Biodiversity & Evolution, part 2

Miller & Spoolman, 16th ed

Big Idea #4

◊ Human activities decrease biodiversity

What is a “species”?

◊ A species is a group of the same type of organism that can breed with each other and produce fertile offspring.

How do we get new species?

◊ Speciation - the formation of new species

◊ Most common mode of speciation:◊ Geographic isolation - members of a

population physically separated (due to migration, mountain range, road) - over time they may become separate species

◊ Geographic isolation may lead to reproductive isolation - the two groups can no longer reproduce or produce fertile offspring

◊ When groups are reproductively isolated, they are different species

◊ Geographic isolation may lead to reproductive isolation - the two groups can no longer reproduce or produce fertile offspring

◊ When groups are reproductively isolated, they are different species

Reproductive isolation ◊ Takes a long time

• In fastest breeding organisms - 10s - 100s of years

• In slower breeding organisms - 1000s to millions of year

Gestation 660-760 days, 5 years between births Gestation 12-13 days,

births every year

Extinction is Forever :’(

◊ Extinction - an entire species ceases to exist

http://aso.gov.au/titles/historical/tasmanian-tiger-footage/clip1/

Who is vulnerable to extinction?◊ Endemic species - found in only one place◊ Resource specialist species - eat a limited

food range or live in only one type of habitat

Types of extinction

◊ Background extinction - low rate of species extinction that occurs all the time - on average 1-5 species/million/year

Does it really matter?

◊ Mass extinction = significant rise in extinction rate where large groups of species are wiped out

◊ ~ 250 mya about 95% of all species went extinct (dinosaurs)

Extinction and biodiversity

◊ When species go extinct, it opens new habitat and resources for other species - possibly leading to the formation of new species

Quick Think◊ How would you respond to someone

that says that because extinction is a natural process, we should not worry when a species becomes endangered due to human activities?

Big Idea #5

◊ Biodiversity increases the sustainability to ecosystems

How do we measure species diversity? ◊ 2 major components:

• Species richness - the number of different types of species

• Species evenness (aka species number) - the relative abundance of each species

Simple example

◊ High School A has 1000 students• 350 white students• 400 black students• 250 Hispanic

students

◊ High School B has 1000 students• 950 white students• 20 black students• 30 Hispanic students

More “real” example

◊ Tropical rain forest• 10,000s of different

species, but low numbers of each type

◊ Deciduous forest• Only a few

dozen different species, but high numbers of each one

Where is it most diverse?◊ It varies with the

geographic location◊ On average, there are

more plants and animals near the equator, and the numbers decline as you move toward the poles (plus ocean bottom)

Most diverse

◊ Four MOST species rich environments:• Tropical rain forests• Coral reefs• Ocean bottom• Large tropical lakes

High species richness

◊ Areas that have high species richness also have higher primary productivity and tend to be more stable ecosystems• More plants support more consumers• More consumers and plants means more

connections

Islands

◊ Theory of island biogeography - the number of species on an island is determined by 2 things: immigration rate and extinction rate

2 Things about the island affect these rates:◊ 1. Size of the island

• Smaller islands have less species because it is a smaller target out there for colonizers

◊ So lower immigration rate

◊ Smaller islands also have higher extinction rates• Have fewer resources and less ecosystem

diversity

◊ 2. Distance from the mainland• Closer to the mainland tends to have

higher immigration rate and thus more species

This work is important because◊ We create islands

when we develop land◊ Scientists use this

theory to determine how big the island needs to be to maintain biodiversity

Quick Think◊ If you could design a healthy,

sustainable ecosystem, but you had to choose between high species richness and low evenness, or the opposite, which would you choose and why?

Big Idea #6

◊ Each species plays an important role in its ecosystem

Ecological Niche ◊ The role that a species plays in the

ecosystem• It includes everything that affects its

survival and reproduction• Water, sunlight needs• Space requirements• Temperature tolerance• Food, resource needs

Habitat

◊ Where a species lives◊ (Niche is the WAY it lives)

2 main types of niches

◊ Generalists - broad niche• Can live in many places• Eats a variety of foods• Can tolerate a range of conditions• Examples: mice, deer, raccoons, humans,

flies

◊ Specialists - narrow niche• Only live in one type of habitat• Use one or just a few food types• Tolerate a small range of environmental

conditions• Examples: tiger salamanders, Giant

pandas, flamingos, koalas

Pros and Cons of each type

◊ Generalist -• More competition• More adaptable to

change

◊ Specialist• Little or no

competition• Not adaptable to

change

5 especially important niches

◊ Native species◊ Nonnative species

◊ Keystone species◊ Indicator species◊ Foundation species

(aka ecosystem engineers)

Muskrat - invasive in CA

Native species◊ Species that normally live in a given

area• They have evolved along with the other

native species and have intricate connections with them

Nonnative species

◊ Aka alien, invasive, exotic◊ Accidentally or deliberately introduced

◊ Not always bad - most crops and livestock are nonnative species

◊ Sometimes they ARE bad - in 1957 Brazil introduced wild African bees (aka “killer bees”) to increase honey bees. These bees out-competed native bees and led to a decrease in honey production

More on nonnative species

◊ Sometimes - an introduces species just dies out • The new area is not favorable to it

◊ Sometimes, the nonnative species flourishes, but with no harm to other organisms• Habitat is favorable• Native species peacefully coexist with it

◊ Sometimes - nonnative species takes over• Often there are no predators for this

species, since it hasn’t evolved alongside them

• This gives the nonnative a competitive advantage

Indicator Species

◊ Provide ecologists with an early warning system for damage to the ecosystem

◊ They are the canaries in a coal mine

Examples:◊ Birds - found almost everywhere,

heavily affected by environmental damage, especially chemical pesticides

Examples◊ Amphibians - breathe partially through

skin, so very sensitive to changes in water quality

Keystone species

◊ Have a large effect on the number and type of other species in the ecosystem

Examples:

◊ Top predators - feed on and help regulate the size of of other species

◊ Pollinators - control the size of plant populations

Effects of losing a keystone species◊ When a keystone species is lost - it

leads to population crashes and extinctions of other species

Foundation Species◊ Aka ecosystem engineers◊ Play a major role in creating the

ecosystems in which they live

Examples:◊ Elephants pull out or break small trees

in the African savannah◊ This allows grass to grow and benefits

other grazers and open plains predators

Examples:

◊ Beavers - build dams to create ponds that other species benefit from

Quick Think◊ Should we devote more of our budget

to protecting keystone and foundation species, perhaps at the peril of other species? Explain your reasoning.