Adaptation, Biodiversity and

Population Ecology

Chapter 5

QUESTION: ReviewWhich group contains the most species on Earth?

a. Mushrooms

b. Orchids

c. Spiders

d. Beetles

e. Oak trees

QUESTION: ReviewWhich of these pairs of terms is included as causes of biodiversity loss?

a. Pollution and Indicator species

b. Harvesting and Population decline

c. Habitat alteration and Invasive species

d. Overexploitation and Pollination

e. Indicator species and Population growth

QUESTION: Review

Which is NOT a benefit to humans of biodiversity?

a. Economic benefits through ecotourism

b. New potential sources of food

c. New potential sources of drugs

d. Ecosystem services

e. All of the above are benefits of biodiversity.

QUESTION: ReviewWhich has NOT been an approach of conservation biologists?

a. Identifying and mapping areas with large numbers of endemic species.

b. Applying island biogeography theory to habitat fragments.

c. Breeding animals in captivity.

d. Requiring landowners to give up their land.

e. Working with local communities to get them invested in conservation.

QUESTION: Weighing the Issues

When North American pharmaceutical companies go “bioprospecting” in developing countries for compounds for new drugs and medicines, should they be required to pay the host country for its biodiversity?

a. Yes; the biodiversity is a natural resource of the host country, and it should be paid a fee up front.

b. Yes; the biodiversity is a natural resource of the host country, and it should share in any eventual profits from any medicines developed.

c. No; the company is the one doing all the work, so all profits should go to the company.

QUESTION: Interpreting Graphs and DataArachnid species comprise what percentage of ALL species?

a.5.7%

b. 75%

c. 4.3%

d. It cannot be calculated from the information given.

QUESTION: Interpreting Graphs and Data

Extinction rates are…?a. Greater than immigration

rates on small islands

b. Greater on large islands than small islands

c. Greater when number of species are smaller

d. Greater on small islands than large islands

QUESTION: ViewpointsAre parks and protected areas the best strategy for protecting biodiversity?

a. Yes; it is absolutely necessary to preserve untrammeled habitat for species to persist.

b. No; parks won’t matter because climate change will force the biota out of them.

c. No; it is more effective to work with local people and give them economic incentives to conserve nature.

d. Both parks and other strategies are necessary.

QUESTION: Review

Which is a K-selected species?

a. A dragonfly that lays 300 eggs and flies away

b. An oak tree that drops its acorns each year

c. A bamboo plant that flowers only once every 20 years

d. A human who raises three children

e. A fish on the second trophic level

QUESTION: Review

What is the average time for a species on Earth?

a. 1000 years

b. 5000 years

c. 1 million years

d. ~1-10 million years

Question: Review

Which of the following attributes does NOT help predict population dynamics (changes in population):

a. Population sizeb. Population distributionc. Age structured. Sex ratio

QUESTION: Weighing the Issues

Can we continue raising the Earth’s carrying capacity for humans by developing technology and using resources more efficiently?

a. Yes, our growth can continue indefinitely.

b. Our growth can continue some more, but will eventually be halted by limiting factors.

c. No, we cannot raise Earth’s carrying capacity for ourselves any longer.

QUESTION: Weighing the Issues

Are national parks and preserves the best way to conserve biodiversity?

a. Yes, because species depend on their habitats and intact communities being protected.

b. No, because climate change can ruin conservation efforts if it changes conditions inside preserves.

c. Ecotourism and encouraging local interest in conservation is more important than establishing parks.

QUESTION: Interpreting Graphs and Data

You would expect this population to be…?

a. Growing rapidly

b. Shrinking rapidly

c. Stable in size

d. Oscillating in size

QUESTION: Interpreting Graphs and Data

How can you tell that this population growth curve shows exponential growth?

a. Population is increasing.

b. Data points match curve closely.

c. Population is rising by the same number during each interval.

d. Population is rising by the same percentage during each interval.

QUESTION: Interpreting Graphs and Data

This shows growth ending at a(n)

a. exponential… carrying capacity

b. intrinsic… equilibrium

c. logistic… carrying capacity

d. runaway… equilibrium

e. logistic… extinction

QUESTION: Viewpoints

a. Preserves do little good if species can become extinct inside them.

b. Climate change means that we will need more than preserves to save all species.

c. Ecotourism and local participation can make for successful conservation.

What is the most important lesson we can learn from the Monteverde preserve?

Evolution and natural selection

Evolution = genetic change across generations

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

This alters the genetic makeup of populations over time.

Natural selection shapes diversity

Charles Darwin and Alfred Russell Wallace each proposed natural selection as a mechanism for evolution and a way to explain the variety of living things.

A trait that promotes success in natural selection is called an adaptive trait or an adaptation.

A trait that reduces success is maladaptive.

A trait that is adaptive in one location or season may prove maladaptive in another.

Natural selection and genetic variation

For a trait to be heritable, genes in an organism’s DNA must code for the trait.

Mutations are accidental changes in DNA.

Mutations that are not lethal provide the genetic variation on which natural selections act.

In these ways, variable genes and variable environments interact in adapting to environmental conditions.

Biodiversity• Biodiversity, or biological diversity, is the sum of an

area’s organisms, considering the diversity of species, their genes, their populations, and their communities.

• A species is a particular type of organism; a population or group of populations whose members share certain characteristics and can freely breed with one another and produce fertile offspring.

• A population is a group of individuals of a particular species that live in the same area.

Biodiversity

Costa Rica’s Monteverde cloud forest is home to many species and possesses great biodiversity.

Speciation Speciation: The process by which new species come

into being

It is an evolutionary process that has given Earth its current species richness—more than 1.5 million described species and likely many million more not yet described by science.

Allopatric speciation is considered the dominant mode of speciation, and sympatric speciation also occurs.

Allopatric speciation

1. Single interbreeding population

2. Population divided by a barrier; subpopulations isolated

Allopatric speciation3. The two populations

evolve independently, diverge in their traits.

4. Populations reunited when barrier removed, but are now different enough that they don’t interbreed.

Allopatric speciationMany geological and climatic events can serve as barriers separating populations and causing speciation.

Phylogenetic trees Life’s diversification results from countless

speciation events over vast spans of time.

Evolutionary history of divergence is shown with diagrams called phylogenetic trees.

Similar to family genealogies, these show relationships among organisms.

Phylogenetic treesThese trees are constructed by analyzing patterns of similarity among present-day organisms.

This tree shows all of life’s major groups.

Phylogenetic trees

Within the group Animals in the previous slide, one can infer a tree of the major animal groups.

Phylogenetic trees

And within the group Vertebrates in the previous slide, one can infer relationships of the major vertebrate groups, and so on…

Extinction Evolution has not

always progressed in a straight-forward manner, or from simple to complex.

The Burgess Shale fauna were complex and bizarre marine animals from 530 million years ago that vanished completely.

Extinction• Extinction is the disappearance of an entire

species from the face of the Earth.

• Average time for a species on Earth is ~1–10 million years.

• Species currently on Earth = the number formed by speciation minus the number removed by extinction

Extinction Some species are more vulnerable to extinction

than others:

• Species in small populations

• Species adapted to a narrowly specialized resource or way of life

Monteverde’s golden toad was apparently such a specialist, and lived in small numbers in a small area. It was endemic to the forest, occurring nowhere else.

Extinction Until 10,000 years ago, North America teemed with

camels, mammoths, giant sloths, lions, horses, saber-toothed cats, and other large mammals.

Many scientists think their extinction was brought on by hunting after human arrival.

Mass extinctionsEarth has seen five mass extinction events: 50%+ of species were wiped out.

From The Science behind the Stories

An asteroid impact doomed the dinosaurs 65 million years ago.

Today we are beginning a sixth mass extinction as humans alter the planet.

Life’s hierarchy of levels

Organismal Population Community Ecosystem Biosphere

Ecology deals with these levels of life:

Ecology Communities are made up of multiple interacting

species that live in the same area. Ecosystems encompass communities and the

nonliving material with which their members interact. Population ecology investigates how individuals

within a species interact with one another. Community ecology studies interactions among

species. Ecosystem ecology reveals patterns by studying

living and nonliving components of systems in conjunction.

Habitat and niche Habitat = the specific environment where an organism

lives (including living and nonliving elements: rocks, soil, plants, etc.)

Habitat selection = the process by which organisms choose habitats among the options encountered

Niche = an organism’s functional role in a community (feeding, flow of energy and matter, interactions with other organisms, etc.)

Specialists = organisms with narrow breadth and thus very specific requirements

Population ecology Population = a group of individuals of a

species that live in a particular area

Several attributes help predict population dynamics (changes in population):

• Population size• Population density• Population distribution• Sex ratio• Age structure• Birth and death rates

Population sizeNumber of individuals present at a given time

The passenger pigeon was once North America’s most numerous bird, but is now extinct.

Population densityNumber of individuals per unit area

In the 19th century, the flocks of passenger pigeons showed high population density.

Population distributionSpatial arrangement of individuals

Age structure Or age distribution =

relative numbers of individuals of each age or age class in a population

Age structure diagrams, or age pyramids, show this information.

Age structure

Pyramid weighted toward young: population growing

Pyramid weighted toward old: population declining

Sex ratio Ratio of males to

females in a population

Even ratios (near 50/50) are most common.

Fewer females causes slower population growth.

Note human sex ratio biased toward females at oldest ages.

Population growthPopulations grow, shrink, or remain stable,

depending on rates of birth, death, immigration,

and emigration.

(crude birth rate + immigration rate) –

(crude death rate + emigration rate)

= growth rate

Survivorship curves

Type I: survival rates are high when organisms are young and decrease sharply when organisms are old.

Type II: survival rates are equivalent regardless of an organism’s age.

Type III: most mortality takes place at young ages, and survival rates are greater at older ages.

Exponential growth Unregulated populations increase by

exponential growth:

Growth by a fixed percentage, rather than a fixed amount.

Similar to growth of money in a savings account

Exponential growth in a growth curve

Population growth curves show change in population size over time.

Scots pine shows exponential growth

Limits on growth Limiting factors restrain exponential population

growth, slowing the growth rate down.

Population growth levels off at a carrying capacity—the maximum population size of a given species an environment can sustain.

Initial exponential growth, slowing, and stabilizing at carrying capacity is shown by a logistic growth curve.

Logistic growth curve

Population growth: Logistic growth

Logistic growth (shown here in yeast from the lab) is only one type of growth curve, however.

Population growth: Oscillations

Some populations fluctuate continually above and below carrying capacity, as with this mite.

Population growth: Dampening oscillations

In some populations, oscillations dampen, as population size settles toward carrying capacity, as with this beetle.

Population growth: CrashesSome populations that rise too fast and deplete resources may then crash, as with reindeer on St. Paul Island.

Density dependence Often, survival or reproduction lessens as

populations become more dense.

Density-dependent factors (disease, predation, etc.) account for the logistic growth curve.

Other factors (e.g., catastrophic weather events) occur regardless of density, and are density-independent factors.

Biotic potential and reproductive strategies

• Species differ in strategies for producing young.

• Species producing lots of young (insects, fish, frogs, plants) have high biotic potential.

• Others, such as mammals and birds, produce few young.

• However, those with few young give them more care, resulting in better survival.

r and K-selected speciesr-selected species

• Many offspring

• Fast growing

• No parental care

K-selected species

• Few offspring

• Slow growing

• Parental care

Terms come from:

r = intrinsic rate of population increase. (Populations can potentially grow fast, have high r.)

K = symbol for carrying capacity. (Populations tend to stabilize near K.)

Conservation of Biodiversity Ecotourism = tourism focused on visiting natural areas. It provides economic incentive to local communities for

conservation of nature

Canopy walkway in Costa Rican rainforest

Conclusion The golden toad and other Monteverde organisms have

helped illuminate the fundamentals of evolution and population ecology.

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

Understanding ecological processes at the population

level is crucial to protecting biodiversity.