8.6 Biodiversity

• Learning Objectives
• Describe the relationship between ecosystem diversity and its resilience to changes in the environment
• Explain how the addition or removal of any component of an ecosystem will affect its overall short-term and long-term structure

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What is biodiversity?

• Species Diversity
• Number of species in an ecosystem
• Genetic Diversity
• Variety of traits (alleles) in a population
• Ecosystem Diversity
• Presence of different species filling the various niches
• components of an ecosystem

Number of described species. There are about 1.8 million described species, with insects making up over half of them. Estimates range between 10 and 50 million total species on Earth.

Why biodiversity?

• Natural and artificial ecosystems with fewer component parts and with little diversity among the parts are often less resilient to changes in the environment
• Ecosystem diversity refers to the variety of ecosystems in a region
• e.g. Coral reefs vs. monoculture ocean areas

Eagles and bears feed on spawning salmon. Humans introduced the opossum shrimp as prey for salmon. Instead, the shrimp competed with salmon for zooplankton as a food source. The salmon, eagle, and bear populations subsequently declined.

Case Study – Rainforest vs. Grassland

• Rainforests generally exhibit greater biodiversity than grasslands
• tropical rainforests are known for harboring a vast number of species
• plant and animal species
• Grasslands are less diverse in terms of total species
• can have high plant diversity within smaller areas

Keystone Species

• Definition
• A species that has a disproportionate impact on ecosystem structure and function
• Impact
• Removing them can cause trophic cascades or ecosystem collapse

Keystone Species

• Sea Otters (Kelp forests)
• Wolves (Yellowstone)
• Beavers (Wetland creation)
• Pollinators (Bees)

Biodiversity Hotspot

• Regions with exceptionally high biodiversity and significant threats
• Criteria
• At least 1,500 endemic plant species
• Lost ≥70% of original habitat
• Examples: Amazon, Madagascar, Coral Triangle

HUMAN Impact on Biodiversity > HIPPO+C

• Habitat destruction
• Invasive species
• Pollution
• Population (humans)
• Overharvesting/Overexploitation
• +Climate Change

Lionfish are an invasive species in the Caribbean.

Exotic species. a. Kudzu, a vine from Japan, was introduced into several southern states to control erosion. Today, kudzu has taken over and displaced many native plants. Here it has engulfed an abandoned house. b. Mongooses were introduced into Hawaii to control rats, but they also prey on native birds.

1. Turtles for sale. In 2011, during a religious holiday in Dhaka, Bangladesh, over 100,000 turtles were butchered for consumption. Large numbers of wild-caught tortoises and freshwater turtles are offered for sale at markets in East Asia. Shown here are steppe tortoises (Testudo horsefieldii) and elongated tortoises (Indotestudo elongata)
2. Aquaculture farms. Red-eared slider turtles (Trachemys scripta elegans) are now raised in aquaculture farms. Although this takes pressure off wild turtle populations, such turtles reinforce the habit of turtle consumption and can become invasive species when they escape into the wild.

Habitat loss. a. In a study that examined records of imperiled U.S. plants and animals, habitat loss emerged as the greatest threat to wildlife. b. Macaws that reside in South American tropical rain forests are endangered for many of the same reasons listed in the graph in (a).c. Habitat loss due to road construction in Brazil. Top: Road construction opened up the rain forest and subjected it to fragmentation. Middle: The result was patches of forest and degraded land. Bottom: Wildlife could not live in destroyed portions of the forest.

Loss of Ecosystem Components

• Short-Term Effects
• Disruption of food chains
• Population imbalances
• Long-Term Effects
• Ecosystem collapse
• Loss of services (pollination, water purification)
• Example
• Removing wolves from Yellowstone
• elk overgrazing → erosion = loss of habitat for many species