Chapter 21: Macroevolution and Speciation

why are there many different definitions used for species?

because speciation is a continuous process, and species are always changing due to evolution

why is defining species important?

1. we can better understand evolution and how new species have come to existence

2. by establishing species, we can better identify their properties and requirements (for conservation)

what are the four species definitions most commonly used?

1. Biological

2. Morphospecies

3. Ecological

4. Phylogenetic

what is the definition of the biological species concept?

species are groups of actually or potentially interbreeding populations that are reproductively isolated from other groups

what are the four limitations of the biological species definition?

1. how do we assess potential viable reproduction

2. reproductive isolation often takes a long time to develop

3. how does this apply to asexuallly reproducing species

4. some distantly related species can produce viable offspring

what is the definition of the Morphospecies concept?

members of the same species have similar morphological characteristics

what is an example of the morphological species concept?

three separate species of butterflies can identified by plotting differences in their antenna length and wing length

what is the definition of the ecological species concept?

two species with similar ecological niches cannot coexist in the same location at the same time. can be reworded as, two organisms are considered different species, if they occupy different niches

what is the definition of ecological niche?

habitat, recourses, and activity patterns of an organism within an environment

give an example of the ecological species concept

three different birds live in the same tree, but live and feed at different levels of said tree. Therefore each bird that lives at a different level of the tree, is a different species

what are two limitations of the ecological species concept?

1. if two organisms are genetically identical, but live in different niches, they are considered different species

2. organisms could be of the same niche, byt have zero genetic similarity but are considered the same species

which species concept best allows for differentiation of asexual organisms?

ecological species concept

what is the definition of the phylogenetic species concept?

members of the same species are descendants of a single common ancestor

what is the key limitation of the phylogenetic species concept?

all life on earth shares a common ancestor, so where do we draw the line/put a limit

how do we attempt to divide species using the phylogenetic species concept?

we base species on they common fate/common evolutionary path

what are the two main benefits of having multiple species concepts?

1. each concept emphasizes a different aspect of a continuous process

2. each one is better or worse suited for different biological systems (example would be sexual vs. asexual)

what is the definition of speciation?

divergence of two separate species when the populations become reproductively isolated and genetically distinct

1. one population to start, where individuals can freely move and mate

2. populations begin to differentiate, and two populations begin to form, due to some change (individuals can still potentially mate between the two populations)

3. populations become different species, gene flow has completely stopped, and there is no more interbreeding between populations

what are the two main types of reproductive isolation barriers?

pre-zygotic and post-zygotic

what is the definition of Prezygotic barriers?

barriers that prevent a zygote from forming (no fertilization of gametes)

what is the definition of postzygotic barriers?

fertilization occurs, but the offspring either do not survive to maturity or are sterile

what are the 5 main types of Prezygotic barriers?

1. geographical isolation

2. mechanical isolation

3. behavioral isolation

4. temporal isolation

5. gametic isolation

what is geographical isolation?

isolation caused by a geographic barrier (river, mountain, ocean)

what is an example of geographical isolation?

the isthmus of panama arose, separating populations of porkfish. although they each share characteristics with the other populations, they are actually different species because they cannot reproduce

what is mechanical isolation?

male/female genitalia are not compatible.

give an example of mechanical isolation

snails mate face to face, with their sex organ protruding from the right side. If the snails shells grow in opposite directions, they will be incompatible

what is behavioral isolation?

individuals select mates based on courtship rituals, songs, or other behaviors

what is temporal isolation?

when two or more species reproduce at different times, due to seasonal differences in mating or time of activity

what is gametic isolation?

sperm cannot fertilize the egg (caused by chemical interactions)

what are the two types of postzygotic barriers, and why do they occur?

hybrid inviability, and hybrid sterility. Occurs due to genetic incompatibility such as different numbers of chromosomes

What is hybrid inviability?

hybrid offspring does not survive to maturity

what is hybrid sterility?

hybrid survives but is sterile and cannot reproduce

what are the two main types of speciation?

allopatric speciation and sympatric speciation

what is allopatric speciation?

populations separated by geographical barriers that prevent populations from interbreeding

what is sympatric speciation?

populations are in the same geographical area, but gene flow has stopped between them

what are the two main types of allopatric speciation?

vicariance, and dispersal

what is vicariance?

occurs when a population is geographically divided by a physical barrier (e.g., mountains, rivers, glaciers) that prevents gene flow, leading to the evolution of separate species

what is dispersal?

when a subset of a population migrates to a new area, such as when individuals colonize an island, becoming isolated from the original population and evolving into a distinct species.

give an example of where natural selection has lead to sympatric speciation?

there are six species of anole lizards that started as one. all fed on insects but they occupied different vertical levels within the environment. lizards on the ground developed long legs to run, lizards in the trees developed short legs to climb. This led to the evolution of different species.