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..