Generalist and Specialist Species:
Broad and Narrow Niches• Generalist Generalist
species species tolerate a tolerate a wide range of wide range of conditions.conditions.
• Specialist Specialist species can species can only tolerate only tolerate a narrow a narrow range of range of conditions.conditions.
Is it better to be a Generalist or a Specialist?
Is it better to be a Generalist or a Specialist?
Answer: It depends.
Speciation, Extinction, and Biodiversity
Speciation, Extinction, and Biodiversity
Speciation - formation of Speciation - formation of two species two species from onefrom one species because of species because of divergent divergent natural selectionnatural selection
1)1)Geographic isolation – groups Geographic isolation – groups of the same species become of the same species become physically separatedphysically separated
Geographic Isolation
…can lead to reproductive isolation, divergence of gene pools and speciation.
Speciation, Extinction, and Biodiversity
Speciation, Extinction, and Biodiversity
2)2) Reproductive Isolation – isolated Reproductive Isolation – isolated populations become so populations become so genetically different they genetically different they cannot . . . cannot . . .
Interbreed, orInterbreed, orproduce live, fertile produce live, fertile
offspringoffspring
Extinction: Lights Out
• Extinction occurs when the population cannot adapt to changing environmental conditions.The golden toad of Costa The golden toad of Costa
Rica’s Monteverde cloud Rica’s Monteverde cloud forest has become extinct forest has become extinct because of changes in because of changes in climate.climate.
Extinction: Lights Out
•99.9 % of all species that ever existed are now extinct
Tertiary
Bar width represents relative number of living speciesEra Period
Species and families experiencing
mass extinction
Millions ofyears ago
Ordovician: 50% of animal families, including many trilobites.
Devonian: 30% of animal families, including agnathan and placoderm fishes and many trilobites.
500
345
Cambrian
Ordovician
Silurian
Devonian
Extinction
Extinction
Pal
eozo
icM
eso
zoic
Cen
ozo
ic
Triassic: 35% of animal families, including many reptiles and marine mollusks.
Permian: 90% of animal families, including over 95% of marine species; many trees, amphibians, most bryozoans and brachiopods, all trilobites.Carboniferous
Permian
Current extinction crisis causedby human activities. Many speciesare expected to become extinctwithin the next 50–100 years.Cretaceous: up to 80% of ruling reptiles (dinosaurs); many marine species including manyforaminiferans and mollusks.
Extinction
Extinction
Triassic
Jurassic
Cretaceous
250
180
65Extinction
ExtinctionQuaternary Today
Extinction• Background extinctionBackground extinction
– Normal extinctionNormal extinction of various species as of various species as a result of changes in local a result of changes in local environmental conditionsenvironmental conditions
• Mass extinctionMass extinction– extinction resulting from extinction resulting from catastrophic, catastrophic,
wide-spread eventwide-spread event in which large in which large groups of existing species are wiped outgroups of existing species are wiped out
• Adaptive radiationAdaptive radiation– Process in which numerous new species Process in which numerous new species
evolve to evolve to fill vacant and new ecological fill vacant and new ecological nichesniches in changed environments in changed environments
Period of Recovery Following Extinction
Adaptive radiation -Adaptive radiation -
Process in which numerous Process in which numerous new species evolve to new species evolve to fill fill vacant and new ecological vacant and new ecological nichesniches in changed in changed environmentsenvironments
How do speciation and extinction affect
biodiversity?
Speciation – Extinction = Speciation – Extinction = BiodiversityBiodiversity
Extinctions and depletions temporarily Extinctions and depletions temporarily reduce biodiversity YET create reduce biodiversity YET create
evolutionary opportunitiesevolutionary opportunities for surviving for surviving species to undergo species to undergo adaptive radiationsadaptive radiations
to fill unoccupied and new biological to fill unoccupied and new biological nichesniches
Effects of Humans on Biodiversity
• The scientific consensus is that The scientific consensus is that human activities human activities are decreasing the earth’s biodiversityare decreasing the earth’s biodiversity..