Biology 102_McGraw Hill_Ch24_origin of Species

Origin of Species and Macroevolution

Key Concepts:

Identification of Species

Mechanisms of Speciation

The Pace of Speciation

Evo-Devo: Evolutionary Developmental Biology

Identification of Species

Macroevolution

Evolutionary changes that create new species and groups of species

Concerns about the diversity of organisms established over long periods of time through the evolution and extinction of many species

Species

A group of organisms that maintains a distinctive set of attributes in nature

Currently, about 1.75 million species identified

Estimates of the total number of species range from 5 - 50 million

Difficulty in identifying a “species”

Subspecies

Ecotypes

Amount of separation time for two populations

Short time – likely to be similar and considered the same species

Long time – more likely to show explicit differences

May find situations where some differences are apparent but difficult to decide if the two populations are truly different species

Sometimes use subspecies classification

Characteristics that a biologist uses to identify a species will depend, in large part, on the species in question

Most commonly used characteristics are

• morphological traits,

• ability to interbreed,

• molecular features,

• ecological factors, and

evolutionary relationships

Physical characteristics of an organism

Drawbacks for determining species

How many traits to consider

Traits may vary in a continuous way; quantitative

What degree of dissimilarity to use

Members of the same species can look very different

Members of a different species can look very similar

Reproductive isolation

Prevents one species from successfully interbreeding with other species

Four main problems for determining species

•May be difficult to determine in nature

•Can interbreed and yet do not

•Does not apply to asexual species

•Cannot be applied to extinct species