Ecology: Organism-Environment Interactions and Human Impact

Organism-Environment Interactions

Living organisms both affect and are affected by their environment.
Changes in the environment can alter the species present and their population sizes.

Humans are the largest drivers of change in ecosystems and the biosphere.
Deforestation, such as rainforest deforestation, leads to farming but is short-sighted.
Tropical rainforest soils are poor because nutrients are tied up in living organisms.
Deforestation yields a few good growing seasons, after which land is abandoned for more deforestation.
This leads to continuous cutting down of forests for farming or grazing land.

Humans can change their environment, reducing selective pressures.
Human evolutionary changes are now more related to sexual selection and cultural definitions of beauty.

The global human population is around 8,000,000,000.
More people require more food, housing, and clothing, leading to habitat clearing.
Human activity expands into surrounding environments, removing native habitats.
Examples include removing estuaries for farmland, rainforests for farmland, and paving wetlands for housing.

Biodiversity, or biological diversity, measures the health of an ecosystem.
Habitat loss reduces biodiversity.
Biodiversity can be assessed through:
- Genetic diversity: diversity within members of a population.
- Species diversity: number of species and their distribution in an area.
- Ecosystem diversity: diversity within ecosystems and throughout the biosphere.

Decreasing population numbers typically reduce genetic diversity.
Loss of individuals leads to loss of genetic diversity, potentially making species vulnerable.
Genetic diversity can be compared between populations affected by human activities and those less affected.
Loss of diversity affects a species' ability to adapt to negative impacts like disease and famine.
If all individuals have the same genotype due to lost genetic diversity, a condition will affect the entire population.

Includes richness (number of species in an area) and evenness (how evenly distributed they are).
Habitat loss diminishes both factors.
Habitat fragmentation is caused by human activity.

Encompasses diversity within an ecosystem, dispersion of an ecosystem across the globe, and number of different ecosystems in the biosphere.
All these factors diminish with habitat loss.

Conservation biology aims to conserve species by identifying factors limiting species and mediating changes.

Endangered species are in danger of extinction, either globally or in a significant portion of their range.
Threatened species are likely to become endangered in the foreseeable future.
Human activity has accelerated the rate of extinction, potentially leading to another global extinction event.
Extinctions can be local or global.

Provides the basis for many prescription drugs derived from plant or animal products.
Plays roles in ecosystems, such as keystone species.

Increase the number of different species in an area by limiting a particular species.
Ochre stars feeding on California mussels open up space for other organisms.
Beavers dam up streams, creating wetland communities.

Four major ways humans threaten biodiversity:
- Habitat loss
- Invasive species
- Over harvesting
- Global change (e.g., climate change)

Alteration of natural habitat by human activity, driven by increasing population and expansion.
Without protections, habitats are transformed for alternate human functions.

Island biogeography studies how the diversity of organisms on islands differs from the mainland.
Smaller habitat fragments have less diversity.
Habitat fragmentation occurs as human activity engulfs native habitats, creating separated fragments.
Species drop out predictably as fragment size diminishes.
Larger protected habitats are better for diversity than many small ones.
Human activity around fragments causes contact between wild animals and humans, often detrimental to the animals.

Species introduced to an area they did not evolve in, primarily through human activity.
Examples include rats traveling on ships and snakes on airplane landing gear.
Introduction can be deliberate (bringing animals, crops, ornamental plants) or unintentional.
Human activity changing native habitat can expand species ranges.
Non-native species lack native predators or pathogens, allowing them to spread rapidly.
Invasive species can outcompete and displace native species, causing economic loss and collapse of native species.

Disturbed Areas: Open niches which non-native species can get a foothold
High Dispersal: Ability to produce lots of seeds that disperse very readily
Rapid Reproduction: Ability to produce lots and lots of seeds every year
Nitrogen Fixers: Organisms that use legumes tend to their own nitrogen and help out compete lots of other types of species.

Himalayan blackberry: Introduced from Eurasia, forms dense thickets, displaces native species.
Scotts Broom: Introduced from Europe. Displaces natural habitat, seeds are toxic and stay for long periods of time.

Class A: Not established and not threatening, but monitoring is needed.
Class B: Widely established but not totally established, prevention of spread is needed.
Class C: Highly established, removal needs huge efforts.