4.3 How Species Form In this section, you will: Explain ways in which species can become reproductively isolated Describe how new species form Compare two models that explain the rate of evolution How Species Form Biological species- consists of populations that can interbreed and produce viable offspring Different species in same habitat remain different species due to reproductive isolation Why might members of the same species not be able to interbreed? Reproductive Isolation Species are reproductively isolated from other species This can be due to a number of different factors: 1
Speciation- Interbreeding Prevented Geological Barriers- physical separation Ex. Mountains/Rivers Ex. Galapagos Islands Biological Barriers- reproductive isolation Ex. Behaviors (bird or frog song) Ex. Pheromones (spider mate attraction) No contact because of location/resources Forming New Species There are two general pathways that can lead to the creation of a new species 1. Transformation New species gradually develops as a result of mutation and adaption to changing environmental conditions. Old species is gradually replaced. Ex. Ancestral mammoth to steppe mammoth to the wooly mammoth What does this do to biological diversity? - Unchanged Species Formation 2. Divergence- one or more species arise from a parent species Ex. Of adaptive radiation What does this do to biodiversity? Increases- because the number of species increases Isolation of Populations A single founder species can produce number of different species Speciation to occur- species must be prevented from breeding Must be biological or geographical barriers Separated for a long period of time- change occurs through natural selection 2
Adaptive Radiation Adaptive radiation is the diversification of a common ancestral species into a variety of differently adapted species Why Does Adaptive Radiation Occur? Offspring disperse- encounter new environments with slightly different selection pressures The adaptations that allow organism to survive in new habitats result in new species The Speed of Evolution How fast is evolutionary change? Evolutionary biologists have suggested evolution is very slow Gradualism Large differences we see between species now- sum of all of the small changes over a long period of time However, sudden changes seen in fossil record do not support this claim A New Idea Punctuated Equilibrium Punctuated equilibrium - evolutionary history consists of long periods of little changebroken by rapid change When species first diverges from a parent, major morphological changes occur New selection pressures select for different adaptations Result- in the next generation being quite different 3
Gradualism vs. Punctuated Equilibrium Summary The Theory of Evolution by Natural Selection 1. Life forms have developed from ancestral species. 2. All living things are related to on another by varying degrees through common descent. 3. All living things on Earth share a common origin (or ancestor) http://palaeo.gly.bris.ac.uk Summary The Theory of Evolution by Natural Selection (Continued) 4. The mechanism by which one species evolves into another involves random heritable genetic mutations. Mutations that increase the survival advantage of an individual will most likely be passed on to offspring. Over time the successful mutation spreads throughout the population and causes a change in the population Where Do We Go From Here? There is still wide debate over evolutionary theories Much research is being carried out to refine these hypotheses New discoveries will further the development of these theories over time 4
Read Section 4.3 #1-5 pg. 142 Homework 5