Conservation Biology and Global Change
Protecting Species Threatened by Human Activities
Protecting the diversity of life involves:
Restoring or preserving habitats.
Preventing and managing the introduction of non-native species.
Establishing networks of protected areas.
Combating climate change and other human-caused environmental changes.
Harvesting populations sustainably.
Human Activities Threatening Earth's Biodiversity
Human activities are altering ecosystem processes globally.
More than 75% of Earth’s terrestrial ecosystems have been transformed.
Conservation biology integrates various fields of biology to conserve diversity at all levels.
Current extinction rates are 100 to 1,000 times higher than typical rates seen in the fossil record.
Human activities threaten Earth’s biodiversity at all levels.
Three Levels of Biodiversity
Biodiversity can be considered at three main levels:
Genetic diversity: Variation within and between populations.
Species diversity: Number of species in an ecosystem or the biosphere.
Ecosystem diversity: Variety of ecosystems in the biosphere.
Genetic Diversity
Genetic diversity includes the genetic variation within a population and between populations.
Population extinctions reduce genetic diversity, which in turn reduces the adaptive potential of the entire species.
Species Diversity
Species diversity is the number of species in an ecosystem or across the biosphere.
An endangered species is at risk of extinction throughout all or a significant portion of its range.
A threatened species is likely to become endangered in the near future.
As of 2023, more than 42,100 species (28%) are threatened (IUCN).
In the United States, out of 20,000 known plant species, 200 have become extinct, and 730 are endangered or threatened (Center for Plant Conservation).
At least 123 freshwater animal species have gone extinct since 1900, and hundreds more are threatened.
Local extinction is the loss of a species in a specific geographic area.
Global extinction means a species is lost from all ecosystems where it lived.
The local extinction of one species can negatively impact other species in an ecosystem.
Flying foxes (bats) are important pollinators and seed dispersers in the Pacific Islands.
Ecosystem Diversity
Human activity is reducing ecosystem diversity, the variety of ecosystems in the biosphere.
More than 50% of wetlands in the contiguous United States have been drained and converted to agricultural or other uses.
Biodiversity and Human Welfare
There are moral and philosophical reasons to care about the loss of biodiversity:
Our sense of connection to nature (biophilia).
The belief that other species are entitled to life.
Concern for future generations.
Benefits of Species and Genetic Diversity
Species and genetic diversity have practical benefits.
Wild populations can provide genetic variation for breeding desirable qualities into crop plants.
In the United States, 25% of prescriptions contain substances originally derived from plants.
The rosy periwinkle contains alkaloids that inhibit cancer growth.
The loss of a species results in the loss of unique genes that may code for proteins useful to humans.
Taq polymerase, the enzyme used in the PCR reaction, was extracted from a bacterium.
Ecosystem Services
Ecosystem services are all natural ecosystem processes that help sustain human life:
Purification of air and water.
Detoxification and decomposition of wastes.
Crop pollination, pest control, and soil preservation.
Earth’s ecosystem services are estimated to be worth $33 trillion per year but are provided for free.
Threats to Biodiversity
The four major types of threats to biodiversity caused by human activities are:
Habitat loss
Introduced species
Overharvesting
Global change
Habitat Loss
Alteration of habitat is the greatest threat to biodiversity.
Contributing factors include agriculture, urban development, forestry, mining, and pollution.
Habitat loss and fragmentation can occur over immense regions.
Smaller populations are more vulnerable to extinction, reducing the number of species in fragmented regions.
Prairie areas in Wisconsin lost 8–60% of their diversity following the transition to crop land.
Habitat loss is also a major threat to aquatic biodiversity.
Coral reefs, among the most species-rich aquatic communities, have experienced significant loss.
About 50% of reef-building corals were lost from 1957 to 2007.
Freshwater habitats are being lost due to dams, reservoirs, channel modification, and flow regulation.
Introduced Species
Introduced species are those that humans move from native locations to new geographic regions.
Without their native predators, parasites, and pathogens, introduced species may spread rapidly.
Introduced species may disrupt their adopted communities through predation or competition.
Many species introductions have had damaging ecosystem effects.
Zebra mussels introduced to the Great Lakes threaten native species and damage infrastructure.
Burmese pythons introduced by the exotic pet trade in the Everglades coincide with declines of over 90% in several mammal species.
Intentional introductions with good intentions can have disastrous effects.
Kudzu, an Asian plant introduced to the southern United States to control soil erosion, has taken over large areas of the landscape.
Introduced species have contributed to about 40% of worldwide extinctions recorded since 1750.
The impact of introduced species costs billions of dollars in damage and control efforts each year.
Overharvesting
Overharvesting is the harvesting of wild organisms at rates exceeding the population’s ability to rebound.
Species with restricted habitats or large body sizes with low reproductive rates are vulnerable to overharvesting.
African elephant populations have only stabilized where they have been protected from hunting for nearly a century.
DNA analysis helps conservation biologists identify the source of illegally obtained animal products.
DNA from illegally harvested ivory can be used to trace the original population of elephants to within a few hundred kilometers.
Overfishing rapidly decimates wild fish populations.
In just 10 years, the western Atlantic bluefin tuna population was reduced to less than 20% of its 1980 size.
Global Change
Global change includes alterations in climate, ocean and atmospheric chemistry, and broad ecological systems.
Burning wood and fossil fuels causes sulfuric and nitric acid to form in the atmosphere.
The resulting acid precipitation (pH < 5.2) is harmful to many organisms.
Environmental regulations have helped decrease acid precipitation.
Sulfur dioxide emissions in the United States decreased by >75% between 1990 and 2013, gradually reducing the acidity of precipitation.
Population Conservation
Biologists focusing on conservation at the population and species levels follow two main approaches:
Focus on small, vulnerable populations.
Emphasize critical habitat.
Extinction Risks in Small Populations
Small populations are vulnerable to overharvesting, habitat loss, and other biodiversity threats.
Small population size itself can push the population to extinction.
The Extinction Vortex
Inbreeding and genetic drift draw small populations down an extinction vortex into smaller and smaller sizes.
Inbreeding and genetic drift cause a loss of the genetic variation required for evolutionary responses to change.
Inbreeding further reduces fitness by increasing the frequency of homozygosity of harmful recessive alleles.
Some populations can persist with low genetic variability.
Low genetic variability does not automatically lead to permanently small populations.
Northern elephant seals have rebounded from 20 individuals to about 150,000 despite low genetic variation.
Case Study: The Greater Prairie Chicken
North American populations of the greater prairie chicken were fragmented by agriculture in the 1900s.
A massive population decline to less than 50 in Illinois was associated with decreased fertility.
Scientists increased genetic variation by importing 271 birds from larger populations elsewhere.
The declining population rebounded, confirming that low genetic variation caused an extinction vortex.
Minimum Viable Population Size
Minimum viable population (MVP) is the minimum population size at which a species can survive.
Estimates of MVP depend on many factors that affect a population’s chances for survival.
The number of individuals likely to be killed in a natural catastrophe such as a storm.
Effective Population Size
Total population size can be misleading; only breeding individuals pass their alleles to offspring.
Effective population size provides a meaningful estimate of MVP based on breeding potential.
Effective population size () is estimated by , where and are the number of females and males that breed successfully, respectively.
is always a fraction of the total population.
Case Study: Analysis of Grizzly Bear Populations
In 1800, about 100,000 grizzly bears ranged over 500 million ha in the United States.
Today, 1,000 bears live in six isolated populations over less than 5 million ha.
In 1978, population viability analysis was conducted on the bears in and around Yellowstone National Park.
Life history data collected over a 12-year period was used to simulate effects of various environmental factors.
Given suitable habitat, viability models predicted:
95% chance of 70–90 bears surviving for 100 years.
95% chance of 100 bears surviving for 200 years.
The Yellowstone population includes about 700 bears, but the effective population size is about 175.
The Yellowstone grizzly population has low genetic variability compared with other grizzly populations.
Introducing individuals from other populations would increase the numbers and genetic variation.
Promoting dispersal between fragmented populations is an urgent conservation need.
Critical Habitat and Population Decline
Loss of critical habitat can cause decline of threatened populations, even above the minimum viable population size.
Focus on critical habitat emphasizes environmental factors responsible for population decline.
Recognizing key habitat factors and restoring habitat can support viable populations.
Case Study: Decline of the Red-Cockaded Woodpecker
Red-cockaded woodpeckers require living trees in mature pine forests with little undergrowth to block flight paths.
Breeding birds will abandon nests if undergrowth exceeds about 4.5 m in height.
Logging, agriculture, and fire suppression have caused population declines by reducing suitable habitat.
Red-cockaded woodpeckers take months to excavate new nesting cavities.
Experiments indicate that they are more likely to use habitat sites with human-constructed nest cavities.
Controlled burn of undergrowth and excavation of nesting cavities is used to maintain habitat promoting species recovery.
Weighing Conflicting Demands
Species conservation requires resolution of conflict between the needs of species and human demands.
In the western United States, habitat preservation for many species is at odds with grazing and resource extraction industries.
The ecological role of the target species is an important consideration in conservation.
Identifying and conserving populations of keystone species can maintain community and ecosystem diversity.
Landscape and Regional Conservation
Historically, conservation efforts have focused on saving individual species.
Today, conservationists seek to sustain the biodiversity of entire communities, ecosystems, and landscapes.
Landscape Structure and Biodiversity
The physical structure of a landscape can strongly influence biodiversity.
Many species use more than one type of ecosystem or live in the borders between ecosystems.
Fragmentation and Edges
The boundaries, or edges, between ecosystems are defining features of landscapes.
Abiotic conditions in edges are distinct from those in the surrounding landscapes.
Some species take advantage of edge communities to access resources from both adjacent areas.
Fragmentation increases edge habitat and reduces overall biodiversity, though edge-adapted species may thrive.
White-tailed deer browse on woody shrubs near forest edges.
Their populations expand following forest logging.
Parasites adapted to edge habitat can put further pressure on already vulnerable populations.
Brown-headed cowbird populations increase following forest fragmentation.
They lay eggs in the nest of the host, often migratory songbirds, and reduce host reproductive success.
Cowbird parasitism and habitat loss are correlated with a decline in several host species.
The Biological Dynamics of Forest Fragments Project in the Amazon examines the effects of forest fragmentation on community structure.
Results consistently show that species adapted to the forest interior decline in small patches.
Landscapes dominated by small fragments will likely support fewer species.
Corridors That Connect Habitat Fragments
A movement corridor is a narrow strip or series of clumps of habitat connecting otherwise isolated patches.
Movement corridors promote dispersal and reduce inbreeding in small, fragmented populations.
Corridors are important for species that migrate between different habitats seasonally.
Riparian habitats bordering streams and rivers form natural corridors for species dispersal.
Artificial corridors can be constructed in areas of heavy human use to protect species and increase gene flow.
Urban Ecology
Urban ecology examines organisms and their environment in urban settings.
Remaining fragments of wild areas become incorporated into urban landscapes as cities expand.
These fragments connect isolated populations and provide “stepping stone” pathways for migration.
Human populations also benefit from the services of urban ecosystems, such as air and water purification.
Establishing Protected Areas
As of 2023, 16% of terrestrial and freshwater habitats and 8% of marine habitats worldwide have been protected.
The global community is working to reach a goal of protecting 30% of global ecosystems by 2030.
The design, placement, and management of protected areas are controversial topics in conservation biology.
Preserving Biodiversity Hot Spots
Biologists often focus on biodiversity hotspots when prioritizing areas for conservation.
A biodiversity hot spot is a relatively small area with many endemic, endangered, and threatened species.
Collectively, about a third of all plant, amphibian, reptile, and mammal species reside on <1.5% of Earth’s land.
Focus on hot spots for placement of nature reserves has drawbacks:
Selection is often biased for vertebrates and plants but neglects invertebrates and microorganisms.
Emphasizes a small fraction of Earth’s surface.
Changing climate complicates identification of conditions that will be favorable in the future.
Philosophy of Nature Reserves
Nature reserves are protected “islands” of biodiversity in a sea of habitat altered or degraded by human activity.
Successful nature reserves allow natural disturbance to occur as a functional component of the ecosystem.
Periodic burning is necessary to maintain fire-dependent communities, such as tallgrass prairie.
An important conservation question is whether to create many small reserves or fewer large reserves.
A network of small reserves protects more habitat types and diffuses the risk of loss due to natural disturbance.
Large reserves have reduced edge habitat and support far-ranging, low-density animal populations.
Zoned Reserves
A zoned reserve includes relatively undisturbed areas surrounded by human-modified areas of economic value.
Buffer zones are created by regulating human activities in areas surrounding the protected core.
The key challenge is developing a social and economic climate in the buffer compatible with the long-term viability of the core.
Costa Rica is a world leader in establishing zoned reserves, divided into 11 Conservation Areas.
Buffer zones provide forest products, water, hydroelectric power, and support sustainable agriculture and tourism.
Many fish populations have collapsed worldwide due to technological advances in fishing practices.
Networks of marine reserves increase fish populations within the reserve and improve fishing success nearby.
This zoned reserve practice has been applied to marine ecosystems for centuries in the Fiji Islands.
The Florida Keys National Marine Sanctuary was created in 1990 to protect marine ecosystems.
Many species of fish and lobsters recovered quickly.
Abundant fish populations expanded into nearby reefs, improving fishing outside the sanctuary.
Increased marine life in the reserve attracted recreational divers.
Earth Is Changing Rapidly
The locations of reserves today may be unsuitable for their species in the future.
Three types of environmental change that threaten biodiversity include:
Nutrient enrichment
Toxin accumulation
Climate change
Nutrient Enrichment
Harvesting depletes nutrients from agricultural soils; fertilizer is applied to replace nutrients, such as nitrates.
Excess nitrates leach from soil after plants are removed.
Human activities have more than doubled the supply of fixed nitrogen available to primary producers.
Critical load is the amount of added nutrient that can be absorbed by plants without damaging ecosystem integrity.
Nutrients exceeding critical load leach into groundwater or runoff into aquatic ecosystems.
Phytoplankton productivity increases, causing blooms.
Decomposition of excess phytoplankton depletes dissolved oxygen, resulting in aquatic “dead zones.”
Toxins in the Environment
Humans release many toxic chemicals, including synthetics previously unknown in nature.
Harmful substances accumulate in fat and other tissues and concentrate in organisms at higher trophic levels.
Biological magnification occurs because the biomass at any trophic level is produced from larger biomass ingested from the previous level.
Industrial Compounds and Pesticides
Chlorinated hydrocarbons include PCBs (polychlorinated biphenyls) and many pesticides, such as DDT.
They are subjected to biological magnification.
Herring gulls in the Great Lakes lay eggs with PCB levels 5,000 times those in phytoplankton at the base of the food web.
In the 1960s, Rachel Carson brought attention to the biomagnification of DDT in birds in her book Silent Spring.
Population declines in several birds of prey were linked to DDT bioaccumulation.
DDT interfered with eggshell formation, causing thin shells that broke under the parents' weight.
Affected bird populations recovered following the 1971 ban of DDT in the United States.
Pharmaceuticals
Pharmaceutical drugs enter freshwater ecosystems through human and animal waste and improper disposal.
Chronic exposure to low concentrations of sex steroids can have large effects on aquatic species.
Estrogen used in birth control pills causes feminization of male fathead minnows.
Plastic Waste
Plastics, synthetic compounds made from petroleum products, are the most common type of marine debris.
About 4.8–12.7 million metric tons of plastic waste enter the ocean each year.
Large pieces are broken down over time, creating microplastics, particles less than 5 mm in size.
Plastic has wide-ranging impacts on marine life.
Many animals mistake plastic debris for food and consume fatal amounts.
Bacterial pathogens “hitchhike” on plastic waste and spread to coral reef communities.
Larger plastic waste gets entangled on reefs, damaging or depriving corals of light.
Microplastics contaminate the world’s oceans and freshwater ecosystems.
They have been found in organisms at all levels in the food chain, including humans.
Harmful effects have been documented in fish and invertebrates.
Greenhouse Gases and Climate Change
Climate change is a directional change to the global climate that lasts for 30 years or more.
This change is correlated with the accumulation of and other greenhouse gases in the atmosphere.
Human activities, including deforestation and burning fossil fuels, contribute to increasing concentration.
By 2020, the atmospheric concentration had increased by more than 50% since the mid-19th century.
Methane, water vapor, and other greenhouse gases absorb and radiate infrared radiation back toward Earth.
This is the greenhouse effect that keeps the Earth’s surface at a habitable temperature.
Rising concentrations of and other greenhouse gases are linked to increasing global temperature.
So far, Earth has warmed by an average of since 1900.
2014–2022 were the warmest years on record as of 2023.
Wind and precipitation patterns are also shifting, and the frequency of extreme weather events is increasing.
Biological Effects of Climate Change
Many organisms will not be able to disperse rapidly enough to survive climate change.
Changes in the fossil pollen record following the last ice age can help us predict future effects.
Determine dispersal rate of plant species following glacial retreat 16,000 years ago.
Climate change has caused range shifts in many species from diverse habitats.
Expected range shifts include moves to higher latitudes, greater altitudes, or greater depths.
Some species are adjusting their ranges more readily than others.
Motile animals can move more readily than nonmotile organisms.
Sessile species shift their range through dispersal of offspring; the rate depends on generation time.
A lack of suitable habitat can impede range shifts.
An animal on a mountaintop cannot shift to a higher elevation.
Factors other than temperature impact suitable habitat.
Many plants have moved to lower elevations to escape reduced precipitation.
Northern coniferous forest and tundra ecosystems have been most greatly impacted by climate change.
Melting ice exposes dark ground surfaces that absorb more radiation and warm further.
Summers in the Arctic sea without ice are predicted within decades.
Some Arctic regions are shifting from sinks to sources.
Higher temperatures, decreased snowfall, and increasing summer dry periods are damaging western coniferous forests.
Fires are more common in drought-stressed forests.
Fires have burned twice the usual area in the boreal forests in recent decades.
Climate change has effects on all levels of biological organization from cells to ecosystems.
Effects on Cells
Rising temperature affects the rate of enzymatic reactions, which can affect rates of DNA replication, cell division, and other key processes.
Climate change can impair cellular defense mechanisms.
Pine trees produce less resin and are more vulnerable to infection by mountain pine beetles.
Effects on Individual Organisms
Overheating due to increasing temperatures can lead to reduced food intake and reproductive failure.
An American pika will die if its body temperature rises above its resting temperature.
Effects on Populations
Changes in the timing of growth, reproduction, and migration occur in some species but not others.
Mismatch between interacting species can reduce survival or reproductive success.
Caribou migration is out of sync with the emergence of plants they depend upon for food.
Effects on Communities and Ecosystems
Climate change has altered primary production and nutrient cycling in ecosystems.
It can also cause dramatic changes in communities when species move to new locations.
Range expansion can have catastrophic effects on communities.
Warming has caused the sea urchin, Centrostephanus rodgersii, to expand its range.
It feeds on kelp and has destroyed kelp bed habitat and community diversity in its expanded range.
The climate change that has already occurred has had wide-ranging effects on ecosystems worldwide.
Direct effects of climate change can cause cascading indirect biological changes that are difficult to predict.
Modeling Climate Change
Global models predict that Earth’s temperature will rise by by the end of the 21st century.
Models are constructed using data on factors that affect the absorption of solar radiation at Earth’s surface.
An 11-year solar cycle and volcanic explosions affect the absorption of solar radiation.
Many human activities affect the absorption of solar radiation.
Burning fossil fuels contributes to emissions and increases absorption of solar radiation, causing warming.
Other activities decrease the absorption of solar radiation and reduce global temperature.
Dust stirred up by plowing fields or release of sulfur oxide emissions.
Scientists use computer models to organize the data and predict Earth’s temperature.
Models are becoming accurate enough to reproduce observed past changes in global warming.
Climate models are used to perform “if-then” thought experiments to predict change under different scenarios.
If we continue with emissions at current levels, by 2100, the temperature will rise above what it was in 1900.
If we stop all emissions immediately, temperature will rise to higher by 2100 than it was in 1900.
Finding Solutions to Address Climate Change
Global warming can be slowed by reducing energy consumption and converting to renewable energy.
Stabilizing emissions will require international effort and change in lifestyles and industrial processes.
Reduced deforestation would also decrease greenhouse gas emissions.
In 2015, all nations agreed to take steps to reduce emissions and limit the rise in global temperature.
The Paris Climate Accord has been ratified by 169 nations, including all major greenhouse gas emitters.
United Nations reports in 2021 and 2022 indicate that governments are not on target to meet their goals.
The Human Population
Global environmental problems arise from growing consumption and the increasing size of the human population.
No population can grow indefinitely, and humans are no exception.
The Global Human Population
The human population increased relatively slowly until about 1650 and then began to grow exponentially.
It is now >8 billion people and is increasing by more than 70 million each year.
It is predicted to increase to 9.7 billion by 2050.
Though the global population is still growing, the rate of growth has slowed since the 1960s.
Human population growth is now slower than expected in exponential growth.
Population dynamics due to disease, including AIDS and COVID-19, have impacted the growth rate.
Social change and voluntary population control have also contributed.
The growth rates of individual nations vary with their degree of industrialization.
Most of the current global population growth is concentrated in less industrialized countries.
Human population growth rates can be controlled through family planning, voluntary contraception, and increased access to education for females.
Global Carrying Capacity
The most important ecological issue today is the future size of the human population.
How many humans can the biosphere support?
Estimates of Carrying Capacity
The human carrying capacity of Earth is uncertain.
Estimates have varied from 1 billion to more than 1 trillion, with an average of 10–15 billion.
Methods for estimating carrying capacity take different factors into account, such as area of habitable land, average yield of crops, and number of calories required.
Limits on Human Population Size
The ecological footprint concept summarizes the aggregate land and water area needed to sustain a person, city, or nation.
It is one measure of how close we are to the carrying capacity of Earth.
Countries vary greatly in footprint size and available ecological capacity.
The human carrying capacity could potentially be limited by food, space, nonrenewable resources, or buildup of wastes.
Unlike other organisms, we can regulate our population growth through social changes.
Sustainable Development
The concept of sustainability helps ecologists establish long-term conservation priorities.
Sustainable Development
Sustainable development is development that meets the needs of people today without limiting the ability of future generations to meet their needs.
Connections between life sciences, social sciences, economics, and humanities must be made to achieve sustainable development.
Case Study: Sustainable Development in Costa Rica
Conservation success in Costa Rica has required partnership between government, nongovernmental organizations (NGOs), and private citizens.
Human living conditions (infant mortality, life expectancy, and literacy rate) in Costa Rica have improved along with ecological conservation.
The Future of the Biosphere
Our modern lives differ greatly from those of our hunter-gatherer ancestors.
Our behavior reflects remnants of our ancestral attachment to nature and the diversity of life—the concept of biophilia.
Our sense of connection to nature may motivate realignment of our environmental priorities.