AP Environmental Science:: Unit 2 - Biodiversity

Biodiversity is best understood as encompassing three distinct levels: genetic diversity, species diversity, and ecosystem diversity. Genetic diversity specifically refers to:

- **A)** The total number of different species present within a given region or ecosystem
- **B)** The variety of genes/alleles present within a single species' population, which provides the raw material for that population to adapt to changing environmental conditions (such as new diseases or a shifting climate) via natural selection
- **C)** The variety of distinct ecosystem types (such as forests, wetlands, and grasslands) present within a given landscape or region
- **D)** A concept that has no meaningful, describable relationship to any level of biological variation at all

Species diversity, the second of the three biodiversity levels, is best measured by combining a community's species richness with its species evenness (both discussed in the previous unit). A community with high species diversity is therefore best described as one that has:

- **A)** Both a large number of different species present (high richness) and a relatively even distribution of individuals across those species (high evenness), rather than being dominated by just one or two species
- **B)** A large number of different species present but overwhelmingly dominated by just one or two of them, since species diversity specifically requires only high richness with no reference whatsoever to evenness
- **C)** Only a single dominant species present, with no other species represented in any meaningful number
- **D)** A concept that applies only to producer species, with no meaningful applicability to consumer or decomposer species

Ecosystem diversity, the third biodiversity level, refers to:

- **A)** The variety of genes/alleles present within a single species population, which is instead the definition of genetic diversity, not ecosystem diversity
- **B)** The total number of individual organisms present within a single ecosystem
- **C)** A concept that has no meaningful, describable relationship to the variety of ecosystem or habitat types present in a region
- **D)** The variety of distinct ecosystem/habitat types (such as forests, wetlands, coral reefs, and grasslands) present within a given region or landscape - a region with many different ecosystem types generally supports a correspondingly wider overall range of species and genetic diversity than a region dominated by just one ecosystem type

An endemic species is best defined as a species that:

- **A)** Is found in every ecosystem on Earth, with no meaningful geographic restriction of any kind
- **B)** Has already gone fully extinct, with no living individuals remaining anywhere
- **C)** Is found naturally in only one specific, relatively limited geographic region and nowhere else on Earth - island ecosystems (such as Madagascar or the Galapagos Islands) often harbor an especially high proportion of endemic species, precisely because their geographic isolation has allowed unique evolutionary lineages to develop that are not found anywhere else
- **D)** Was deliberately introduced by humans into a region outside its natural historical range

A biodiversity hotspot, as formally defined by conservation scientists, is a geographic region that meets which of the following two specific criteria?

- **A)** Contains no endemic species at all, and has experienced no habitat loss of any kind
- **B)** Contains an unusually large number of endemic species (at least 1,500 endemic plant species, under the most widely used formal definition) AND has already lost a very significant proportion (at least 70%) of its original natural habitat, making it both irreplaceable and urgently threatened
- **C)** Is located exclusively within a tropical rainforest biome, with no meaningful applicability to any other biome type
- **D)** Has the single largest total human population density of any region on Earth

Habitat destruction/loss is widely considered the single leading overall driver of species extinction and biodiversity decline worldwide, primarily because it:

- **A)** Directly eliminates the physical space, food resources, and shelter that a species' population depends on for survival and reproduction - when enough of a species' habitat is destroyed or degraded (through processes such as deforestation, wetland draining, or urban development), the remaining population may become too small or too fragmented to persist long-term
- **B)** Only affects producer species, with no meaningful impact on any consumer species
- **C)** Has no meaningful, describable relationship to species survival, reproduction, or population size of any kind
- **D)** Affects every species on Earth completely equally and uniformly, with no meaningful variation in impact between different species or regions

The set of major human-caused threats to biodiversity is sometimes summarized with the acronym HIPPCO, standing for Habitat destruction, Invasive species, Population growth (human), Pollution, Climate change, and Overharvesting. Under this framework, "invasive species" specifically threaten native biodiversity primarily by:

- **A)** Always going extinct immediately upon introduction to a new ecosystem, since an ecosystem lacking natural predators for the new species would inherently be hostile to its survival
- **B)** Only threatening producer species, with no meaningful threat to consumer species of any kind
- **C)** Outcompeting native species for shared limited resources and/or preying heavily on native species that have no evolved defenses against them (as discussed in the previous unit's coverage of the competitive exclusion principle and trophic cascades), often with especially severe effects on geographically isolated island ecosystems whose native species evolved without any comparable competitors or predators present
- **D)** Having no meaningful, describable relationship to native species survival, competition, or predation of any kind

Under the HIPPCO framework for major biodiversity threats, "overharvesting" refers to:

- **A)** A threat that applies only to producer/plant species, with no meaningful applicability to any animal species
- **B)** A form of pollution specifically caused by excess fertilizer runoff, rather than accurately describing a distinct, separate threat category from pollution itself
- **C)** A threat that has no meaningful, describable relationship to population size, extinction risk, or human harvesting activity of any kind
- **D)** Harvesting individuals of a wild species (through hunting, fishing, logging, or collection) at a rate faster than that species' population can naturally replace itself through reproduction, which can drive population declines and, in severe cases, extinction - historical examples include the extinction of the passenger pigeon and the near-extinction of many whale species due to commercial whaling