# Chapter 4: Evolution

• Genetic change in population of organisms across generations
• Genetic change often leads to modifications in appearances, functioning, or behaviour of organism through time
• Mechanism of evolution
• Mutation
• Migration
• Random drift
• Natural selection: traits that enhance survival and reproduction are passed on more frequently to future generations than those that do not

#### Charles Darwin

• Proposed the concept of natural selection

Descent with Modification - Traits are passed on from parents to children

#### Genetic Variation

Mutations - Accidental change in DNA, can range from the addition, deletion, or substitution of single nucleotide

• Mutation can be passed onto the next generation
• Sexual reproduction can also generate variation

#### Directional selection

• Selection that drives a feature in one direction rather than another

#### Stabilizing selection

• Produces intermediate traits

#### Disruptive selection

• Traits diverge in two or more directions

#### Divergent evolution

• Closely related species that live in different environments and thus experience different selective pressures tend to diverge in their traits as the differing pressures drive the evolution of different adaptions

#### Convergent evolution

• Unrelated species may have similar traits as a result of adapting to selective pressures from similar environments

#### Evolution generates biological diversity

Biodiversity - Total variety of all organisms in an area

Species - Particular type of organism

Population - Group of individuals of a particular species that live in the same area

Speciation - Process by which new species are generated

Allopatric Speciation - Emergence of new species as a result of physical separation of population

#### Population can be separated in many ways

Sympatric Speciation - Occur when species form from populations that become reproductively isolated, occupying a new ecological role or niche within the same geographic area

#### Extinction

• Disappearance of a species from earth

#### Mass extinction

• Massive number of species being killed all at once
• Have been five mass extinctions

#### Levels of ecological organization

Atoms and molecules represent the lowest levels in the hierarchy

Cells - Basic functional units of life

Population - Group of individuals of a particular species that live in the same area

Population Ecology - Quantitative dynamics of how individuals within a species interact with one another

Communities - Multiple interacting species that live in the same area

Community Ecology - Interactions among species

Ecosystems - Encompass communities and the abiotic materials with which their members interact

Ecosystem Ecology - Focus on patterns and nutrient flow by studying living and nonliving components of systems in conjunction

#### Habitat

• Specific environment in which an organism lives in
• A specific habitat consists of both living and nonliving elements
• Habitats vary with the body size and needs for species
• Motile organisms: Organisms that are able to move our freely
• Habitat selection: Motile organisms actively select habitats from among the range of options they encounter
• Sessile animals: Those that are not freely mobile

#### Niche and specialization are key concepts in ecology

• Niche: Reflects its use of resources and its functional role in a community
• Specialists: Species with narrow breadth, and thus very specific requirements
• Generalists: Those with broad tolerances, able to use a wide array of habitats or resources

#### Population show characteristics that help predict their dynamics

• Population size: Expressed as the number of individual organisms present at a given time, may increase, decrease, undergo cyclical change or remain the same over time
• Population density: Describes the number of individuals in a population per unit of area
• Population distribution: Describes the spatial arrangement of organisms within an area. They are 3 types: random, uniform or clumped
• Random distribution: Individuals are located haphazardly in space in no particular pattern
• Uniform distribution: Individuals are evenly spaced
• Clumped distribution: Pattern most common in nature, organisms arrange themselves according to the availability of the resources they need to survive
• Sex Ratio - Proportion of males to females
• Age structure: Describes the relative numbers of individuals of each age within a population
• Birth and death rates: Measure the number of births and deaths per 1000 individuals for a given period of time

#### Survivorship curves

• Type 1: Higher death rates at older ages
• Type 2: Equal rates of deaths at all ages
• Type 3: Higher death rates at younger ages

#### Population may grow, shrink, or remain stable

• Natural rate of population growth: Crude birth rate-crude death rate
• Population growth rate: (crude birth rate-crude death rate) + ( Immigration rate-emigration rate)

#### Limiting factors restrain population growth

Limiting Factors - Physical, chemical and biological characteristics of the environment that restrain population growth

Carrying Capacity - The maximum population size of a species that a given environment can sustain

Density-Dependent Factors - Density of a population can increase or decrease the impact of certain factors on that population.

• Example ﻿$\rightarrow$﻿ Disease, predation

Density-Independent Factor - Influence is not affected by population density ex. Temperature extremes and catastrophic events

#### Reproductive strategies vary from species to species

K-Selected Species -Populations tend to stabilize over time at or near their carrying capacity, because their population stay close to carrying capacity , natural selection in these species favours individuals that invest in producing offspring of high quality that can be good competitors

R-Selected Species - Have high biotic potential and devote their energy and resources to producing as many offspring as possible in a relatively short time