Chapter 3- Evolution, Biodiversity, and Population Ecology

Chapter 3- Evolution, Biodiversity, and Population Ecology

Chapter 3- Evolution, Biodiversity, and Population Ecology

This lecture will help you understand:

Natural selection

How evolution influences biodiversity

Reasons for species extinction

Ecological organization

Population characteristics

Population ecology

Conserving biodiversity

Central Case Study: Saving Hawaii’s Native Forest Birds

Evolution in the Hawaiian Islands has generated hundreds of species, many unique to the islands

The island chain was once home to 140 species of native birds

In recent times, half of the native bird species have gone extinct

a)Introduced species (like pigs, cattle, rats, and cats) destroyed habitat and killed eggs and young

b)Avian malaria killed native birds at lower elevations

Evolution: The Source of Earth’s Biodiversity

Species = a population or group of populations whose members share characteristics

a)They can breed with one another and produce fertile offspring

Population = a group of individuals of a species that live in the same area

Evolution = change over time

a)Biological evolution = change in populations of organisms over generations

b)Genetic changes lead to changes in appearance, functioning, or behavior

Evolution: The Source of Earth’s Biodiversity

Genetic changes in evolution may be random

a)But may be directed by natural selection

Natural selection = process in which traits that enhance survival and reproduction are passed on more frequently to future generations than those that do not

a)Genetic makeup of future populations is changed

Evolution: The Source of Earth’s Biodiversity

Evolution is one of the best-supported and most illuminating concepts in all science

a)It is the foundation of modern biology

We must understand it to appreciate environmental science

a)Understanding how species change over time and adapt to their surroundings is crucial for comprehending ecology and the history of life

b)Evolutionary processes influence pesticide resistance, agriculture, medicine, health, etc.

Natural selection shapes organisms and diversity

In 1858, both Darwin and Wallace proposed natural selection as the mechanism of evolution

Premises of natural selection:

a)Organisms struggle to survive and reproduce

b)Organisms produce more offspring than can survive

c)Individuals of a species vary in their characteristics due to genes and the environment

d)Some individuals are better suited to their environment and reproduce more effectively

Organisms with better adapted traits will produce more offspring

Natural selection shapes organisms and diversity

Adaptation = the process where, over time, characteristics (traits) that lead to better reproductive success become more prevalent in the population

Adaptive trait (adaptation) = a trait that promotes reproductive success

Mutations = accidental changes in DNA that may be passed on to the next generation

a)Non-lethal mutations provide the genetic variation on which natural selection acts

Sexual reproduction also leads to variation

Directional selection = drives a feature in one direction

Selective pressures from the environment influence adaptation

Related species in different environments experience different pressures and evolve different traits

Convergent evolution = unrelated species may acquire similar traits because they live in similar environments

Evidence of natural selection is all around us

It is evident in every adaptation of every organism

Artificial selection = the process of selection conducted under human direction

a)Produced the great variety of dog breeds and food crops

Evolution generates biodiversity

Biological diversity (biodiversity) = the variety of life across all levels of biological organization





Scientists have described 1.8 million species

a)Estimates of the total number of species that exist range from 3 million to 100 million

b)Biodiversity exists nearly everywhere

Speciation produces new types of organisms

The process of generating new species from a single species

Allopatric speciation = species formation due to physical separation of populations

a)The main mode of speciation

b)Populations can be separated by glaciers, rivers, mountains

c)Each population gets its own set of mutations

d)Natural selection can speed the process

We can infer the history of life’s diversification by comparing organisms

How did the major groups of organisms come to be?

Phylogenetic trees = diagrams that show relationships among species, groups, genes, etc.

a)Scientists can trace how certain traits evolved

b)Some traits evolved and were passed on

c)Other traits evolved more than once (e.g., the ability to fly)

We can infer the history of life’s diversification by comparing organisms

Knowing how organisms are related to one another helps scientists organize and name them

Categories reflect evolutionary relationships

a)Scientists use physical and genetic characteristics to organize

Each species gets a two-part Latinized scientific name

The fossil record teaches us about life’s long history

Fossil = an imprint in stone of a dead organism

Fossil record = the cumulative body of fossils worldwide

The fossil record shows:

a)Life has existed on Earth for at least 3.5 billion years

b)Earlier types of organisms evolved into later ones

c)The number of species has increased over time

d)Most species have gone extinct

e)There have been several mass extinctions in the past

Speciation and extinction together determine Earth’s biodiversity

Extinction = the disappearance of a species from Earth

a)Species last 1–10 million years

Extinction has historically been a natural occurrence

a)The loss of a species is irreversible

Speciation and extinction together determine Earth’s biodiversity

Human activity profoundly affects rates of extinction

Biodiversity loss affects people directly

a)Food, fiber, medicine, ecosystem services

Some species are especially vulnerable to extinction

Extinction can occur when the environment changes rapidly and natural selection can not keep up

Many factors cause extinction:

a)Severe weather, climate change, changing sea levels

b)Arrival of new species

c)Being a small population or specialized species

Some species are especially vulnerable to extinction

Endemic species = a species that only exists in a certain, specialized area

a)Very susceptible to extinction

b)Usually have small populations

c)Island species are often endemic and thus at risk

Some species are especially vulnerable to extinction

Many U.S. amphibians have very small ranges

a)They are vulnerable to extinction

b)For example, the Yosemite toad, Houston toad, Florida bog frog

Forty salamander species are restricted to areas the size of a typical county

Earth has seen several episodes of mass extinctions

Background extinction rate = a constant, slow rate of extinction that occurs as a part of evolution

Mass extinction events = episodes that killed off massive numbers of species at once

a)Occurred five times in Earth’s history

b)50–95% of all species go extinct at one time

Cretaceous–Tertiary (K–T) event: 65 million years ago

a)Dinosaurs went extinct

End-Permian event: 250 million years ago

a)75–95% of all species went extinct

The sixth mass extinction is upon us

Humans are causing the sixth mass extinction event

a)Resource depletion, population growth, development

b)Destruction of natural habitats

c)Hunting and harvesting of species

d)Introduction of non-native species

Today’s extinction rate is 100–1000 times higher than the background rate and rising

It will take millions of years for life to recover

We study ecology at several levels

Ecology and evolution are tightly intertwined

Biosphere = the total of living things on Earth and the areas they inhabit

Community = interacting species that live in the same area

Ecosystem = communities and the nonliving material and forces they interact with

We study ecology at several levels

Population ecology = investigates the dynamics of population change

a)The factors affecting the distribution and abundance of members of a population

b)Why some populations increase and others decrease

Community ecology = focuses on patterns of species diversity and interactions

Ecosystem ecology = studies living and nonliving components of systems to reveal patterns

a)Nutrient and energy flows

Each organism has habitat needs

Habitat = the environment where an organism lives

a)It includes living and nonliving elements

Habitat use = each organism thrives in certain habitats, but not in others

a)Results in nonrandom patterns of use

Habitat selection = the process by which organisms actively select habitats in which to live

a)Availability and quality of habitat are crucial to an organism’s well-being

b)Human developments conflict with this process

Each organism has habitat needs

Habitats vary with the body size and needs of species

a)A soil mite vs. an elephant

Species have different habitat needs at different times

a)Migratory birds use different habitats during migration, summer, and winter

Species use different criteria to select habitat

a)Soil, topography, vegetation, other species

b)Water temperature, salinity, prey

Species survival depends on having suitable habitat

Niche and specialization are key concepts in ecology

Niche = summary of everything an organism does

a)Use of resources

b)Functional role in a community: habitat use, food selection, role in energy and nutrient flow, interactions with other individuals

Niche and specialization are key concepts in ecology

Specialists = species that have narrow niches and specific needs

a)Extremely good at what they do

b)But vulnerable when conditions change

Generalists = species with broad niches

a)Use a wide array of habitats and resources

b)Can live in many different places

Population Ecology

Population = individuals of a particular species that inhabit an area

Species may have different arrangements of their populations

a)Some populations (like the nēnē) exist as isolated populations

b)Others (like humans) exist as
large continuous populations

Populations show characteristics that help predict their dynamics

Certain characteristics of a population help scientists predict what will happen to them in the future

a)Helps in managing threatened species

Population size = number of individuals present at a given time

a)Populations generally grow when resources are abundant and predators are few

b)Decline in response to loss of resources, other species, disasters

Population density

Population density = the number of individuals in a population per unit area

High densities have advantages and disadvantages

a)Easier to find mates

b)Increased competition and vulnerability to predation

c)Increased transmission of diseases

d)Sometimes causes organisms to leave an area if too dense

Low densities provide access to plentiful resources and space but make it harder to find mates

Population distribution

Population distribution (dispersion) = spatial arrangement of organisms

Random = haphazardly located individuals, with no pattern

Uniform = individuals are evenly spaced

a)Territoriality, competition

Clumped = organisms found close to other members of population

a)Most common in nature

b)Clustering around resources

c)Mutual defense

Sex ratio and age structure

Sex ratio = proportion of males to females

a)In monogamous species, a 1:1 sex ratio maximizes population growth

b)Most species are not monogamous, so ratios vary

Age distribution (structure) = the relative numbers of organisms of each age in a population

a)Age structure diagrams (pyramids) show the age structure of populations

In species that continue growing as they age, older individuals reproduce more (e.g., a tree)

a)Experience can help older individuals breed more

Birth and death rates

Survivorship curves = graphs that show that the likelihood of death varies with age

a)Type I: higher death rate at older ages

a)Larger animals (e.g., humans)

b)Type II: same death rate at all ages

a)Medium-sized animals (e.g., birds)

c)Type III: higher death rate at young ages

a)Small animals, plants

Populations may grow, shrink, or remain stable

Natality= births within the population

Mortality= deaths within the population

Immigration= arrival of individuals from outside the population

Emigration= departure of individuals from the population

Births and immigration add individuals; deaths and emigration remove individuals

Crude birth (death) rates = number of births (deaths) per 1000 individuals per year

Populations may grow, shrink, or remain stable

Natural rate of population increase=

(Crude birth rate)  (crude death rate)

a)Population change due to internal factors

Population growth rate=

(Crude birth rate  immigration rate)  (Crude death rate  emigration rate)

a)Net changes in a population’s size/1000/year

Growth rate as a percent = Population growth
rate  100%

a)Populations of different sizes can be compared

Unregulated populations increase by exponential growth

Exponential growth = whena population increases by a fixed percent

a)Graphed as a J-shaped curve

Exponential growth cannot be sustained indefinitely

It occurs in nature with:

a)Small population

b)Low competition

c)Ideal conditions

Occurs often with introduced species

Limiting factors restrain population growth

Limiting factors= physical, chemical, and biological attributes of the environment that restrain population growth

a)Space, food, water, mates, shelter, suitable breeding sites, temperature, disease, predators

Carrying capacity= the maximum population size of a species that its environment can sustain

Limiting factors slow and stop exponential growth

a)An S-shaped logisticgrowth curve

The influence of some factors depends on population density

Density-dependent factors= limiting factors whose influence is affected by population density

a)Increased density increases the risk of predation, disease, and competition

b)Results in the logistic growth curve

c)Larger populations have stronger effects of limiting factors

Density-independent factors= limiting factors whose influence is not affected by population density

a)Events such as floods, fires, and landslides

The logistic growth curve is a simplified model

Few populations in nature match the curve exactly

Carrying capacities can change

Environments are complex and ever-changing

a)Limiting factors can change, altering the carrying capacity

Humans lower environmental resistance for themselves

a)Increases our carrying capacity

b)Technologies overcome limiting factors

In increasing carrying capacity for humans, we now use immense portions of the planet’s resources

a)We have reduced the carrying capacity for countless other organisms

Reproductive strategies vary among species

Biotic potential= an organism’s capacity to produce offspring

K-selected species= species with long gestation periods, few offspring, and strong parental care

a)Have a low biotic potential

b)Stabilize at or near carrying capacity; good competitors

r-selected species= species that reproduce quickly and offer little or no care for offspring

a)Have a high biotic potential

b)Populations fluctuate greatly

Conserving Biodiversity

Humans are developing land, extracting resources, and growing as a population

a)This increases the rate of environmental change for other species

Science can help us understand how we are changing the environment

Impacts threatening biodiversity have complex social, economic, and political roots

a)We must understand these factors to solve problems

Introduced species pose challenges for native populations and communities

Some introduced species thrive in their new environments, eliminating native species

Native island species are particularly vulnerable

a)Evolved in isolation with limited need for defenses

Biologists and land managers often must eradicate introduced species to protect native habitats

a)In Hawaii, pigs are being hunted and pig-free areas are being fenced off

Innovative solutions are working

Scientists, land managers, and private citizens are protecting the native species and habitats of Hawaii

a)Invasive species are being removed

b)Native species (like the nēnē) are being protected, and new populations are being started

c)Ranch land is being restored to forest

d)Coral reef communities are part of the largest federally protected marine reserve in the world

This restored and protected land has resulted in ecotourism = the phenomenon of people visiting the islands to experience the natural areas

Climate change now poses an extra challenge

Climate change is altering how we protect species and habitats

Land is typically protected to conserve the species that live there

a)As the climate changes, the protected land may no longer support the same species


The fundamentals of evolution and population ecology are integral to environmental science

Natural selection, speciation, and extinction help determine Earth’s biodiversity

Understanding how ecological processes function
at the population level is crucial to protecting biodiversity