Threats to Biodiversity

Human activities

alter trophic structure, population dynamics, habitat, energy flow, nutrient cycling, & climate; Recent decades have experienced drastic acceleration of modification

Habitat Loss & Degradation

Humans have altered >50% of Earth’s terrestrial surface: deforestation & fragmentation, argiculture, urbanization

implicated in 73% of threatened species decline

Habitat conversion most severely impacts

large-bodied, wide-ranging, specialist, migratory species, endemics

Fragmentation & Deforestation

Global forest area has been cut in 1/2 over last 300 years

130,000 km^2 of tropical forest are cleared each year

50+ nations have lost 90-100% of their forest cover

alters hydrology, nutrients, microclimate

Deforestation degrades habitats

• Agriculture removes soil nutrients → reduction in primary productivity

• Nutrient addition → eutrophication (next week)

• Fire often used to clear land → CO2 release (carbon sink → source)

habitat fragmentation

Smaller habitat fragments = Higher extinction probability

Creates edge habitat that favors generalist species; Species specialized in forest interior decline (often large predators)

urbanization

More than ½ of the world population lives in urban areas

By 2030, 5 billion people will live in cities

leads to loss of species across all taxa & trophic levels and global biotic homogenization of ecological communities

aquatic habitat loss

70% of coral reefs have been damaged by human activities

40-50% of reefs (home to 1/3 of marine fish) will disappear in next 30-40 years

Freshwater threatened by dams, reservoirs, & wetland filling

Overexploitation

Occurs when harvesting (removal) of wild organisms at rates exceeding the ability of their populations to persist; Not just food: many species poached for economic value

Overexploitation most severely impacts

Species with restricted habitats (endemics, island species); Large organisms with low reproductive rates

Species Hunted to Extinction

• Dodo

• Steller’s Sea Cow

• Passenger Pigeon

• Great Auk

• Ivory Billed Woodpecker

• Carolina Parakeet

• Falklands Island Wolf

• Caribbean Monk Seal

• Tasmanian Tiger (Thylacine)

• ALMOST Northern Elephant Seals

• ALMOST Cheetahs

Fishing down the food web

As fish stocks of top trophic levels (predatory fish) decline, fisheries are now fishing lower trophic levels

poaching

illegal hunting

African elephants declining in most of Africa for last 50 years, largely because of ivory; International ban on sale of ivory had opposite of intended effect

Biological Invasions

introduced species when they have a negative ecological impact on native species; contributed to 40% of extinctions since 1750; cost billions in damage & control

• Outcompete native species for resources or habitat

• Often cause economic harm

• May consume native species

• Can introduce pathogens to naïve populations

Introduced species

moved (intentionally or accidentally) from native range to a new region by humans

Invasive species have more severe impacts on

ground-nesting birds & small mammals, poor competitors, specialists & endemics

Human-wildlife Interactions

Anthropogenic changes force species into regions where they have closer contact with humans leading to conflict & disease; threats to crops, property, livestock, & human safety → lead to persecution & decline

zoonotic diseases

¾ of emerging human diseases are transmitted to humans from other animals; Transmitted by direct or indirect contact, or an intermediate species (vector); pose risks to both health & economic stability

ex. Rabies, plague, Chagas’, salmonella, sleeping sickness, Malaria, Lyme, Nipah, ebola, zika, monkeypox, avian flu, intestinal worms

Humans (unintentionally) spread wildlife disease

Organisms become more susceptible to disease in degraded ecosystems

Habitat loss & fragmentation alters abundance and dispersal of pathogens and their host