Biodiversity changes over time

How far back does the fossil record of life on Earth extend

• It extends back 3.5 billion years to a time when the most complex organisms were cyanobacteria

  

What patterns are observed in the fossil record

• The fossil record is marked by major pulses of speciation and extinction

Approximately what percentage of all species that have ever lived are now extinct

• Around 99% of the ~4 billion species that have evolved are extinct

What is background extinction

• It is the continuous, low level of species extinction that has occurred throughout most of Earth's history

What determines Earth's biodiversity over time

• The balance between the formation of new species and the extinction of existing ones

What is a mass extinction

• A mass extinction is the extinction of many species in a relatively short geologic time period

How many mass extinctions has Earth experienced, and what percentage of species went extinct in them

• Earth has experienced five mass extinctions, during which 50–95% of species went extinct

How has human activity affected biodiversity in modern times

• Human encroachment has caused many species extinctions, reducing biodiversity and pushing Earth toward a sixth mass extinction

What are the ecological consequences of mass extinctions

• They leave behind empty niches, which surviving or new species can exploit

What happens to species that exploit empty niches after a mass extinction

• Natural selection acts on them, leading to better adaptation and often speciation

How do lineages evolve after mass extinctions

• Isolated populations adapt to different niches, leading to diversification and adaptive radiation

What is an example of adaptive radiation after a mass extinction

• After the extinction of the dinosaurs 65 million years ago, mammals diversified into many new niches

Which groups have the best fossil records for studying speciation

• Marine bivalves, gastropods, plankton, and bryozoans have better fossil records than mammals or plants

What does the fossil record help us understand about speciation

• It helps identify periods of rapid species diversification, especially after mass extinctions

What surprising discovery was made in 1980 about insects in tropical forests

• In one study of 19 trees in Panama, 80% of the 1,200 beetle species discovered were new to science

What comparison highlights our limited knowledge of biodiversity

• Scientists know more about the number of stars in the galaxy than the number of species on Earth

How fast are species becoming extinct compared to the background extinction rate

• Currently 100 to 1,000 times faster, and potentially 10,000 times faster by the end of the century

  

According to the 2005 Millennium Ecosystem Assessment, what proportion of Earth's land surface has been disturbed by humans

• At least half, possibly up to 83% (excluding Antarctica and Greenland)

What is local extinction

• When a species disappears from a specific area but exists elsewhere

What is ecological extinction

• When a species exists in such low numbers it no longer plays its ecological role

What is biological extinction

• When a species is no longer found anywhere on Earth—extinction is permanent

How many species are officially listed as at risk of extinction

• Around 30,000, though the actual number is likely much higher

Why are fish the most threatened group of species

• Due to overfishing, habitat degradation, and pollution

Why should we prevent premature extinction of species

• Because of their ecological and economic services and their intrinsic right to exist

Name five human activities causing species extinction

• Unsustainable hunting/harvesting

• Habitat destruction (e.g., deforestation, urban sprawl)

• Introduction of diseases, parasites, predators

• Pollution (air, water, soil)

• Climate change

How can short-term events like volcanoes or fires threaten biodiversity

• They can devastate species with limited ranges, especially endemic species

How did fire affect the Leadbeater’s Possum

• Fire worsened the species’ stress from habitat loss and reduced nesting sites

What are the effects of El Niño and La Niña on marine species

• They can alter ocean temperatures, shifting the ranges of marine species

How has climate change affected fish distributions in Tasmania

• Fish not previously recorded in Tasmania have now been found due to warming waters

How does continental drift affect biodiversity

• It creates isolated environments that can lead to speciation over time

Why do tropical ecosystems have higher biodiversity

• Stable, warm, and productive environmental conditions near the equator support more species

Why does Australia have so many endemic species

• Due to its long-term geographic isolation after separating from Gondwana ~40 million years ago

What percent of Australia's vascular plants are endemic

• 92%

What percent of Australian mammals are endemic

• 83%

What are the endemism rates for birds, reptiles, and frogs in Australia

• Birds: 45%

• Reptiles: 89%

• Frogs: 93%

What’s Australia’s record for species extinctions since European settlement

• 126 species extinct (83 plants, 43 animals including 19 mammals, 21 birds, 3 frogs)

What is a biodiversity hotspot

• A biogeographic region with high levels of biodiversity that is under threat from humans

What is the fossil record

• A collection of fossils showing extinct life and changes in life forms over time

What does the fossil record support

• The theory of evolution, showing consistent appearance of organisms in a specific order

According to fossil evidence, what types of organisms appeared first

• Prokaryotes before eukaryotes

• Single-celled before multicellular

• Invertebrates before vertebrates

• Amphibians before dinosaurs

• Ferns before flowering plants

Why are soft-bodied organisms rarely fossilized

• Because they decay quickly and lack hard parts like bones or shells

How is the geological timescale organized

• Into eons → eras → periods

What marks the boundaries between geological time intervals

• Abrupt changes in fossil characteristics, such as mass extinctions or new species

What is the principle of superposition

• In undisturbed strata, the oldest layers are at the bottom and the youngest at the top

What is stratigraphy

• Estimating the relative age of rock layers based on their position and index fossils

Why don’t igneous rocks contain fossils

• Because they form from hot lava, which would destroy organic material

What kind of rock typically contains fossils

• Sedimentary rock, formed by compression of mud, silt, or sand

What are index fossils

• Fossils of species that lived for a short, known time and are used to date rock layers

How does radiometric dating work

• By measuring the decay of radioactive isotopes in igneous rock

Why can't radiometric dating be used on sedimentary rocks directly

• Because the minerals in sedimentary rocks formed before the rock itself did

What is an isotope

• An atom of an element with a different number of neutrons

What is a radioactive isotope

• An unstable atom that decays into a stable product (e.g. Carbon-14 → Nitrogen)

What is relative dating in geology

• A method of determining the order of past events by comparing rock layers (strata), without determining their exact age. It uses principles like the law of superposition and index fossils

What is numerical (absolute) dating in geology

• A method of determining the exact age of rocks or fossils in years using radiometric dating, based on the decay of radioactive isotopes in igneous rocks

What happens in the first stage of allopatric speciation

• The parent population expands into new areas (due to factors like competition).

• All individuals still share a common gene pool with regular gene flow.

How does allopatric speciation progress after expansion

• Stage 2: Geographical isolation (e.g., by continental drift or sea level change) prevents gene flow.

• Stage 3: Different environments lead to different selection pressures; populations become subspecies.

• Stage 4: Reproductive isolation occurs; even if barriers are removed, genetic isolation is complete, and new species have formed.

What is sympatric speciation and how is it different from allopatric speciation

• It's the formation of a new species within the same geographic area as the parent species. No physical separation occurs.

• It's rarer in animals, but common in plants, often due to polyploidy, habitat preference, or food source changes.

What are the stages of sympatric speciation

• Stage 1: A change in habitat or food preference (e.g., insect lays eggs on a new plant).

• Stage 2: Reproductive isolation forms as the new group mates and raises offspring only within their new habitat.
  Over time, these groups diverge into distinct species.

What does the global distribution of species suggest about their evolution

It suggests that modern species evolved from ancestral populations that radiated out into new environments.

Examples of this are seen on islands where isolation led to diversification:

• Galapagos Islands

• Cape Verde Islands

• Tristan da Cunha