Lecture 2: Lecture 2: Human Human ImpactImpact4 Major Activities thatThreaten Biodiversity

– 1)Habitat Destruction– 2)Introduced Species– 3)Overexploitation– 4)Disruption of

Interaction Networks

1: Habitat Destruction 1: Habitat Destruction Includes:Includes:

• 1)Habitat Alterations•Selective Logging•Edge Effects

• 2)Habitat Fragmentation

• 3) Clear Cutting

Effects of Habitat Effects of Habitat Destruction:Destruction:• 1) Selective logging causes gaps in the

canopy thus causing an edge effect.• The edges slowly degrade do to wind, invasion of

species, and increased sunlight. Degradation of edges can lead to habitat fragmentation.

• Some species may become more susceptible to predation because of decreased protection from the forest

• 2) Habitat fragmentation cuts species off from larger populations thus causing inability to support viable populations.

• 3) Clear cutting for agriculture and pastures.• Because Tropical Rainforest soil is low in nutrient

quality approximately 10x more land is needed for grazing animals and the previously cleared ag land is abandoned to clear nearby forest to further grow crops.

• Millions of hectares of Brazilian Amazon Rainforest are destroyed every year due to human set fires for agriculture use and by ranchers.

Habitat Destruction Habitat Destruction Disrupts Chemical Cycles Disrupts Chemical Cycles of Ecosystemsof Ecosystems• Nutrient exhaustion in the tropics due to

clear-cutting effects the Nitrogen Cycle• This causes an increase in the decomposition rate of

organic matter• Slash and Burn practices of forests causes

greater releases of nitrogen oxides which contribute to atmospheric warming.

• Excess nitrogen and runoff contaminate freshwater and marine ecosystems.

• Deforestation leads to a rise in CO2 levels

Land Behavior Affects the Land Behavior Affects the Oceans TooOceans Too

Pictured Below: Damaged Coral

• Runoff of sediments, fertilizers, and pollutants due to changes in the nitrogen cycle, agriculture, and tourism increasing development along the coasts

•Pollutants directly block the light thus killing the corals

•Pollutants also clog polyps on the corals so the corals cannon perform necessary life functions such as gaining food and oxygen

•An increase in nutrients can also lead to an increase growth of algae, which results in the death of corals

Human Activities lead to Rising Human Activities lead to Rising Atmospheric COAtmospheric CO22 • A rise in CO2 causes the greenhouse gas effect where heat is trapped, thus warming the planet.

• Warming of the atmosphere causes a warming of ocean temperatures

• Warming ocean temperatures cause coral bleaching a phenomenon that turns corals white due to the expulsion of zooxanthella (organisms that provide up to 90% of energy to corals) which in turn leads to coral death

• A rise in temp will melt the polar ice caps, rising the current sea level.

What Habitat Destruction What Habitat Destruction and Human Impact Means for and Human Impact Means for the Coral Reefsthe Coral Reefs

Human Impact directly and indirectly effects the coral reefs. It causes the corals inability to recover quickly, a reduction in

growth, and reef mortality.

2: Introduced Species2: Introduced Species

• Above: Zebra Mussel, an invasive species introduced to North America via ballast water

• Invasive or exotic species are species that humans move (intentionally or unintentionally) from the species native habitat to a new geographic region

• Introduced species can disrupt the geographic region they were introduced to causing a disruption of “interaction networks”.

3: Overexploitation3: Overexploitation• Humans overharvesting

plants and animals• Commonly valuable wood

or trees are overexploited leading to extinction of tree species

• Tree exploitation can cause edge effects due to the trees extraction. This is caused because the extracted tree is generally large in comparison to surrounding trees and roads need to be cut to remove the tree. (similar with selective logging)

Overexploitation of Overexploitation of Terrestrial AnimalsTerrestrial Animals• Hunting is a problem for

many endangered large predators due to their trophy value

• Primates are exploited for bushmeat for subsistence/ protein for local populations

• Species with restricted habitats or island inhabitants are extremely vulnerable

• Example: Lemurs on Madagascar

Overexploitation of Overexploitation of Marine Life:Marine Life:

• Blast Fishing: Indiscriminately kills all marine life, including coral reefs and unknowingly endangered aquatic species

• Trawl Nets: the use of trawl nets by fishermen damage coral reefs and sponges due to the weighted net being dragged along the ocean floor. Also, sea turtles are commonly killed as a result of being trapped in the net.

4: Disruption of “Interaction 4: Disruption of “Interaction Networks”Networks”

Ecosystems depend on species interactions

Disruptions such as habitat destruction and fragmentation cause species to move into new niches possibly displacing previous inhabitants

Example: The decline of Howler monkeys with the increase of Muriquis in Brazil’s Atlantic Forest

The extinction of one species and especially a keystone species will directly cause the extinction of other species

ExtinctionsExtinctions

Pictured: Extinct, Caspian Tiger

Extinction is when the last individual of a species has died.

Historical extinctions have occurred due to meteor impacts but current extinction rates are faster now than previously.

ExtinctionsExtinctions Problems for smaller populations or a decrease in

population size Loss of Genetic Diversity

Inbreeding depression Genetic drift Lack of gene flow, if isolated populations

Demographic Fluctuations

Environmental Fluctuations Food Availability

These factors influence the Extinction Vortex

The Extinction VortexThe Extinction Vortex

Human Impact causes Human Impact causes deforestation and deforestation and

degradation to marine degradation to marine environments. This results environments. This results in global warming, climate in global warming, climate change, extinctions and a change, extinctions and a decline in biodiversity. decline in biodiversity.

How do we Conserve How do we Conserve Biodiversity?Biodiversity?