries occur where species composition changes dramatically over short distances
- the regions have or had barriers that prevent dispersal
plate tectonics
major factor controlling the formation of biogeographic regions
during the Triassic and Jurassic ages, Pangea rifted apart to form Godwana and Laurasia, which then rifted apart to form modern day continents
fossils
- help to reconstruct plate tectonics position over time
- an organism that is present in two or more continents probably descended from an ancestor that was present in Pangea
- help us tell where a tectonic plate used to be and also the age of the lineage
geographic isolation
results from biogeographic processes
evolutionary separation of species can be attributed to two process:
vicariance and dispersal
vicariance
a barrier that prevents dispersal formed and divides a species into two or more discontinuous populations
lineage present BEFORE barrier
North American fish
- ancestor of each species was present in the original body of water - - Pleiostone glaciation separated the epicontinental seaway and led to geographic isolation
- the split of the two lineages was due to the split of the body of water
dispersal
- members of a species moved across an existing barrier to create a new population elsewhere
tiger chamelons
tiger chamelons are found on the Seychelles Island, but their most common ancestor is present on the mainland of Africa
the species diverged 38 million years ago, but the Seychelles were present before that
We can observe biogeography…
by looking at modern day distribution of species
Southern beech trees are observed across the Southern hemisphere; their common ancestor was likely distributed across Godwana
therefore, vicariance led to modern distribution
biodiversity rate
biodiversity follows a latitudinal gradient - diversity is higher near the tropics than higher latitudes
reverse for some groups - seabirds
species diversification rate
speciation rate is higher and the extinction rate in the tropics is lower due to the larger geographic area and a warmer, more stable climate
species diversification time
amount of time for speciation is greater in the tropics because that region has been climatically stable for longer
productivity
diversification is prompted by higher productivity, which allows species more resources and decreased risk of extinction due to less competition
explains seabird hypothesis
island biogeography
pertains to islands or island-like habitats (isolated area surrounded by dissimilar habitat)
island size
larger islands will have more species due to the species-area relationship
on smaller islands, there are less resources available which leads to increased competition, increasing the rate of extinction
immigration source
islands show more species the closer they are to a source (mainland/large island)
the farther the island is from the source, the less likely a new species will reach it
island biogeography graph
- biogeography explains the balance between island size and distance from other landmasses in determining biodiversity
- the number of species present on an island is a balance between the rate at which species immigrate to the island and the rate at which resident species become extinct
- even though species come and go over time, the turnover will always results in an equilibrium amount of species
habitat fragmentation
- isolated patches of suitable habitat surrounded by extensive areas of unsuitable habitat
- human activities are fragmenting many biomes on Earth, turning them into island-like habitats
edge effects
fragmentation exposes species to many potential hazards: fires, predators, diseases, hunting species, and invasive species
edges of the fragment are less hospital, reducing the effective space of the fragment
reduces immigration rate between patches
Amazon Rainforest
researched measured biodiversity in different sized islands of forest surrounded by deforested areas
smaller islands have fewer species
the “ocean” between fragments can be very narrow - 80 meters is enough to cause isolation and species loss
