NRES 101

Possible reasons why more species occur near the equator
? More time without geological disruptions (e.g., glaciers)
? Competition among species is more intense
? Climatic stability
How does speciation normally occur?
Allopatric speciation (one population becomes separated into two or more)
What factors lead to speciation?
? Natural Selection
? Variation within a trait
? The trait provides a reproductive advantage
? Trait is heritable
? Sexual Selection
? Genetic Drift
Death of dinosaurs
cataclysmic event such as asteroid struck off Yucatan peninsula and caused drastic climate change wiping out 70% of life on earth
Pleistocene Changes
o Environmental changes (e.g. glaciers) lead to allopatric speciation
Death of the megafauna
? Overkill hypothesis
? Climate change hypothesis
? Disease hypothesis
? Meteor hypothesis
Recent Extinctions
o Current extinction rate is higher than the baseline rate
o Both rare and common species can go extinct
o Island Effect
Top 3 reasons for extinction
? Invasive species
? Hunting
? Habitat loss
How many species have gone extinct in Illinois over the last century
few
There are more ____ species than amphibians, reptiles, birds, and mammals combined
fish
Why are there so many freshwater species of fish given the relatively low amount of freshwater habitat?
Freshwater is easier to live in than saltwater and is generally warmer
What is the skeleton of sharks made of?
Cartilage

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