AP Biology Chapter 22: Key Terminology

Speciation

reproductive isolation

the existence of biological factors (barriers) that impede members of two species from interbreeding and producing viable, fertile offspring.

hybrid

offspring that result from an interspecific mating

prezygotic barriers

(before the zygote) block fertilization from occuring

postzygotic barriers

(after the zygote) if a sperm cell from one species overcomes the prezygotic barriers and fertilize an ovum from another species

biological species concept

species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring

what is the importance of gene flow to a population?

according to a population, gene flow holds a population together

what can contribute to speciation according to the biological species concept?

reduction or lack of gene flow in a population

what are some limitations of the biological species concept?

cannot be used to evaluate the reproductive isolation of fossils or organisms that reproduce asexually most of the time

morphological species concept

distinguishes a species by body shape and other structural features

what are the weaknesses and strengths of the morphological species concept?

strengths: it can be applied to asexual and sexual organisms, and can be useful without information on the extent of gene flow; weaknesses: relies on the subjective criteria that researchers may disagree on in terms of which structural features distinguish a species

ecological species concept

defines a species in terms of ecological niche, the sum of how members of the species interact with nonliving and living parts of their environment

name key concepts in the ecological species concept

the ecological species concept can accommodate sexual and asexual reproduction, and emphasizes the role of disruptive natural selection as organisms adapt to different environments

phylogenetic species concept

defines a species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life

list properties of the phylogenetic species concept

by tracing morphology and molecular sequences, biologists can distinguish groups of individuals that are sufficiently different to be considered separate species. but the difficulty of the concept comes from determining the degree of difference required to indicate separate species

allopatric speciation

gene flow is interrupted when a population is divided into geographically isolated subpopulations

sympatric speciation

speciation that occurs in populations living in the same geographic area

what factors can cause sympatric speciation?

polyploidy, habitat differentiation, and sexual selection

polyploidy

an accident in cell division that results in an extra set of chromosomes

autopolyploid

an individual that has more than two chromosome sets that are all derived from a single species

allopolyploid

a hybrid from two different species that is fertile when mating with each other but cannot interbreed with either parent species; therefore representing a new biological species

habitat differentiation

when a subpopulation exploits a habitat or resource not used by the parent population

list the prezygotic barriers in reproductive isolation

• habitat isolation

• temporal isolation

• behavioral isolation

• mechanical isolation

• gametic isolation

habitat isolation

when two species live in different habitats, preventing them from meeting and mating, even if they live in the same geographical area

temporal isolation

the difference in the timing of critical reproductive events that prevent closely related species from mating and producing hybrid offspring

behavioral isolation

differences in behavior, particularly mating rituals, prevent members of different species from interbreeding

mechanical isolation

when the reproductive organs of two species are incompatible, making it physically impossible for them to mate

gametic isolation

when the sperm of one species fails to fertilize the eggs of another species, even if mating occurs

list postzygotic barriers

• reduced hybrid variability

• reduced hybrid fertility

• hybrid break down

reduced hybrid variability

phenomenon when an offspring’s fitness is significantly lower than those of their genetically distinct parents, which prevents them from maturing into healthy adults

reduced hybrid fertility

phenomenon when hybrids are viable but sterile, meaning they cannot produce their own offspring

hybrid break down

phenomenon when the first generation of hybrid offspring are viable and fertile, but produce subsequent generations are not

punctuated equilibrium

describes periods of apparent stasis punctuated by sudden change, and once species are established, the rate of change slows; gene flow must be interrupted in order for this process to begin