evolutionary changes that produce new species and new groups of species
6 species concepts
1. biological species concept 2. morphological species concept 3. recognition species concept 4. cohesion (pluralistic) species concept 5. ecological species concept 6. evolutionary species concept
1. biological species concept
-based on reproductive isolation -populations of a species can interbreed or are interbreeding -members of a species are reproductively isolated from other species -this concept holds up well for animals, not so well for plants or bacteria
2. morphological species concept
-based on anatomical differences between species -similar to phylogenetic species concept -similar to paleontological species concept utilized to identify fossil species
phylogenetic species concept
descended from common ancestor; all members possess combination of certain defining traits
paleontological species concept
definition of species based on morphological differences known only from the fossil record
3. recognition species concept
distinct mating adaptations by species (molecular, form, behavior) -example: male peacock's tale
4. cohesion (pluralistic) species concept
-emphasizes factors that maintain the distinct form and behavior of a species -factors include such things as reproductive barriers
5. ecological species concept
species are identified by where they live and how they behave, not what they look like
6. evolutionary species concept
-emphasizes the evolutionary history of a species and the species' unique role in the environment -similar to the evolutionary lineage concept
evolutionary lineage concept
species are derived from a single distinct lineage and have their own evolutionary tendencies and historical fate
2 types of reproductive barriers
also known as reproductive isolation mechanisms 1. prezygotic barriers 2. postzygotic barriers
1. prezygotic barriers
impede reproduction and fertilization of the ova between species -5 barriers
5 prezygotic barriers
1. habitat isolation 2. behavioral isolation 3. temporal isolation 4. mechanical isolation 5. gametic isolation
2. postzygotic barriers
prevent the development of a viable, fertile offspring -3 barriers
3 postzygotic barriers
1. reduced hybrid viability (inviability) 2. reduced hybrid fertility (sterility) 3. hybrid breakdown
allopatric speciation
-occurs when a population becomes isolated from other populations and evolves into one or more species -involves geographical isolation
geographical barriers for allopatric speciation
can be almost anything lakes, oceans, rivers, mountain ranges, deserts, etc.
ring species
species arranged in a ring around a geographical barrier (allopatric speciation in progress)
allopatric speciation is more likely if
-the environment is different for the isolated populations -if an isolated population comes from a peripheral area -if the isolated population is small
adaptive radiation
a single ancestral species has evolved into a wide array of descendant species that differ in their habitat, form, or behavior
sympatric speciation
-occurs when members of a species that are within the same range diverge into two or more different species even though there are no physical barriers to interbreeding -in this form of speciation, the populations are not geographically divergent but become genetically divergent -polyploidy
an organism has more than two sets of chromosomes -new plant species can arise through this
polyploidy in an individual
formation of polyploidy offspring from two different species
each new species continuously evolves over long spans of time -the idea is that the large phenotypic differences that produce new species are due to the gradual accumulation of many small genetic changes
punctuation equilibrium
-the tempo of evolution is more sporadic -species exist relatively unchanged for many generations. during this equilibrium period, genetic changes are likely to accumulate (neutral changes), however, genetic changes that significantly alter phenotype do not substantially change the overall composition of a population
structures that have evolved under one context can later take on other functions. example: stress sensors have evolved into hearing organs in some insects