Lecture 14: What is a species? (Exam 3)

Question 1

strengths and weaknesses of the biological species concept

Answer 1

• species are groups of interbreeding individuals that mate and form fertile offspring, but…
• what about asexual species like archaea and bacteria?
• what about fertile hybrids like plant species?

Question 2

Two important (and separate) considerations in defining “species

Answer 2

1. are species entities that actually exist in nature?
2. if “species” exist, can we provide a formal definition that allows for identification and study?

Question 3

what speciation is and broadly how it occurs

Answer 3

• a continuous process
• over many generations, one population diverges to become separate populations that no longer interbered
• for ecological/geo/behavioral/genetic reasons, a population of interbreeding organisms stops/breeds less, resulting in immediate/eventual genetic/mechanical incompatibilities or reduced hybrid fitness, producing separate species

Question 4

Three geographic modes of speciation

Answer 4

allopatric, parapatric, sympatric

Question 5

allopatric speciation

Answer 5

• barrier is formed (ocean, mountains, continents moving)
• leads to inisolation
• possibly most common?

Question 6

parapatric

Answer 6

• population splits off into new niche, become less like the old population

Question 7

sympatric speciation

Answer 7

• new species evolves from a single ancestral species while inhabiting the same geographic region
• within the same population

Question 8

Why we need a species definition and why that’s complicated

Answer 8

• how do we classify common ancestry?
• how do we determine the mechanisms in which one species becomes two
• how do we quantify the current biodiversity on earth?
• complicated because “do species exist” is different than can “species be reliably and empirically diagnosed”

Question 9

All types of reproductive isolation and how each can lead to divergence

Answer 9

• premating
• postmating, prezygotic
• postzygotic

Question 10

premating reproductive isolation

Answer 10

organisms are unable to mate at all

Question 11

postmating, prezygotic

Answer 11

organisms can mate but no zygote is produced (no fertilization)

Question 12

postzygotic

Answer 12

a zygote is produced but viability or fertility of hybrid offspring is poor

Question 13

premating barriers

Answer 13

• geographic isolation (physical)
• temporal isolation (diff mating season)
• behavioral isolation
• ecological isolation (habitat preferences, pollinator shifts)

Question 14

post-mating barriers

Answer 14

1. incipient species
2. secondary contact
3. selection against hybrids
4. speciation

Question 15

unified species concept

Answer 15

• one concept can’t rule all species; there is a biological reality
• we argue the grey zone