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47.3A: Habitat Loss and Sustainability - Biology

47.3A: Habitat Loss and Sustainability - Biology



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Through increased adoption of sustainable practices, we can reduce habitat loss and its consequences.

Learning Objectives

  • Describe the effects of habitat loss to biodiversity and concept of sustainability

Key Points

  • Habitat destruction renders entire habitats functionally unable to support the species present; biodiversity is reduced in this process when existing organisms in the habitat are displaced or destroyed.
  • Clearing areas for agricultural purposes is the main cause of habitat destruction; other principal causes include mining, logging, and urban sprawl.
  • The primary cause of species extinction worldwide is habitat destruction.
  • Sustainability is a term that describes how biological systems remain diverse and productive over time, creating the potential for long-term maintenance of human well-being.
  • Reducing negative human impact requires three concepts: environmental management, management of human consumption of resources, and awareness of cultural and political concerns to increase sustainability.

Key Terms

  • sustainability: Configuring society so that each person can meet their own needs and greatest potential, while preserving biodiversity and natural ecosystems, and planning for future generations to maintain this potential.
  • endemism: The ecological state of a species being unique to a defined geographic location, such as an island, nation, country or other defined zone, or habitat type; organisms that are indigenous to a place are not endemic to it if they are also found elsewhere.
  • biodiversity: The diversity (number and variety of species) of plant and animal life within a region.

Habitat Loss

Humans rely on technology to modify their environment and replace certain functions that were once performed by the natural ecosystem. Other species cannot do this. Elimination of their ecosystem – whether it is a forest, a desert, a grassland, a freshwater estuary, or a marine environment – will kill the individuals within most species. Remove the entire habitat within the range of a species and, unless they are one of the few species that do well in human-built environments, the species will become extinct.

Effects of Habitat Loss on Biodiversity

Habitat loss is a process of environmental change in which a natural habitat is rendered functionally unable to support the species present. This process may be natural or unnatural, and may be caused by habitat fragmentation, geological processes, climate change, or human activities such as the introduction of invasive species or ecosystem nutrient depletion. In the process of habitat destruction, the organisms that previously used the site are displaced or destroyed, reducing biodiversity.

Human destruction of habitats has accelerated greatly in the latter half of the twentieth century. Natural habitats are often destroyed through human activity for the purpose of harvesting natural resources for industry production and urbanization. Clearing habitats for agriculture, for example, is the principal cause of habitat destruction. Other important causes of habitat destruction include mining, logging, and urban sprawl. Habitat destruction is currently ranked as the primary cause of species extinction worldwide.

Consider the exceptional biodiversity of Sumatra. It is home to one sub-species of orangutan, a species of critically endangered elephant, and the Sumatran tiger; however half of Sumatra’s forest is now gone. The neighboring island of Borneo, home to the other sub-species of orangutan, has lost a similar area of forest, and forest loss continues in protected areas. The orangutan in Borneo is listed as endangered by the International Union for Conservation of Nature (IUCN), but it is simply the most visible of thousands of species that will not survive the disappearance of the forests of Borneo. The forests are being removed for their timber, and to clear space for plantations of palm oil, an oil used in Europe for many items including food products, cosmetics, and biodiesel.

A five-year estimate of global forest cover loss for the years 2000–2005 was 3.1 percent. In the humid tropics where forest loss is primarily from timber extraction, 272,000 km2 was lost out of a global total of 11,564,000 km2 (or 2.4 percent). In the tropics, these losses also represent the extinction of species because of high levels of endemism.

Since the Neolithic Revolution, about 47% of the world’s forests have been lost to human use. Present-day forests occupy about a quarter of the world’s ice-free land, with about half of these occurring in the tropics. In temperate and boreal regions, forest area is gradually increasing (with the exception of Siberia), but deforestation in the tropics is of major concern.

Feeding more than seven billion human bodies takes a heavy toll on the earth’s resources. This begins with the appropriation of about 38 percent of the earth’s land surface and about 20 percent of its net primary productivity. Added to this are the resource-hungry activities of industrial agribusiness: everything from crops’ need for irrigation water, synthetic fertilizers, and pesticides, to the resource costs of food packaging, transport (now a major part of global trade), and retail.

Sustainability

Sustainability is a concept that describes how biological systems remain diverse and productive over time. Long-lived and healthy wetlands and forests are examples of sustainable biological systems. For humans, sustainability is the potential for long-term maintenance of well-being, which has ecological, economic, political, and cultural dimensions. Sustainability requires the reconciliation of environmental, social, and economic demands, which are also referred to as the “three pillars” of sustainability.

Healthy ecosystems and environments are necessary for the survival and flourishing of humans and other organisms, and there are a number of ways to reduce humans’ negative impact on the environment. One approach is environmental management, which is based largely on information gained from earth science, environmental science, and conservation biology. A second approach is management of human consumption of resources, which is based largely on information gained from economics. A third, more recent, approach adds cultural and political concerns into the sustainability matrix.

Loss of biodiversity stems largely from the habitat loss and fragmentation produced by human appropriation of land for development, forestry and agriculture as natural capital is progressively converted to human-made capital. At the local human scale, sustainability benefits accrue from the creation of green cities and sustainable parks and gardens. Similarly, environmental problems associated with industrial agriculture and agribusiness are now being addressed through such movements as sustainable agriculture, organic farming, and more-sustainable business practices.


Urban expansion dynamics and natural habitat loss in China: a multiscale landscape perspective

China's extensive urbanization has resulted in a massive loss of natural habitat, which is threatening the nation's biodiversity and socioeconomic sustainability. A timely and accurate understanding of natural habitat loss caused by urban expansion will allow more informed and effective measures to be taken for the conservation of biodiversity. However, the impact of urban expansion on natural habitats is not well-understood, primarily due to the lack of accurate spatial information regarding urban expansion across China. In this study, we proposed an approach that can be used to accurately summarize the dynamics of urban expansion in China over two recent decades (1992-2012), by integrating data on nighttime light levels, a vegetation index, and land surface temperature. The natural habitat loss during the time period was evaluated at the national, ecoregional, and local scales. The results revealed that China had experienced extremely rapid urban growth from 1992 to 2012 with an average annual growth rate of 8.74%, in contrast with the global average of 3.20%. The massive urban expansion has resulted in significant natural habitat loss in some areas in China. Special attention needs to be paid to the Pearl River Delta, where 25.79% or 1518 km(2) of the natural habitat and 41.99% or 760 km(2) of the local wetlands were lost during 1992-2012. This raises serious concerns about species viability and biodiversity. Effective policies and regulations must be implemented and enforced to sustain regional and national development in the context of rapid urbanization.

Keywords: China biodiversity ecoregions natural habitat loss nighttime light urban expansion.


47.3A: Habitat Loss and Sustainability - Biology

Despite the habitat loss that has occurred globally to date, there is still hope. Studies reveal that by protecting 50 percent of the land and ocean around the world, plant and animal species could thrive.

A highland ranforest stream in Ankaratra that provides critically important habitat for endangered amphibians. Photo Credit: Jonathan Kolby

Habitat destruction is one of the biggest threats facing plants and animal species throughout the world. The loss of habitat has far-reaching impacts on the planet’s ability to sustain life, but even with the challenges, there is hope for the future.

Habitat destruction, defined as the elimination or alteration of the conditions necessary for animals and plants to survive, not only impacts individual species but the health of the global ecosystem.

Habitat loss is primarily, though not always, human-caused. The clearing of land for farming, grazing, mining, drilling, and urbanization impact the 80 percent of global species who call the forest home. Approximately 15 billion trees are cut down each year. According to a study about tree density published in Nature , the number of trees worldwide has decreased by 46 percent since the start of civilization. In addition to the loss of habitat, deforestation reduces the ability of forests to provide the critical benefit of absorbing carbon, which helps to mitigate the effects of climate change.

The situation is even worse in waterways, coastal areas, and the ocean. Coastal estuaries and marshes provide breeding grounds for the majority of marine species. As they, along with inland wetlands, are dredged and filled, species are less able to birth and support their young. Pollution and effluents from the land travel easily through streams and rivers to the ocean, where they impact the health of fish, birds, and marine plants. Deforestation far from shore can cause erosion that enters the water and deposits silt into the shallow marine waters, blocking the sunlight that coral reefs need to survive.

Despite the habitat loss that has occurred globally to date, there is still hope. Studies reveal that by protecting 50 percent of the land and ocean around the world, plant and animal species could thrive. Today, only 15 percent of the land and 7 percent of the ocean is protected, leaving us with a challenging yet attainable goal.

The Campaign for Nature calls upon world leaders to take action in helping to protect 30 percent of the Earth’s land and ocean by 2030, on the way to 50 percent of the planet in a natural state by 2050. This commitment represents our best opportunity to preserve the ecosystems necessary for our survival.


47.3A: Habitat Loss and Sustainability - Biology

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The role of fragmentation experiments

Field-based fragmentation experiments are critical in expanding our understanding of habitat fragmentation. Ranging in spatial scale from 2 × 10 −7 ha to 100 ha, the most commonly recognized fragmentation experiments cover a broad range of ecological communities (Fig. 1 Haddad et al. 2015). In contrast to observational studies, these projects have careful, a priori, experimental designs with significant levels of replication and known initial conditions, allowing for powerful inferences. Few however approach the scale at which contemporary land management and conservation planning must address fragmentation.

Map of long-term fragmentation experiments as identified in Haddad et al. (2015) with the addition of Thousand Island Lake, clockwise from top-left: 1 Kansas Fragmentation Project (KFP). Located in Kansas, USA, KFP is an experimentally fragmented prairie ecosystem, focusing on the impacts of fragmentation on community assembly and successional processes. 2 Moss fragmentation experiments (MFE). Consisting of a wide range of projects carried out simultaneously in both the UK and Canada, MFE includes both field and laboratory experiments, which have focused on a broad array of processes, including fragmentation per se, corridor effectiveness, and the interactions between fragmentation and climate change. 3 Metatron. Perhaps the most technically complex and flexible fragmentation experiment, Metatron, located in south central France, consists of independent patches which can be connected or disconnected via experimentally controlled corridors, allowing for the study of multiple landscape configurations. 4 Thousand Island Lake (TIL). Described in detail in the text, TIL combines both community assembly and relaxation processes across more than 1000 remnant islands. 5 Wog Wog Habitat Fragmentation Experiment (WWHFE). Located in Southeastern Australia, WWHFE was designed to study the effects of habitat fragmentation on biological diversity in an Eucalyptus forest. 6 Stability of Altered Forest Ecosystems (SAFE) Project. Located in the rainforests of Malaysian Borneo, SAFE is composed of multiple projects that investigate how forest modification gradients (e.g., land use and cover patterns) and forest fragmentation affect biodiversity, ecological processes, and waterways. 7 Biological Dynamics of Forest Fragments Project (BDFFP). Located in the Brazilian Amazon, BDFFP is the world’s largest and longest-running habitat fragmentation experiment, conducting a wide range of forest fragmentation effects on biodiversity and ecosystem processes. 8 Savannah River Site Corridor Experiment (SRSCE). Located in South Carolina, USA, SRSCE was designed to study the effects of corridors on plant and animal dispersal, population persistence, and biodiversity in a managed forest

One challenge is to bridge the gap between scales feasible for direct experimental manipulation, and larger scales which are the domain of conservation, restoration, and management. Large-scale infrastructure projects can at times provide inadvertent, unplanned experiments which can be utilized to fill this gap in scales. For example, in Venezuela, Professor John Terborgh creatively utilized the creation of Lago Guri, a large (>4000 km 2 ) man-made hydroelectric lake dotted with hundreds of forested islands, to demonstrate the dramatic importance of trophic cascades in tropical forest (Terborgh et al. 2001). Unfortunately, the draining of the lake destroyed the integrity of the study, and combined with political uncertainties, research there is not ongoing.

Another promising large-scale, unplanned experiment, comparable in some ways to Lago Guri, which can fill the gap between standard fragmentation experiments and large spatial scales is the ongoing project at Thousand Island Lake (TIL). Formed in 1959 TIL is a large, man-made lake in Chun’an County of Zhejiang Province, China. TIL has total water surface of approximately 580 km 2 and 1078 land-bridge islands when the maximum water level (108 m.a.s.l.) (Figure 1 Wang et al. 2009). During dam construction, primary forests in the region were selectively or clear-cut with organized logging during the “Great Leap Forward.” This resulted in near complete deforestation before the lake’s inundation. Airplanes then sowed native pines, possibly affecting soil pH or causing allelopathy that could have lasting effects on regional biotas. This region is now protected as one of the largest national parks in China. The majority of the islands (erstwhile hilltops) have not experienced significant human disturbance since 1962. In concert, these reasonably consistent initial conditions combined with a history of ecological monitoring and the opportunity for very high levels of replication, allow the TIL system to avoid many of the pitfalls that plague other “natural” fragmentation experiments. This history also ensures that TIL will combine aspects of relaxing and assembling ecosystems, in that the original understory community was not directly removed, and the removal of trees would set into motion successional dynamics as recolonization occurs from external seed sources.

Studies at TIL have already provided the building blocks necessary to answer many of the questions proposed above, providing insights into the recovery patterns of avian, mammalian, reptilian, and plant communities in fragmented landscapes. A suite of studies, focusing on both plant and animal communities, have shown that island area plays the dominant role in controlling community recovery on TIL’s islands. On the species and gene levels, plant, bird, snake, and small mammal communities have clear relationships with island area, but not island isolation (Wang et al. 2010, 2011, 2012b Hu et al. 2011 Zhang et al. 2012 Ding et al. 2013 Si et al. 2014, 2015a Su et al. 2014 Yuan et al. 2015). There are some notable exceptions to the trend of area effects dominating isolation effects (e.g., Wang et al. 2012a Yu et al. 2012 Peng et al. 2014). That said, when taken as a whole these results suggest that patch area may be a more significant factor in community assembly than patch isolation in this system. Ongoing research is underway to dissect the specific mechanisms by which this process occurs (e.g., Hu et al. 2015 Si et al. 2015b).

The opportunity for comparison between TIL to other large scale fragmentation experiments is promising. Because the communities of TIL are primarily assembling, direct comparisons to other assembling communities such as the Kansas Fragmentation Experiment (e.g., Cook et al. 2005) could provide insights into whether successional processes in fragmented landscapes are consistent across biomes. Used together, systems in which matrix quality remains constant can compare to large-scale experiments in which matrix quality varies, such as the Biological Dynamics of Forest Fragments Project (e.g., Laurance et al. 2011), to address questions concerning edge contrast. Naturally, there are many other opportunities for comparison. We expect the TIL project to play a critical role in fragmentation research over the coming decades, while also proving a platform for international collaborations.

Fragmentation studies in the past have enabled us to understand a wide range of effects of habitat loss and fragmentation on biodiversity and ecological processes, but fundamental questions remain. These questions span spatial, temporal, and organizational scales, and they necessitate new approaches and techniques. With a focus on identifying ecologically relevant drivers, we are confident that answering these questions will provide scientists and practitioners with the scientific basis and tools necessary to promote biodiversity and landscape sustainability.