BIOL 3445 Lecture Notes - Lecture 23: Species Problem, Reproductive Isolation, Metapopulation
BIOL 3445.001 | Lecture #23 | 4/10/2018
Speciation
ANNOUNCEMENTS
➢ Exam #3
o Study guide and practice quiz on Canvas
o Next Thursday (04/19/2018)
OBJECTIVES
― Explain why “species” are so hard to define
― What is the biological species concept?
― Describe how a speciation event might happen
― Understand the different ways that species may be reproductively isolated
― Explain the differences between allopatric and sympatric speciation models
WHAT IS A SPECIES?
― “Trying to define the undefinable” – Darwin
― At what point do species diverge enough to be considered separate?
― The idea of “species” is a useful concept for us
o Allows us to categorize and organize creatures
o Helps us to identify different organisms
― It is not always easy to decide what exactly defines a species
― We’re trying to confine nature to a man-made concept
― GROUP WORK:
o Why is it so hard to figure out which populations might actually be
separate species?
▪ It can be difficult to determine what makes species different
▪ Maybe some populations could interbreed but never interact
▪ Some species have different chromosome differences causing
them to look similar but have very different molecular layouts
▪ Can look very different in different seasons of life
find more resources at oneclass.com
find more resources at oneclass.com
BIOL 3445.001 | Lecture #23 | 4/10/2018
o Why is the idea of “species” a useful concept for us?
▪ Helps us understand how one population changes into another
population over time (evolution)
― Key vocabulary to understand the concept of species
o Phylogenetic Species Concept: species are defined as the tips of
branches on a phylogeny
o Biological Species Concept: species are defined as groups of actually (or
potentially) interbreeding populations which are reproductively isolated
from other groups
▪ Could they? Would they? Should they?
o General Lineage Species Concept: species are populations, sharing
genes, that evolve together as a unit
― In general, species concepts recognize:
o Gene flow occurs within the populations of a species
▪ Those populations all experience some of the same effects of
evolution
o A species evolves together as a metapopulation
▪ Even though Asian Elephants in zoos are isolated from each other,
they are the same species
o Different species evolve as separate units
KEEPING SPECIES APART
― Isolating barriers that block gene flow are required to keep sexually reproducing
species separated
o They would if they could, but they can’t
o Physical barriers (mountain ranges, oceans, etc.)
o Reproductive barriers (genitalia, mating rituals, etc.)
― Allopatry (geographic barriers): populations are prevented from interbreeding
due to geographical separation
o Examples: mountain ranges, oceans, rivers, land
o So, physical separation is one way that species may form, but what keeps
them separated when geographical barriers are removed?
― Often, allopatry is not enough to define species
o They must also somehow not be able to reproduce successfully when
brought together
o Allopatry may be the beginning of some speciation events, but
populations must evolve intrinsic barriers to interbreeding before
becoming separate species
― Example: Elk vs Red Deer
o Red Deer are native to Europe and are closely related to N. American Elk
o The land bridge went away thousands of years ago and separated them
o Though they’ve been separated for thousands of years, they can still
interbreed and produce viable offspring
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Exam #3: study guide and practice quiz on canvas, next thursday (04/19/2018) Explain why species are so hard to define. Describe how a speciation event might happen. Understand the different ways that species may be reproductively isolated. Explain the differences between allopatric and sympatric speciation models. Trying to define the undefinable darwin. The idea of species is a useful concept for us: allows us to categorize and organize creatures, helps us to identify different organisms. It is not always easy to decide what exactly defines a species. We"re trying to confine nature to a man-made concept. Biol 3445. 001 | lecture #23 | 4/10/2018: why is the idea of species a useful concept for us, helps us understand how one population changes into another. Should they: general lineage species concept: species are populations, sharing genes, that evolve together as a unit. In general, species concepts recognize: gene flow occurs within the populations of a species.
