Lecture 21-22 (Case Studies) Flashcards
What are typical island chain formation processes?
Subduction zones: results in the upwelling of magma.
Diverging regions of tectonic plate formation: weakness in the crust allows for magma penetration to the surface
- Example: the Galapagos islands
How were the Hawaiian islands formed?
Formed by plate moving over a hot spot (magma column)
Plume stays in one place while plate moves –> that is why it is a chain of islands rather than one big island
- islands very in age
- big island is right over hotspot (very active)
New islands still forming in the Hawaii chain as the plate moves over the hostpot
How is an atoll formed?
Happens after the loss of volcanic activity
Soil erosion from rainfall is no longer being offset by new land added through volcanic activity.
Landmass will erode into surrounding marine envr.
As sediment erodes, it creates shallow sea shelves for coral growth
Coral reef surrounding the island grows as terrestrial land erodes
Eventually, all that remains is the coral ring
What native species were the most and least abundant?
Most: flowering plants, insects
Least: amphibians and reptiles (none), only 2 native mammals (bats and seals)
What are some hypotheses as to why there are few native mammals in Hawaii?
Never got there to being with (probably what happened)
Got there, but conditions were wrong (could not support their niche)
Got there, but then got outcompeted
What are options for dispersal of organism to Hawaii?
Ocean dispersal
Aerial dispersal
Avian dispersal (on a bird, through them eating stuff, of stuff sticking to them)
Why are there fewer founder species than the number of species nowadays?
Due to adaptive radiation
How can we determine ancestry of species in from Hawaii?
Genetic analysis: links extant species from Hawaii to extant mainland species
Can also compare fossilized samples
Why are so many founders in Hawaii from Asia?
The jet stream can transport spore, small seeds, insects, and flying animals across the ocean (atmospheric process)
- Powerful winds in the upper atmosphere of the planet
- Involved in global weather patterns
- Can also pick up hitchhikers
- Many endemic Hawaiian linages are small enough to be caught in the wind, or fly
Some terrestrial species have specialized mechanisms which allow for air travel
What biotic factors contributed to existing species and trait diversity in Hawaii?
Random genetic drift
Founder effect
Population size
What abiotic factors contributed to existing species and trait diversity?
Climate heterogeneity
Open niches
What are the patterns of evolution in island populations?
Mutation introducing new phenotypes and alleles
Sexual selection
Coevolution
Natural selection
Genetic drift
What is random genetic drift?
Small populations can change gradually over time, even when not under selection pressure
Based on statistics and probability
Can lead to genes being lost from population or genes becoming very prominent
Since nothing in the envr. is selecting for one allele over the other, inheritance is completely random.
If two populations of the same species are isolated, genetic drift can eventually result in completely different species –> speciation
- sub-populations can also gain new mutations or lose previous alleles
What is the Founder effect?
New population colonizing an island = Founder population
Smaller than source population
- evolution happens sometimes faster in a small population (a mutation can spread faster in smaller vs. larger population)
Contains only a sub-set of the genetics of the original pop.
May also have harmful recessive founder mutation
What is environmental heterogeneity?
Diverse range of different climatic conditions
Greater diversity of different abiotic climatic conditions = greater diversity of niches
Often leads to a greater diversity of species to fill those niches
What is the rain shadow effect?
The side of a mountain where air rises from ocean and cools/condenses is much humid since it has more precipitation, therefore more vegetation.
Once the air package reaches the peak, it expands and warms. The other side of the mountain is dry and hot.
What is an open niche?
Resources available for species which can adapt to take advantage of those resources
- No things that eat birds (no snakes, rats, mammals, etc.)
- Also less competition for food (seed and insect eaters)
What happens when a niche opens up in island habitats?
Often fewer species available to fill typical species niches in an environment
- May lead to unique traits in unexpected species
Typical niches common in many environments
Apex predator: often mammals on continents
- canids, felidae
Large grazing herbivore: also often mammals on continents
- deer, elephants
However, there are almost no mammals on Hawaii
What is an abiotic niche (fundamental niche)?
Physical conditions under which a species can survive (climate, precipitation, etc.)
What is a biotic niche?
Ecological interactions (predator/prey interactions, competition, diseases, food sources, etc.)
What is the main grazer of Hawaii?
Ducks
Some lineages evolved tooth like shapes to the beak
- thought to allow for more efficient grazing
What influences evolution on Hawaii?
Genetic characteristics of a founder population
Heterogeneity of the environment
Open biotic niches –> has resulted in multiple adaptive radiations in founder species
Why are there many different species of honeycreepers on Hawaii?
Founder species: Eurasian rosefinch
Arrived before all the islands had formed –> blank slates
Adaptive radiation –> filled many niches
Why are islands especially vulnerable to invaders?
Loss of defenses: species have evolved with the absence of predators
- lack of large predators on islands can also result in changes in island species
- no reason to maintain energetically expensive defenses if there are no more predators to defend yourself from –> leads to the loss of defenses compared to mainland counterparts.
Vulnerability to novel pests/pathogens
- absence of many pest and pathogen lineages present in the home ranges of invasive species (open niches that can be filled)
How to control invasive species?
Biocontrol
How do disturbance cycles contribute to diversity on Hawaii?
Many islands still volcanically active –> cycle of destruction from lava flows and regrowth
- Volcanic activity is destructive in the short run, but provides land area and minerals for plant growth in the long run.
Age of island also influences terrestrial and marine ecosystems –> nutrient availability in both systems changes over the life of an island
- Soils eroded to ocean brings minerals to marine environments
- As terrestrial biodiversity decreases, marine biodiversity increases
What happens after a lava flow?
Complete destruction of existing flora and any fauna which is not able to move out of the way
Mineral rich substrate remains after lava flow
Lichens, ferns and mosses begin to colonize the volcanic substrate
- seed plants in cracks
- contributes to soil formation –> gives rise to more plants
Explain the evolution of biomass with time after a volcanic eruption
At the beginning, nutrients are locked in rocks
- not a lot of vegetation
As more plants begin to colonize the substrate, promotes soil formation and the growth of more vegetation
- plants begin to grow and replete with new nutrients
At the peak, soil is fertile and breaks down with weathering
Biomass begins to decline toward the end since nutrient supply is exhausted
What are the characteristics of the Isthmus of Panama?
Dry land connection between North and South America (3 million years ago)
First complete link between the Americas since the breakup of Pangea
Physical changes included tectonic movements, ocean circulation, climatic change
How did the Caribbean plate tectonics move to create the Isthmus of Panama?
Smaller plates buffered the collision (multiple plates moving in different directions)
Formation of isthmus occurred gradually
How did ocean circulation change after the creation of the Isthmus?
Circum-tropical circulation of warm water is blocked
Warm current deflected north in Atlantic (Gulf Stream)
Gulf Stream deflects Labrador Current
Humboldt Current flows north on Pacific side.
Before, the ocean circulation had 3 passages (any precipitation could fall in warm areas as rain)
After, warm circulation/current gets forced upwards and creates the Gulf stream
- Have warm and cold bodies meeting further north
- Precipitation has much higher chance of falling as snow –> can create glaciation
What are the implications of circulation change after the creation of the Isthmus?
Increased temperature difference between warm Caribbean/Gulf of Mexico and cool Pacific
Deflection of Gulf Stream increases moisture in northern latitudes
How do we know that Panama was an island?
Islands are dry land
Dry land is surrounded by shallower water
Evidence for shallow water in past
Fossil remains of many species of shallow water in sediments in Caribbean
- Can date these fossils to see when shallow water existed
What were the direct effects of the formation of the Isthmus of Panama on biological systems?
Land bridge as barrier to dispersal for marine organisms
Land bridge as a corridor for dispersal for land organisms
What were the indirect effects of the formation of the Isthmus of Panama on biological systems?
Climatic changes
Geological changes lead to subsequent changes in distribution
- ecology
What is the evidence of when the Isthmus closed?
As soon as Isthmus closed, wind that was blowing across pushed water away on the Pacific side
- pulled water in from deep and brought up nutrients (trade winds, upwelling and nutrients)
- can draw inferences with fossils associated with this (fossils and shell formations)
What are the characteristics and impacts of the Isthmus as a barrier?
Isolation of populations of marine invertebrates
Related species in several groups isolated across isthmus
- ex. snapping shrimp, marine snails, foraminiferans
–> leads to speciation because there are different environmental conditions (accumulation of genetic differences, phenotypic differences)
What are the ecological differences between the Pacific side and Caribbean side of Panama?
Pacific:
- water is much deeper
- periodic upwelling
- very fast moving pelagic productive system (due to high nutrient availability)
Caribbean
- caribbean and atlantic plate makes more shallow and protected water
- lower in available nutrient content
- more coral reefs
- interactions between abiotic and biotic (biotic created new environmental conditions for new organisms)
Divide production vs. construction, high vs. low nutrient content, and pelagic vs. corals/mangroves/seagrass – between pacific and carribbean
Pacific:
- production
- high nutrient content but sporadic
- pelagic
Caribbean:
- construction
- low nutrient content
- corals, mangroves, seagrasses (slow growing, then creates additional habitats and protection/stability)
What are a major consequences of the isthmus as a corridor?
the great american biotic interchange
What was the pre-link fauna like?
Both continents had diverse fauna of large mammals, birds, etc. filling all the usual terrestrial niches
- large and small predators
- large herbivores - grazers and browsers
- small herbivores
- scavengers
Savanna, grassland, forest specialists
Why were the species filling niches in North America almost entirely different than the species filling niches in South America?
They were separated for a long time –> no gene exchange, have entirely different organisms evolving in parallel in these different areas
All of the different type of niches were filled by animals with similar kind of traits (convergent evolution)
Even though genetic pathways (and evolutionary history) is completely different, selective pressure creates similar traits
What is convergent evolution?
Unrelated species subject to similar environmental and ecological conditions
Selection pressures drives evolution in similar directions
Species come to resemble each other
Many examples in North and South America prior to connection
- saber-toothed cats in North vs. saber-toothed marsupials in South
- Camels in North vs. lipopterns in South (large browsers)
- Rhinos in North vs. toxodontids in South (large grazers)
Heralds and legions
Successive waves of interchange
Heralds: early colonizers (island hopping)
Legions: mains invasion group (walkers and crawlers)
What are the legions of the North?
(moved south) Shrews, rabbits, mice, squirrels, bears, horses, etc…
- Many of these later became extinct in the North
Several carnivores also moved south
Large cats and dogs –> both families are now more diverse there than anywhere
Many North American groups became quite diverse in South America
- Some became extinct during Pleistocene
Legions of the South
Animals moving from South to North
armadillos, sloths, capybaras, manatees, etc.
Phorusrhachid
Large flightless predators
Dominant in South American savannas
Later dispersed to North America
Range of sizes and habits in South America
What was the aftermath of the exchange?
At least 50% of South American mammals are descendants of ancestors that came from North America
Several extinctions in South American mammal fauna
- competition, predation
Birds, reptiles, amphibians not as affected
- South American birds unique - high diversity and endemism
- few shared reptiles or amphibians
What are some recent exchanges happening across North and South America?
Several groups have continued to move across isthmus since first establishment
Diverse in one continent, with few species on other side of isthmus
Southern groups: iguanas, hummingbirds
Northern groups: salamanders
What are some new barriers?
Flora and fauna of North and South America are still quite distinctive
Replacement of the physical barrier (salt water) with an ecological barrier
What is the current vegetation in Northern South America and Eastern Central America?
Rainforest, cloud forest
What is the current vegetation in Western Central America, southern USA?
Desert and shrub forest
What are human changes made to the Isthmus of Panama?
No longer a complete barrier –> Panama Canal connects Atlantic to Pacific
freshwater vs. saltwater –> freshwater barrier to marine organisms (26 m above sea level)
- ships move into freshwater through locks
- 200+ million liters of freshwater used up per ship –> a LOT of water (although it is recycled, it becomes very saline)
What are the side effects of the Panama Canal?
Rainforest produces more water than developed land
Buffer zone of protected land on either side of canal provides freshwater, but also protects habitats and species
Increasing pressure for crops, development
Widening canal requires bigger drainage area
