How does habitat loss affect humans

Fragmentation can lead to widespread, long-term changes in the composition and function of remaining habitat While there is an ongoing debate about the impacts of fragmentation the altered spatial configuration of habitat for a given amount of habitat loss per se 22 , recent research has reiterated the negative consequences of fragmentation itself Habitat loss is closely monitored, and in some ecosystems is tracked daily e.

In contrast, fragmentation is not explicitly tracked and is less well understood While many attempts have been made to estimate global habitat loss 1 , 12 , 24 , there is but a single estimate comparing fragmentation across biomes 20 , and none comparing against an historic baseline. We identify human-derived changes in habitat fragmentation, by comparing LIA patches to an idealized globe with no human-caused fragmentation at a global scale and on a biome-by-biome basis.

Tropical dry forests and temperate grasslands were the two most extensively converted biomes on the planet, each with less than a quarter of their extent as LIA Fig. Note that we use abbreviated names for the biomes; see Supplementary Table S1 for the full names. The majority of impacted cells have more than one impact. Biomes are ordered top-to-bottom, then left-to-right in order of increasing amount of Low Impact Area.

Similar to biomes, ecoregions varied widely in terms of the remaining proportion of LIA Fig. S1 , Table S2. Not just the extent but also the intensity of human impact varied widely. Of plots, Venter and colleagues 17 , 25 identified with low human pressure and with high pressure based on visual inspection of recent, high-resolution satellite data.

We found S2 , Table S3. We applied our data set of low human-impacted areas to assess the level of fragmentation at global and regional scales using both patch-based statistics and Euclidian distance to edge. As biomes vary naturally in their inherent level of fragmentation, we calculated a baseline level of fragmentation and the difference from this baseline to assess the impact of humans.

We identified the baseline layer using the current demarcation of land and water 26 , intersected this with biome distributions 9 , and assumed no human impact. We then compared the baseline to LIAs. Fragmentation involves the splintering of large and medium-sized patches into a proliferating number of smaller ones. At the global scale, and in nearly all biomes, the proportion of large and medium-sized patches decreased, while the smallest patches, those between 1 and 10 km 2 in size, increased Fig.

All biomes with the exceptions of tundra and boreal forest exhibited an increase in the proportion of small-sized patches relative to the overall number of patches. As the largest patches have decreased in size, not only are small fragments more common, the smallest fragments also represent a greater proportion of overall area than they did Fig.

Patch size distributions across biomes in the baseline and current Low Impact Areas. Violin plots show the probability density of the data at different values. The wider the plot, the more common the patch size. These highlight the change in the proportion of patch sizes between baseline and current Low Impact Areas, such as the loss of medium-sized patches and gain in frequency of the smallest patches in Low Impact Areas. Biomes are ordered top-to-bottom, left-to-right in order of increasing percent Low Impact Area.

Figure designed by TerraCommunications. Histograms of total contributed area from all patches within that patch size bin between the baseline and current Low Impact Areas. Several very large patches dominated baseline distributions of most biomes.

But, with the exception of the boreal and tundra biomes, the largest patches are splintered and the amount of area found in small and medium-sized patches is substantially greater in Low Impact Areas than the baseline. Biomes are ordered top-to-bottom, then left-to-right in order of increasing percent Low Impact Area. Concomitant with an increase in patch number and an increasing proportion of small patches, average patch size has decreased substantially Table 1.

Most biomes, across baseline and current LIAs, had a median patch size of 1 km 2. Smaller patch size also leads to decreases in core area.

Using a 1 km buffer to define edge vs. However, core area represents only one aspect of distance to edge; distance to edge varies continuously within a patch Fig.

Global distance to non-low impact edge. Yet, some biomes are naturally more fragmented i. Distance to edge here included both distance to biome edge including ocean coastline and to non-LIA cell to isolate the impact of human pressures.

We present a new categorical data set of human impact on the planet, Low Impact Areas, to provide an additional assessment on the feasibility of meeting expanded protected area targets on land minimally impacted by people. We used a transparent process, with the most current, open-access, publicly-available data sets to assess current human impacts across the entire terrestrial surface of the Earth not permanently covered by ice, snow, or water.

The LIAs are heavily fragmented and increasingly exposed to edge effects. While tropical dry forests had the lowest remaining percentage of LIA of all biomes, temperate grasslands exhibited the greatest fragmentation rates. We find slightly over half of land is in LIAs.

This is similar to other data sets suggesting roughly half of land is in areas minimally impacted by people 9 , 20 , Similar to Anthromes, we used a categorical process to determine whether a 1 km 2 grid cell currently has low human impacts.

If a grid cell had any urban or cropland extent, nighttime lights, or forest cover change with minor exceptions—see Methods , then it was no longer low-impact. The impacts of both human population and livestock density vary with ecosystem productivity.

All things equal, a more productive environment can support more livestock or people than an area the same size in a less productive environment Thus, in hyper-arid regions we set the threshold for impact to one person or livestock unit per km 2.

Impacts were then scaled by aridity; such that higher densities were required to move a cell from low impact to non-low impact in more humid environments but see the section on Sensitivity in Supplementary Materials. An advantage of this transparent process is that it allows identification of which and how many inputs caused a particular place to be identified as impacted. This has implications for restoration, suggesting that less than half of non-LIA land has only one type of human impact affecting it.

A further advantage of the process is that input data sets are regularly updated, in some cases yearly, and hence LIAs can be easily tracked over time. These sample areas have a median image resolution within plots of 0.

Venter and colleagues 17 found They also found Therefore, we felt confident in applying the data set to identify global fragmentation rates. Fragmentation, along with habitat loss, are together considered the primary reasons behind biodiversity loss and associated declines in ecosystem function While there is widespread agreement of the large and pernicious effects of habitat loss on biodiversity, there is less agreement on the impact of habitat fragmentation per se 22 , We do not reiterate the statements on either side of this debate but instead present the global fragmentation results side-by-side with a measure of habitat loss to review the conservation status of different biomes.

Biomes vary naturally in their baseline level of fragmentation, with some more contiguous than others. Mangroves, for instance, are spread patchily along tropical coastlines with no very large patches at the global scale.

Tundra and boreal forest are widespread biomes dominated by large patches. The tropical coniferous forests biome exists in only a few areas of the globe, and uniquely had more patches at mid-sizes than the smallest-sized patches in the baseline scenario. When comparing fragmentation rates across biomes, it is important to first consider the natural level of fragmentation in that biome, to properly assess the impact of human-caused fragmentation.

Regardless of the previous distribution of patch sizes, humanity has had a homogenizing effect across the biomes. Now, all biomes have similar distributions of patch sizes in LIAs.

This result matches the homogenization of the size distributions of tropical forest fragments across continents found by Taubert et al. Indeed, we speculate that the homogenization of patch sizes across biomes is a factor in overall biotic homogenization 32 , Both globally, and in most biomes, large patches dominated total patch area in the baseline scenario.

While still predominantly true, the current largest patches are frequently an order of magnitude smaller than the baseline, and the percentage of total area made up by the largest patches has shrunk considerably e. Much more of the remaining habitat is in small and medium-sized patches which are exposed to edge effects with less core area.

Despite this similarity across biomes, there is wide variation across biomes in the level of fragmentation caused by humans. Temperate grasslands have suffered the worst anthropogenic fragmentation of all biomes. Median distance to edge has also decreased by Tropical dry forests, tropical grasslands, Mediterranean and temperate broadleaf forest biomes have also experienced substantial decreases in average patch size, core area, increases in patch number, and decreases in median distance to edge.

With so little habitat conversion, it is unsurprising that the tundra biome has experienced the least anthropogenic fragmentation to date, although climate change threatens to rapidly modify this biome regardless of direct human impact. At the global scale, humanity has caused widespread fragmentation of terrestrial environments. Globally, average patch size has decreased by Most previous analyses looked only at fragmentation rates within a single biome or region e.

Our estimate is an underestimate as we do not include edges caused by roads. Recently, the GHM layer was used to assess global fragmentation rates across all biomes, although they only measured distance to edge. Across all biomes, we find a smaller median distance to edge than Kennedy et al. We also found differences between ranking of biomes by threat. Kennedy et al. While we also identified tropical dry forests as one of the most fragmented biomes, the other three biomes Kennedy mentioned have three of the four smallest baseline mean patch sizes by biome, suggesting that some of the fragmentation they identify is not anthropogenic in origin.

We caution that our data set of human impacts has several caveats. One caveat is that the delineation of LIAs is dependent on the use or exclusion of various data sets, such as roads see the section on Sensitivity in Supplementary Materials.

Another caveat is that we set all impacts equal to each other and there is no accumulation of impacts. We recognize that the impact of livestock on biodiversity is not equal to that from conversion to cropland 36 again, see the section on Sensitivity in Supplementary Materials. Some areas with low human impacts currently e. Thus, we do not suggest LIAs as places that still unequivocally contain intact native flora and fauna. But, it is likely that the only areas that do have intact native species assemblages are contained within LIAs.

In addition, we do not assess remaining natural intact vegetation, merely the absence of identifiable human stressors. Another complication for mangroves is that they exist in small patches on the coastline and due to variation in coastline delineation across data sets, some were ruled as NoData — see Methods. There are also a number of caveats to our fragmentation findings. First, these numbers are dependent on the baseline land and biome data we use as well as the scale of the analysis.

The baseline fragments are a result of the intersection of biome data and terrestrial land after the removal of water and permanent snow or ice. A different baseline land or water data set, along with a finer analysis scale, would find more patches.

Another important caveat is that we treat all edges the same, regardless of biome or the context of the edge see the section on Sensitivity in Supplementary Materials. Most other regional or global studies treated all edges the same 20 , 21 , 27 , but Pfeifer and colleagues 37 created a novel way to look at the intensity of the edge, or the contrast, between cells with varying amounts of forest cover.

In addition, what constitutes an edge differs between biomes e. Despite these caveats, we believe this analysis makes an important contribution towards assessing global rates of fragmentation across all biomes. Future, more nuanced, global assessments of fragmentation could vary the definition of edge by ecosystems. In conclusion, tropical dry forests and temperate grasslands stand out as the two biomes with the smallest remaining percentage of land remaining as LIAs and the greatest increases in fragmentation rates.

This confirms results that also show these biomes as some of the most threatened globally 12 , Other ways people directly destroy habitat include filling in wetlands, dredging rivers, mowing fields, and cutting down trees. Habitat fragmentation: Much of the remaining terrestrial wildlife habitat in the U. These fragments of habitat may not be large or connected enough to support species that need a large territory where they can find mates and food. The loss and fragmentation of habitats makes it difficult for migratory species to find places to rest and feed along their migration routes.

Habitat degradation: Pollution , invasive species , and disruption of ecosystem processes such as changing the intensity of fires in an ecosystem are some of the ways habitats can become so degraded, they no longer support native wildlife. Agriculture: Much of the habitat loss from agriculture was done long ago when settlers converted forests and prairies to cropland. Today, there is increasing pressure to redevelop conservation lands for high-priced food and biofuel crops.

Land conversion for development: The conversion of lands that once provided wildlife habitat to housing developments, roads, office parks, strip malls, parking lots and industrial sites continues, even during the current economic crisis.

Water development: Dams and other water diversions siphon off and disconnect waters, changing hydrology and water chemistry when nutrients are not able to flow downstream. During the dry season, the Colorado River has little to no water in it by the time it reaches the Sea of Cortez. Pollution: Freshwater wildlife are most impacted by pollution. These networks link all species interactions within communities into a single web.

For example, in a food web, when a predator eats a prey, this can have consequences for the resources used by the prey. Studies in this area have revealed that ecological networks react to habitat loss in different ways, depending on the type of interaction.

While networks of mutualistic interactions tend to break up into smaller networks , food webs tend to contract into a single smaller network.

Mutualistic interactions also tend to become weaker the species rely on each other less , while feeding relationships are stronger under habitat loss.

But while this research has confirmed that habitat destruction deeply influences the way species interact, until now we have lacked a full understanding of the effects of habitat loss on community stability. Similarly, we have not known to what extent community responses change depending on the nature of habitat loss. For our study, we looked into these issues of community stability and response using a mathematical representation of an ecological system. This model simulates interactions and changes in species populations through time in a range of different landscapes — from pristine continuous habitats to highly fragmented habitats.

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. 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 — was 3. In the humid tropics where forest loss is primarily from timber extraction, , km 2 was lost out of a global total of 11,, km 2 or 2.

In the tropics, these losses also represent the extinction of species because of high levels of endemism. In temperate and boreal regions, forest area is gradually increasing with the exception of Siberia , but deforestation in the tropics is of major concern. Sustainable practices, which preserve environments for long-term maintenance and well-being, can help preserve habitats and ecosystems for greater biodiversity.

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. 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. Overharvesting threatens biodiversity by degrading ecosystems and eliminating species of plants, animals, and other organisms.

Overharvesting, also called overexploitation, refers to harvesting a renewable resource to the point of diminishing returns. Ecologists use the term to describe populations that are harvested at a rate that is unsustainable, given their natural rates of mortality and capacities for reproduction. The term applies to natural resources such as wild medicinal plants, grazing pastures, game animals, fish stocks, forests, and water aquifers. Sustained overharvesting can lead to the destruction of the resource, and is one of the five main activities — along with pollution, introduced species, habitat fragmentation, and habitat destruction — that threaten global biodiversity today.

All living organisms require resources to survive. Overharvesting these resources for extended periods of time can deplete natural resources to the point where they are unable to recover within a short time frame. Humans have always harvested food and other resources they have needed to survive; however, human populations, historically, were small and methods of collection limited to small quantities.

Exponential increase in human population, expanding markets, and increasing demand, combined with improved access and techniques for capture, are causing the exploitation of many species beyond sustainable levels. As mentioned above, sustained overharvesting is one of the primary threats to biodiversity. Overharvesting can lead to resource destruction, including extinction at the population level and even extinction of whole species.

Depleting the numbers or amount of certain resources can also change their quality; for example, the overharvesting of footstool palm a wild palm tree found in Southeast Asia, the leaves of which are used for thatching and food wrapping has resulted in its leaf size becoming smaller. Overharvesting not only threatens the resource being harvested, but can directly impact humans as well — for example by decreasing the biodiversity necessary for medicinal resources. A significant proportion of drugs and medicines are natural products which are derived, directly or indirectly, from biological sources.

However, unregulated and inappropriate harvesting could potentially lead to overexploitation, ecosystem degradation, and loss of biodiversity; further, it can negatively impact the rights of the communities and states from which the resources are taken.