AP Biology

## Learning Outcomes

- Explain why biodiversity can increase the stability of ecological communities after environmental change.
- Distinguish among genetic diversity, species diversity, and habitat diversity.
- Use Simpson’s Diversity Index to compare biodiversity between communities.
- Describe in situ and ex situ conservation strategies, including their benefits and limits.
- Explain how habitat fragmentation, invasive species, overharvesting, and climate change can reduce biodiversity.
- Predict how conservation actions affect population size, gene flow, and extinction risk.
- Apply experimental design and data-analysis skills to conservation biology scenarios.

## AP Biology Syllabus

In AP Biology Unit 8, conservation strategies are tested through the broader ideas of ecological interactions, biodiversity, population change, and disruptions to biological communities. Questions often ask you to connect conservation actions to natural selection, gene flow, population growth, community interactions, or data from graphs and tables.

- Biodiversity includes genetic, species, and habitat-level variation.
- Greater biodiversity can help a community withstand or recover from environmental disruptions.
- Simpson’s Diversity Index can be used to quantify and compare biodiversity.
- Human activities can change population size, species interactions, nutrient cycling, and habitat availability.
- Conservation strategies may act by increasing habitat area, reducing mortality, increasing reproduction, or maintaining genetic variation.
- AP questions may ask you to identify controls, variables, hypotheses, and appropriate graphs in conservation investigations.
- Free-response questions often require evidence-based claims about population trends, extinction risk, or the success of a management plan.

## Test Your Knowledge

Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, look more closely at that area during your revision.

1. Why might a community with high species evenness be more stable than one dominated by a single species?
2. What does Simpson’s Diversity Index measure, and how does the value change as diversity increases?
3. How can habitat corridors reduce the effects of habitat fragmentation?
4. Why is genetic diversity an important goal in captive breeding programs?
5. What experimental controls would be needed to test whether removing an invasive predator increases native bird nesting success?

## Introduction

Conservation biology applies ecology, evolution, genetics, and data analysis to protect biodiversity. In AP Biology, you are not expected to memorize every conservation program in the world. Instead, you should be able to explain the biological logic of a strategy: what problem it addresses, what variable it changes, and how it affects survival, reproduction, gene flow, or community stability.

A strong answer links a conservation action to a biological mechanism. For example, “planting trees” is vague. A better AP-level explanation is: restoring native vegetation increases nesting sites and food sources for native insects and birds, which can increase reproductive success and population size. Conservation strategies are often evaluated using population data, species counts, genetic data, or biodiversity indices.

> **Key Term: Biodiversity**
> The variety of life in a given area, including variation among genes, species, and habitats.

### Measuring biodiversity and setting conservation priorities

Biodiversity is not just the number of species present. A community with 10 species may still have low diversity if one species makes up nearly all individuals. AP Biology questions may ask you to compare biodiversity using species richness, species evenness, or Simpson’s Diversity Index.

> **Key Term: Species richness**
> The number of different species present in a community or study area.
>
> **Key Term: Species evenness**
> A measure of how evenly individuals are distributed among the species present.

Suppose two forest plots each contain four tree species. In Plot A, each species has 25 individuals. In Plot B, one species has 97 individuals and the other three species have 1 individual each. Both plots have the same species richness, but Plot A has greater evenness and therefore greater overall diversity.

One AP Biology formula used for biodiversity is Simpson’s Diversity Index:

\text{Simpson's Diversity Index} = 1 - \sum \left(\frac{n}{N}\right)^2
where $$n$$ is the number of individuals of one species and $$N$$ is the total number of individuals of all species in the study area.

> **Key Term: Simpson’s Diversity Index**
> A biodiversity measure that accounts for both species richness and species evenness; higher values indicate greater diversity.

A value closer to 1 usually indicates higher diversity. A value closer to 0 indicates lower diversity, often because one species dominates the sample.

For example, imagine a small sample contains 10 organisms:

- Species A: 5
- Species B: 3
- Species C: 2

The index is:

$$
1 - \left[\left(\frac{5}{10}\right)^2 + \left(\frac{3}{10}\right)^2 + \left(\frac{2}{10}\right)^2\right]
= 1 - (0.25 + 0.09 + 0.04)
= 0.62
$$

If another site has the same total number of organisms but all 10 are from one species, the index is:

$$
1 - \left(\frac{10}{10}\right)^2 = 0
$$

This comparison shows why both richness and evenness matter.

> **Test Tip:**
> When using Simpson’s Diversity Index, do not just count species. Use the number of individuals in each species. A community with more equal abundances will usually have a higher index than one dominated by a single species.

Conservation priorities often focus on places with high biodiversity, many endemic species, rapidly declining populations, or unique habitats. However, AP Biology questions usually give you the needed context. If a prompt describes a rare amphibian that only breeds in one wetland, a conservation strategy should address that species’ breeding habitat, water quality, and population size rather than giving a generic answer such as “protect nature.”

Biodiversity can help communities resist or recover from disruptions. If several species perform similar roles, the loss of one species may be partly compensated by others. Genetic variation within a population can also increase the chance that some individuals possess alleles that help them survive a new disease, pollutant, or climate shift.

### In situ conservation: protecting species in their habitats

In situ conservation protects organisms where they naturally live. This is often the preferred strategy because it protects species along with the interactions they depend on, such as pollination, predation, seed dispersal, competition, and nutrient cycling.

> **Key Term: In situ conservation**
> Conservation that protects species within their natural habitats.

Examples include national parks, marine reserves, wildlife refuges, protected wetlands, and community-managed forests. These areas can reduce habitat loss, hunting, fishing pressure, pollution, or human disturbance. In AP Biology, focus on the mechanism: protected areas can increase survival and reproduction by preserving food sources, shelter, nesting sites, and breeding grounds.

Protected areas are most effective when they are large enough to support viable populations. Small isolated reserves may not contain enough resources, mates, or genetic variation. They may also be more affected by edge effects.

> **Key Term: Habitat fragmentation**
> The division of a large continuous habitat into smaller, separated patches.

Fragmentation can reduce biodiversity by isolating populations. Isolated populations may have reduced gene flow, smaller population sizes, and higher risk of inbreeding. A road, farm field, dam, or urban area can separate populations that previously exchanged individuals and alleles. Over time, reduced gene flow can lower genetic diversity and increase extinction risk.

One strategy for fragmentation is creating habitat corridors.

> **Key Term: Wildlife corridor**
> A strip or connection of suitable habitat that allows organisms to move between separated habitat patches.

Corridors can allow migration, recolonization, access to mates, and gene flow. For example, a forested corridor between two woodlots may allow small mammals, insects, or birds to move safely between them. This can increase genetic exchange and reduce the chance that a local population disappears after a disturbance.

However, conservation strategies often involve trade-offs. Corridors can also allow the spread of disease, parasites, predators, or invasive species. On the AP exam, a strong response may mention both a benefit and a possible cost if the question asks for evaluation.

> **Exam Warning:**
> Do not assume every conservation strategy has only positive effects. AP Biology often rewards answers that recognize trade-offs, such as corridors increasing gene flow but also possibly increasing disease spread.

In situ conservation can also include sustainable harvesting. If humans rely on fish, timber, or wild animals, management may aim to keep harvest below the rate at which populations can replace themselves. Population models can be relevant here. If births exceed deaths, a population may grow; if deaths exceed births, it declines. Conservation plans may reduce death rates by limiting harvest, creating closed seasons during breeding periods, or protecting juveniles until they reproduce.

Protected areas may also focus on keystone species.

> **Key Term: Keystone species**
> A species whose effect on community structure is greater than expected based only on its abundance.

Protecting a keystone predator, pollinator, or habitat-forming organism can indirectly protect many other species. For example, if a predator limits an herbivore population, removing the predator may allow herbivores to overconsume plants, affecting insects, birds, and nutrient cycling. Conservation of the predator can help maintain community structure.

### Ex situ conservation and genetic management

Ex situ conservation protects organisms outside their natural habitats. It is especially useful when a species is at immediate risk from habitat destruction, poaching, disease, or very small population size.

> **Key Term: Ex situ conservation**
> Conservation that protects species outside their natural habitats, such as in zoos, aquariums, botanical gardens, seed banks, or captive breeding programs.

Examples include captive breeding, seed banks, sperm and egg banks, tissue collections, and botanical garden propagation. These methods can preserve individuals or genetic material while threats in the original habitat are reduced.

Captive breeding programs aim to increase population size and, when possible, reintroduce individuals into the wild. A successful program must manage genetic diversity carefully. If only a few individuals reproduce, allele frequencies may shift by chance, and rare alleles may be lost.

> **Key Term: Genetic diversity**
> The variety of alleles and genotypes within a population or species.

Genetic diversity matters because it gives natural selection variation to act on. A genetically uniform population may be highly vulnerable to a disease or environmental change. A genetically varied population has a better chance that some individuals will survive and reproduce when conditions change.

Small populations are especially vulnerable to genetic drift and bottlenecks.

> **Key Term: Population bottleneck**
> A sharp reduction in population size that can reduce genetic variation by chance.

After a bottleneck, the surviving individuals may not represent the genetic diversity of the original population. Even if the population later increases in number, lost alleles may not return unless mutation or gene flow introduces them. This is why conservation biologists often track pedigrees in captive breeding programs to avoid mating close relatives and to maintain as many alleles as possible.

> **Test Tip:**
> If an AP question asks why conservationists care about genetic diversity, connect it to evolution: more genetic variation increases the chance that some individuals have traits that improve survival or reproduction under changing conditions.

Ex situ methods have limits. Captive individuals may adapt to artificial conditions, lose behaviors needed in the wild, or become dependent on humans. Reintroduction can fail if the original threat has not been removed. For example, breeding a fish species in captivity will not restore the population if the river remains polluted or blocked by dams.

Seed banks are an important ex situ method for plants. Seeds can be stored for future germination, preserving alleles from crop relatives or endangered plant species. This can matter for food security and restoration because wild relatives of crops may contain alleles for drought tolerance, disease resistance, or salt tolerance.

Zoos and aquariums can support conservation through breeding programs, research, education, and funding. However, they cannot house every threatened species, so decisions often prioritize species with severe risk, high ecological importance, unique evolutionary history, or realistic reintroduction potential.

### Restoration, invasive species control, and evidence-based decisions

Conservation is not only about preventing damage; it can also involve restoring damaged habitats. Restoration attempts to return a degraded area toward a healthier state by reestablishing native species, improving water or soil quality, removing pollutants, or rebuilding physical habitat.

> **Key Term: Ecological restoration**
> The process of assisting the recovery of a damaged or degraded biological community.

Examples include replanting native vegetation after mining, restoring wetlands that were drained for agriculture, removing dams to allow fish migration, or reintroducing native grazers. AP Biology questions may ask you to predict outcomes. If native plants are restored, herbivorous insects that depend on them may increase, followed by insect-eating birds. If wetlands are restored, amphibian breeding success may increase because more suitable aquatic habitat becomes available.

Invasive species control is another major conservation strategy.

> **Key Term: Invasive species**
> A nonnative species that spreads in a new area and causes harm to native species, habitats, or human interests.

Invasive species can reduce biodiversity through competition, predation, disease transmission, hybridization, or habitat alteration. For example, an invasive plant may outcompete native plants for light and nutrients, reducing food and habitat for native insects. An invasive predator may reduce prey populations that lack defenses against it.

Control methods include physical removal, chemical treatment, biological control, hunting or trapping, quarantine, and public education. Each method has risks. Chemical treatment may harm non-target species. Biological control, such as introducing a predator or parasite, can itself become a problem if it attacks native species. AP Biology answers should show cause-and-effect reasoning, not just name a method.

> **Exam Warning:**
> Avoid saying that introduced species are always invasive. A nonnative species becomes invasive when it spreads and causes harm. Some introduced species do not become major threats.

Evidence-based conservation uses data to decide whether a strategy is working. AP Biology may present a graph of population size before and after a protected area is created, or a table comparing species counts in restored and unrestored plots. You may be asked to identify the independent variable, dependent variable, control group, or a reasonable conclusion.

For example, to test whether removing an invasive rat increases seabird nesting success, researchers might compare nesting success on islands where rats are removed with similar islands where rats remain. The independent variable is rat removal. The dependent variable could be the percentage of nests producing fledglings. Constants might include survey timing, nest-counting methods, and study duration. A control group is needed because seabird numbers could also change due to weather, food supply, disease, or ocean temperature.

Good conservation experiments often use replication. A single restored pond and a single unrestored pond are weak evidence because differences may be due to chance or local conditions. Multiple restored and control sites provide stronger support. Error bars or 95% confidence intervals can help evaluate whether observed differences are likely meaningful.

> **Test Tip:**
> In conservation data questions, read axes, units, and labels carefully. If a graph shows percentages, values usually cannot exceed 100%, and categories may need to add to 100% if they represent all possible groups.

Climate change adds another challenge because it can shift temperature, rainfall, ocean acidity, sea level, and seasonal timing. Conservation strategies may include protecting climate refuges, increasing habitat connectivity so species can move, restoring carbon-storing habitats such as forests and wetlands, or preserving genetic variation that may allow adaptation. Be careful with claims: individual organisms do not evolve because they “need to.” Populations evolve when allele frequencies change across generations due to selection, mutation, gene flow, or genetic drift.

Conservation biology often combines multiple strategies. For a threatened frog, a plan might include wetland protection, disease monitoring, captive breeding, reintroduction, invasive predator removal, and public limits on habitat disturbance. In an AP free-response answer, you do not need to list every possible action. Choose one or two, then explain the biological mechanism clearly.

## Key Point Checklist

This article has covered the following key knowledge points:

- Biodiversity includes genetic variation, species variation, and habitat-level variation.
- Greater biodiversity can help a biological community resist or recover from environmental disruption.
- Species richness counts the number of species, while species evenness describes how equally individuals are distributed.
- Simpson’s Diversity Index uses both richness and evenness; higher values generally indicate greater diversity.
- In situ conservation protects organisms in their natural habitats.
- Habitat fragmentation can isolate populations, reduce gene flow, and increase inbreeding risk.
- Wildlife corridors can increase movement and gene flow but may also spread disease or invasive species.
- Ex situ conservation includes captive breeding, seed banks, botanical gardens, and genetic storage.
- Genetic diversity is important because it provides variation for natural selection.
- Population bottlenecks can reduce genetic variation even if population size later increases.
- Invasive species can reduce biodiversity through competition, predation, disease, or habitat alteration.
- Conservation claims should be supported with data, controls, variables, and clear cause-and-effect reasoning.

## Key Terms and Concepts

- Biodiversity
- Species richness
- Species evenness
- Simpson’s Diversity Index
- In situ conservation
- Habitat fragmentation
- Wildlife corridor
- Keystone species
- Ex situ conservation
- Genetic diversity
- Population bottleneck
- Ecological restoration
- Invasive species


Biodiversity - Conservation strategies