Lecture 24: Conservation Biology (Chapter 22/23)
Case Study: Can Birds and Bombs Coexist?
• Could it be that using land as a bombing range has been the secret to conservation success? Although it may
seem weird, decades of bombing on the Fort Bragg military base in the North Carolina Sandhills have
inadvertently protected thousands of acres of longleaf pine savanna, aiding efforts to save endangered red
• Figure 22.1: The RedCockaded Woodpecker: An Endangered Species:
o A female redcockaded woodpecker approaching her nest hole. This species was once abundant
throughout the pine savannas (communities dominated by grasses intermixed with pine trees) of the
US, but has been severely reduced in numbers due to the loss of its required habitat. Among the
various types of pine savanna, longleaf pine savanna is the redcockaded woodpecker’s preferred
• For 90 years, the forests of Fort Bragg have been used for military training exercises, degraded by offroad
vehicles and earthmoving equipment, and set on fire by explosives. These activities take place in the midst
of a vibrant but now uncommon ecosystem one that, ironically, survives in large part as a result of military
o First, pine savanna depends on fire for its persistence, so the fires that result from explosions
benefit rather than harm the ecosystem.
o Second, the designation of large blocks of forest land for
military use has kept them from being converted to
farmland, forest plantations, and residential uses.
• While some longleaf pine savanna has been preserved at Fort Bragg
and other military bases, overall, this ecosystem has been reduced only
3% of the more than 35 million hectares it once covered.
o Figure 22.2: Decline of the longleaf pine savanna ecosystem:
(A) The estimated area covered by longleaf pine savanna at
different times. (B) As seen in this photo from the
southeastern US, longleaf pine savanna consist of open
forest with a grass understory.
• Various factors contributed to the decline, including rapid growth of the human population, the clearing of
land for large populations where other tree species, such as loblolly pine, are grown, and fire suppression.
With the decline of the longleaf ecosystem, several plant, insect and vertebrate species undergone substantial
• One of the species affected is the redcockaded woodpecker, a small insectivorous bird that is well adapted to
large tracts of open pine savanna. It was once abundant, but not the species currently stands at about 6100
breeding pairs and their associated helpers.
• These redcockaded birds are cooperative breeders, in which two to four males born to the breeding pair in
previous years typically help their parents raise young. Other woodpeckers nest in dead snags, redcockaded
woodpeckers require mature, living pine trees, especially longleaf pine, for their nesting cavities.
• Periodic fibers historically helped to maintain longleaf pine savanna. Without those fires, the longleaf pine
community soon undergoes succession.
• Redcockaded woodpeckers abandon their nesting cavities, apparently due to a decrease in food resources. In
the past, the birds would move to parts of the forest that had been more recently burned, there are fewer and
fewer places for the birds to go. This loss of habitat has reduced their populations, making them vulnerable to
problems of small, isolated populations.
• Hurricane Hugo killed 70% of the birds in one population.
• West Nile virus has not yet been detected in this species, but it is highly lethal to other birds.
• When species rely on a specific habitat that is destroying by human activities, they are found in diminishing
numbers until, in some cases, they vanish.
• The story of the redcockaded woodpecker reflects that of thousands of other imperiled species around the
• Legal protection and extraordinary human effort have resulted in stabilization and slow recovery. • Do we have a responsibility to protect biodiversity? How can we allocate limited resources for conservation?
• Over the years, as human populations has grown and increased its use of resources, the species that evolved
in the ecosystem around us have lost their habitats through their outright destruction or through changes in
their biological or physical properties. These changes have given rise to a biodiversity crisis.
• The most recent Red List of Threatened Species, compiled by the international Union for Conservation of
Nature (IUCN), lists 16913 species as threatened with extinction about 1% of all species worldwide (Table
22.1). This number is an underestimate.
• Threats to biodiversity: The natural Pyrenean Ibex, a female named Cecila, was found dead on January 6,
2000, apparently killed by a falling tree.
• Figure 22.5: Humans have been causing extinctions for millennia:
o Trends over time in (A) the total number of bird species
Figure 22.5: First top point on left:
Fossils were used to estimate the
number of species on the island
3000 years ago.
• Figure 22.3: The Passenger Pigeon: From great abundance to extinction:
o The passenger pigeon, once one of the most abundant birds in North America, was subject to
massive hunts in the 19 century.
o The last passenger pigeon died in the Cincinnati Zoo in 1914.
o The ecological effects of its extinction on the eastern deciduous forest, coincident with the loss of
the American chestnut, are difficult to estimate, but are presumed to be considerable.
• Why protect life? How to do it?
22.1 Conservation Biology
• Conservation biology is an integrative discipline that applies to the principles of ecology to the protection of
biodiversity. • Stabilization of redcockaded woodpecker populations required expertise from several biological disciplines,
as well as law, political science, and sociology.
• Determining a successful management plan involved working with farmers, landowners, the US military, and
the business community.
• Such an integrative approach is a characteristic of Conservation biology the scientific study of phenomena
that affect the maintenance, loss, and restoration of biodiversity.
• 1915: the ecological society of America is formed. There was a disagreement about its mission: Should it
exist only to support ecologists and publish research or should It also pursue an agenda to preserve natural
• 1917: from the activist wing within the Ecological Society, the committee for the Preservation of Natural
Conditions is created.
• 1946: The Committee reforms itself as the Ecologists’ Union, resolving to take “direct action” to save
threatened natural areas.
• 1950: The Ecologists’ Union changes its name to The Nature Conservancy.
Protecting biodiversity is important for both practical and moral reasons
• People rely on nature’s diversity.
• In addition to the hundreds of domesticated species that sustain us, we make abundant use of wild species for
food, fuel, and fiber.
• The natural functioning of biological communities provides valuable services to humans. All of us are
dependent on a wide range of these ecosystem services, such as water purification, generation and
maintenance of soils, pollination of crops, climate regulation, and flood control.
• These lifesustaining functions are themselves dependent on the integrity of nature communities and
• For some people, biodiversity has inherent value and warrants protection simply for that reason.
The field of conservation biology arose in response to global diversity losses
• Scientist has long been aware that human activity negatively affects the abundances and distributions of
• Conservation biology emerged as a scientific discipline in the early 1980s as ecologists and other scientists
saw the need to apply their knowledge to the preservation of species and ecosystems.
Conservation biology is a valuebased discipline
• The scientific method calls for objectivity collection and interpretation of data without bias.
• Many ecologists have chosen to speak up or refocus their research programs, as they have come to
understand the biological consequences of the changes taking place on their planet.
22.2 Declining Biodiversity
• Biodiversity is declining globally, and Earth’s biota is becoming increasingly homogenized.
• The tropical botanist devoted his life to identifying, classifying, and mapping the immense diversity of plants
in Central and South America.
o He was an eyewitness to plant species extinctions as deforestation rapidly destroying habitat.
o It was not uncommon for him to identify a new endemic plant species (a plant species that occurs in
a particular geographic region and nowhere else) during an expedition to Ecuador or Peru, only to
return to the same spot a few years later to find the forest cleared and species gone.
• Figure 22.2: Loss of forest cover in western Ecuador
o Between 1958 and 1988, a growing human population and government policies that served to
stimulate rapid economic development led to rapid deforestation in western Ecuador.
o Green indicates forest cover. o The extensive loss of forest habitat in this region is estimated to have resulted in the loss of more
than 1000 endemic species.
Earth’s biota is becoming increasingly homogenized
• Organisms move above; they always have, and always will.
• Over the last century, however, people have moved over the Earth’s surface at an unprecedented rate,
carrying organisms with them and greatly enhancing rates of introductions of new species to all parts of the
• These range expansions coincide with the range contractions of many native species whose numbers are
declining due to habitat loss and other factors. Typically, the greatest “losers” among the native species tend
to be specialists those with morphological, physiological, or behavioral adaptations to a particular habitat
while the “winners” tend to be generalists with less stringent habitat requirements.
• The spread of introduced species and native generalists, coupled with declining abundances and distributions
of native specialists, are part of a growing taxonomic homogenization of Earth’s Biota.
• Taxonomic homogenization: the worldwide reduction of biodiversity resulting from the spread of non
native and native generalists coupled with declining abundances and distributions of native specialists and
• Island biotas are particularly vulnerable to both extinction and invasion. The decline of island endemics is
often accelerated by the introduction of more cosmopolitan species.
22.3 Threats to Biodiversity
• The primary threats to biodiversity are habitat loss and degradation, invasive species, overexploitation,
pollution, disease, and climate change.
• Understanding the causes of biodiversity losses is the first step toward reversing them.
• For any given species, multiple factors are likely to contribute to decline and extinction.
• The ecological footprint of humanity of Earth is large and rapidly increasing.
o 83% of the land surface has been modified in some way.
o Homo sapiens is now appropriating 1055% of Earth’s primary production and has appropriated
98% of the area where wheat, corn, or rice can be grown.
o Figure 22.9: Habitat Loss Results from a Growing Human Footprint
Habitat Loss and degradation are the most important threats to biodiversity
• Earth has been modified across 60% of its land surface, and all marine ecosystems have been affected by
humans is now appropriating between 10% and 55% of Earth’s primary production. • The influence of human activities on natural habitat is the most important factor contributing to global
declines in biodiversity.
• There are areas of extreme human influence, such as agricultural regions and certain coastal waters, and areas
of little human influence, such as deserts and some polar seas.
• Habitat degradation: changes that reduced quality of the habitat for many, but not all species.
• Habitat fragmentation: breaking up of continuous habitat into habitat patches amid a humandominated
• Habitat Loss: conversion of an ecosystem to another use.
• Habitat degradation is extremely widespread. It has diverse causes and takes many forms.
Invasive Species can displace native species and alter ecosystem properties
• Invasive Species: nonnative, introduced species that sustain growing populations and have large effects on
o Of a particular concern are invasive species that impact native endangered species.
• Invasive species are of particular concern where they complete with, prey on, or change the physical
environment of endangered native species.
• The effect of the Eurasian zebra mussel on the freshwater mussel species of North American is a prime
o Prior to invasion, zebra mussels were already in trouble. Most of these species are globally
imperiled, many are endemic and thus naturally rare, and are all threatened by compromised water
quality and river channelization.
o After the zebra mussel introduction, competition brought about steep declines in native freshwater
mussels (6090%), including some regional extinction.
• In many ecosystems, habitat fragmentation is followed by habitat degradation, which increases vulnerability
to invasive species.
• Example: Tropical dry forests of Hawaii have been reduced 90%. This habitat has 25% of Hawaii’s
threatened plant species.
o An invasive species of fountain grass has led to further ecosystem degradation.
o It has outcompeted and displaced native plants, and increased fire frequency.
• Invasive predators can also contribute to extinction.
o In Lake Victoria, introduction of the Nile perch has reduced the diversity and abundance of the
native cichlid fishes.
o 600 species of cichlids have been recorded, most of which are endemic to the lake.
o The Nile perch is a large predator, and its introduction into the lake in the 1960s has contributed to
the extinction of about 200 cichlid species.
o Before the introduction, cichlids ma