Name:______
Date:______
Lesson # 7: Evolution
(Processes and Patterns of Evolution)
Evolutionary Change via Selection
Types of selective pressures may result from: i.e. climate conditions, food availability, predators, and choice of mate etc.
There are four types of selection:
1) Directional Selection
-Favours an ______in the value of a trait from the current population average
-Occurs when the environment favours one ______trait
-Causes average to move in one direction, the average has moved to one extreme
-The result is a ______away from the average
-Often happens when environment changes in a ______way
Examples
Fishing with nets
Hummingbirds using their bills to feed on nectar
-Very common in artificial selection… why?
-How would necks of giraffes or camouflage / mimicry help explain directional selection?
2) ______Selection
-Selection against individuals exhibiting traits that ______from the current population average
-The most ______trait is the favoured trait
-Most common form of selection
-Once a species adapts to its environment, selective pressures maintain the evolved ______
Example
-Human birth weight
-Medium sized hummingbird bill length
What other examples can you think of?
3) Disruptive Selection
-Selection that favours ______or more variations of a trait that differ from the current population average
-Favours traits at both ______
-Causes species to diverge
-Occurs when two different types of resources are in ______area
-May lead to formation of new species
Examples
-(e.g., Darwin’s finches – small beaked ate small seeds and big beaked ate large seed; yet, medium beaked could not eat or compete for either seed size (unfavourable))
4) Sexual Selection
-Favouring of any trait that specifically ______the mating success of an individuals
-Often leads males and females of a species evolving appearances and behaviours that are quite different from each other
-Most common behaviour is the female selects male, and the males compete one against one another
-Most females choose mates based on ______
-Some traits, while sexually ______are detrimental
Examples
-Bright coloured feathers of a male peacock is attractive for females but easy for predators to see
-A very successful male elephant seal may mate with dozens of females each year and hundreds of females in his lifetime, while a weak male may live a longer life but produce no offspring. In this case, the genes of the short lived but dominant male are destined to become more common in succeeding generations
Evolutionary Change Without Selection
-Not all evolutionary changes are the result of natural selection
-Sometimes there are changes in the genetic makeup of a population that are not influenced by the traits of individuals
-Each of these changes tends to reduce genetic diversity within a population
Types of Evolutionary Change Without Selection
1)Genetic Drift
-The ______makeup of a population can change simply by chance
-The ______shifting of the genetic makeup of the next generation
-The smaller the number of individuals in a population, the greater the ______of genetic drift
-In small populations, genetic drift can result in a particular allele becoming either very common or disappearing entirely over a number of generations
-Any lost alleles result in a reduction of genetic diversity of the population
2) Bottleneck Effect
-A ______in genetic diversity following an extreme ______in the size of a population
Example
-If an individual population of 10,000 individuals is reduced to only 50 individuals, they are unlikely to contain all of the traits found in the larger population
-Many traits, and in particular rare ones are likely to be eliminated
-If the population is allowed to ______the genetic makeup of future generations will be ______to the traits carried by those 50 surviving individuals and any new mutations
3) ______Effect
-Occurs when a small number of ______establish a new population
-The new ______will begin with a different ______than the original mainland population’s gene pool
4) The ______Principle
-In the large populations in which only random ______is at work, allele frequencies are expected to remain ______from generation to generation
-Based on the Hardy – Weinberg principle, biologists recognize that the following conditions result in evolution:
Natural selection – favours the passing on os some alleles over others
Small ______size – increases the likelihood of genetic drift
Mutation – introduces new alleles to a population
______or emigration - introduces or removes alleles in a population
Horizontal gene transfer – the gaining of new alleles from different species
Patterns of Evolution
-Natural selection leads to predictable outcomes
1)Adaptive ______
-Occurs when a ______species evolves into a number of distinct but closely related species
-Each new species fills a different ecological niche
-This process usually occurs when a variety of new ______become available (and are not being used by other species)
-Only real competition is with each other
2) Divergent ______
-In any ecosystem, there are a number of ecological niches
-This is the ______evolution of a group into many different forms
-______of differences between groups which can lead to the formation of new species (great______of species)
Example
-Ontario forests have over 20 species of closely related rodents including deer mouse, flying squirrel, porcupine and beaver
-All which evolved from a single common ancestor
3) ______Evolution
-Occurs when two ______species, evolve to occupy similar ecological niches
-When two different species have evolved similar traits in the same ecological niche
Examples
-Cacti and euphorbia
4) Coevolution
-A process in which one species evolves in ______to the evolution of another species
Example
-Certain plants have evolved hard protective ______to protect their seeds, while some seed – eating mammals have evolved powerful jaws and teeth for ______through hard shells
-Any seeds surrounded by a hard shell might be better ______from herbivores and better able to survive than seeds with thin shells
-Similarly, any herbivore with a slightly more powerful jaw might be able to ______more food than an herbivore with a less powerful jaw.
-This is sometimes called an ______
Struggle between competing sets of co-evolving genes, traits, or species, that develop adaptations and counter-adaptations against each other, resembling an arms race