Major themes in 100AEvolution - descent with modification adaptations

- co-evolution among unrelated organisms mutualisms

- radiations: when lineages diversify (= become different) from each other and from their ancestors, and fill many different ecological niches

Ecology - alternative stable states - ecosystem engineers: corals, trees - ecosystem services: earthworms, pollinating insects - forces that maintain versus threaten biodiversity - keystone species

Major themes in 100AEvolution - descent with modification adaptations

Natural selection is good at taking a feature and tweaking it to serve a new function

- sometimes, a key adaptation opens up a whole new range of ecological niches (like dry land)

Why do bryophytes, hermit crabs, and frogs still depend on water to complete their life cycle?

What adaptations allowed insects, snails and reptiles to complete the transition to terrestrial life?

Adaptive RadiationsThe fossil record shows that most species don’t change much, over long periods of time

Groups of “living fossils” show no morphological change for hundreds of millions of years

- horseshoe crabs, coelocanth fishes, nautilus

Then there are adaptive radiations, periods of intense change when a group undergoes an explosive diversification into many ecologically different species

- many new types of species appear in a short period of time, all derived from the same common ancestor

Radiations often follow mass extinctions, when the dominant organisms are wiped out new ecological opportunities open up for the lucky survivors, who fill all the empty niches

Mass extinction is when >60% of all living species are wiped out within 1 million years

Results from extreme, sudden, temporary change in the global environment

rapid change in conditions can eliminate whole groups of organisms – not just species, but entire families or classes

Adaptive Radiations

“Big 5” mass extinctionsEach of these events eliminated 20-60% of all families of plants and animals on the planet

- not species, not genera -- whole families wiped out

end-Permian extinction: 90% of all marine species gone

end-Cretaceous extinction, 65 million years ago: bye-bye dinosaurs

Background extinction = natural selection eliminating poorly adapted lineages; this is happening all the time, at a low rate

Adaptive radiationsUntil 65 MYA, dinosaurs filled all available ecological niches

- air - water

- land predators - herbivores

- air - water

- big herbivores- predators

Mackenzie 2003

Seedlessplants

Gymnospermsdominate

Angiosperms dominate

First gymnosperms

# of

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First angiosperms

Note that each major group of plants appeared long before that group became dominant

could not take over until a mass extinction ( ) wiped out the group that was previously dominant

Plant Evolution following Mass Extinctions

The Cambrian Explosion565 million years ago, only sponges + cnidarians, maybe some simple worms were here Just 40 million years later, all animal phyla were present - arthropods, annelids, molluscs...even primitive vertebrates

- some forms so wild, they can’t be classified

All major body plans appeared “overnight,” in geological terms

Since the Cambrian Explosion, no new animal phyla evolved

This diversification in such a short window of time was the most important adaptive radiation in the history of life

Why did so many new body plans evolve in such a short time?

What led to the Cambrian explosion?3 hypotheses for the explosive innovation in body plans:

(1) major groups diversified due to changes in new master control genes that regulated development

(2) higher O2 levels made larger, more complex bodies possible

(3) ecological interactions

a) arms races (between predators and prey) fuelling diversity

b) mass extinction may have wiped out dominant jellyfish allowing other life forms to thrive and diversify

(1) Changes in developmental genes

Network of developmental control genes was in place in the earliest bilaterian animal; present in all modern animals

- govern how complex bodies develop from a fertilized egg

- mutations affecting when these master genes switch on big changes in the body that develops

Flies with a single mutation grow legs where antennae go

leg

fly mutanthead, flynormal head

antenna

5 things to know about ecology1) ecosystems have alternative stable states

2) ecosystem engineers create habitat from their bodies or changes they make to the environment (corals, trees, beavers, deep-sea vent worms)

3) ecosystem services: our profit from natural processes (earthworms, pollinating insects, decomposers)

4) biodiversity = ecosystem stability

- protection from invasive species, fisheries collapse

5) keystone species: lose one species lose 1000s of other, dependant species

1. Alternative stable statesecosystems are often in balance, or equilibrium, meaning they go on without changing for long periods of time

A) however, this doesn’t mean the ecosystem will return to that state following a disturbance

B) same community of species living in same environmental conditions may end up in different “stable states” – meaning, they can reach a very different balance

- may depend on random fluctuations in population sizes

- may reflect different starting conditions (which species was initially more abundant, for example)

Example: Rainforest trees

Common trees produce few seedsRare trees produce many seeds

What happens if you cut down the common trees?

The formerly rare species may now take over, out-competing what used to be the common species

Ecosystem may never return to its previous balance after a disturbance (for example, human-caused de-forestation)

Two nearby African islands have very different communities

- 70% of animals are lobsters

Why are there lobster on one island, and snails on the other? - beds of mussels, algae &

snails cover the rocks

- snails can’t open healthy mussels

Malgas Marcus

Two nearby African islands have very different communities

- 70% of animals are lobsters

- snails are immediately preyed on (eaten) by lobsters

Malgas Marcus

Two nearby African islands have very different communities

Malgas Marcus

- lobsters transplanted to Marcus Island were swarmed by >300 snails, and totally eaten within 15 minutes !

thus, prey become the predators when their starting numbers are high enough

2. Ecosystem engineersecosystem engineers modify their environment, building physical structures that serve as habitat for other organisms

- can be their bodies: corals, trees

2. Ecosystem engineersecosystem engineers modify their environment, building physical structures that serve as habitat for other organisms

- can be their bodies: corals, trees- can be their homes, or products of their activities

termite moundsbeaver dam

these organisms increase biodiversity (understand why)

3. Ecosystem servicesWe are used to paying for human services (economics), but are used to getting free services from our ecosystems

- we typically don’t notice these services until they disappear, due to disruption of an ecosystem by our activities

people need to recognize the economic benefits of intact ecosystems, to be motivated to conserve nature

- estimated that life on earth would end in ~6 months if insects disappeared... why?

example: coastal communities are protected from storm surge by coral reefs and wetlands, both of which are

endangered by development, agriculture, climate change and pollution

3. Ecosystem servicesColony collapse: huge loss of honeybees started in 2006

- lost 30% of bee hives in U.S. but problem is global

- bees are critical pollinators for 1/3rd of human food crops

- source of bee die-off is unclear: combination of pesticides and poor nutrition may make bees vulnerable to viruses,

mites and fungal pathogens

In one region of China, excessive pesticide use in the 80’s wiped out all bees... farmers must now hand-pollinate every flower on every tree and plant to fertilize their crops

4. BiodiversityBiodiversity includes

- the variety of species present- the genetic diversity they encompass

- a major goal of biology is to catalogue biodiversity, and understand how it maintains the health of an ecosystem

organisms interact with each other in complex ways thatmaintain a natural balance, and permit many species toco-exist together

disruption of that balance, by removal of even one species,can have disastrous effects on an ecosystem

Threats to Biodiversity – Invasive species- introduced (accidentally or intentionally) to a new area

- with no native predators, quickly over-run native species, disrupt ecosystem at a cost of $137 BILLION per year in the U.S. alone (Pimentel et al. 2000)

Brown tree snake was accidentally brought to Guam; ate all the birds

“killer algae” Caulerpa taxifolia

took over the Mediterranean

cost $6 million to eliminatefrom San Diego

Threats to Biodiversity – Habitat lossOver half of all species predicted to be gone by end of this century; each plays a role in its ecosystem that will be lost

habitat loss is implicated in 3/4th of extinctions- 7% of earth is currently set aside as nature preserves- a major goal now it to preserve hotspots of biodiversity

Together, 1/3rd of all plants and vertebrates inhabit only 1.5% of the earth (mainly in rain forests and chaparral)

By recognizing its economic value (ecotourism, ecosystem services), local people may be convinced to preserve the biodiversity and health of their ecosystems

Environment & human healthThe link between environmental health and human health is increasing clear, but not appreciated by most voters

Why is cancer risk directly tied to race?

Morello-Frosch & Jesdale, 2006 Environ Health Perspect. 114: 386–393

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Why care about ecology?

The link between environmental health and human health is increasing clear, but not appreciated by most voters

check out Natural Resources Defense Council --

http://www.nrdc.org

check out Environmental Justice link

- learn how minority communities are targeted by corporate polluters and what is being done to combat this injustice