Habitat fragmentation occurs when large contiguous habitats are divided into smaller, more isolated patches due to habitat loss. It results from both natural processes like volcanism and climate change, as well as human activities such as agriculture, urbanization, and reservoir creation. Habitat fragmentation reduces total habitat area and the interior to edge ratio of remaining patches. It isolates patches, increasing extinction risk for species due to reduced genetic diversity and migration between populations. Smaller, isolated patches also support smaller population sizes that are more vulnerable to local extinction. Habitat fragmentation is thus a major threat to biodiversity.

1. Habitatfragmentation is the process by which habitatloss results in the division of large,continuous habitats into
smaller,more isolated remnants.Thousands ofscientific studies now show unequivocal evidence for the impacts of
patch area,edge effects, patch shape complexity, isolation and landscape matrixcontraston communitystructure
and ecosystem functioning.However,striking disparities in the results ofthese studies have raised considerable
debate aboutthe relative importance of differentmechanisms underlying fragmentation effects,and even about the
utility of the ‘fragmentation’ conceptin general.Resolution ofthis debate lies in clear discrimination ofdirectversus
indirectcausal relationships among patch and landscape variables.The m ostimportantrecentadvances in our
understanding offragmentation effects all stem from recognition ofstrong context‐dependence in ecosystem
responses,including spatial context‐dependence atmultiple scales,time‐lagged population declines,trait‐dependent
species responses and synergistic interactions between fragmentation and other components ofglobal environmental
change.
Key Concepts:
 Habitatfragmentation is an umbrella term describing the complete process bywhich habitatloss results in the
division of large,continuous habitats into a greater number ofsmaller patches oflower total area, isolated from
each other by a matrix of dissimilar habitats,and is notjustthe pattern of spatial arrangementofremaining
habitat.
 Habitatloss and habitatfragmentation are notindependentdrivers ofecological change – habitatloss acts via the
change in habitat arrangement,notindependentlyof it.
 Habitatfragmentation is a landscape‐level phenomenon,and patch‐level processes (patch area,edge effects and
patch shape complexity) can only be understood within a landscape context(isolation and matrixstructure).
 A dominanteffect of increasing habitatloss is a reduction in patch area, with resulting declines in population
densityand species richness,and significantalterations to communitycomposition,species interactions and
ecosystem functioning.
 The habitatedge is not a discrete boundaryline around a patch, it is a fuzzy three‐dimensional zone that
straddles both sides ofthe patch‐matrix boundary, and the intensityof edge influence maybe variable and
asymmetrical around the physical vegetation boundary.
 Quantification of edge impactrequires explicitdiscrimination oftwo distinctcomponents ofedge influence:edge
extent (i.e. the distance over which a statistical difference in response can be detected between the matrix and
the patch) and edge magnitude (i.e.the degree of difference in response between the patch interior and the
matrix interior).
 Increasing patch shape complexity substantiallyreduces the availabilityof ‘core’ habitatarea unaffected by edge
effects.
 Patch isolation reduces population connectivityand reduces the probabilityof population persistence,but
geographic isolation is notan absolute quantityand can only be interpreted in the lightof matrix permeability,the
dispersal traits ofthe species in question and the time‐scale over which effects mightbecome apparent.
 Matrix quality and surrounding landscape composition have a dominantinfluence on population dynamics,
species diversityand ecosystem processes in habitatpatches.
 Habitatfragmentation interacts stronglywith other components ofglobal environmental change,including species
invasions,land‐use intensification and climate change.
Keywords: connectivity; context‐dependence;edge effects; habitatarea; habitatfragmentation;habitatloss;
isolation;landscape structure;matrixcontrast; patch shape
What is habitat fragmentation and how does it occur?

2. Habitat fragmentation usually occurs because of human activities such as new roads,
parking lots and housing developments. Organisms need their specifichabitat for
survival, and fragmentation is a leading threat to many terrestrial animals.
what are some of the effects of habitat fragmentation?
Fragmented habitats may be subject to the edge effect. ... Also, since habitat
fragmentation breaks the original habitat into smaller, isolated patches, movement
between these patches can become dangerous.
example
Prior to major human activity, Britain had a diverse matrix of habitats, which consisted
predominantly of forests, interspersed with wetlands, grasslands and heath. ... A decrease in
the overall area of habitat is serious enough, but when combined with fragmentation, it can
undermine the integrity of whole ecosystems.
BENIFITS
habitat corridors provide numerous benefits for plants and animals and can play a
critical role for endangered species. Habitat corridors allow movement between isolated
populations, promoting increased genetic diversity. They provide food and shelter for a
variety of wildlife and help with juvenile dispersal and seasonal migrations.
The establishment of additional habitat corridors can also benefit people, with
underpasses or overpasses for wildlife helping to reduce vehicle collisions with large
animals. For example according to State Farm Insurance, the biggest U.S. auto insurer,
there have been 2.3 million U.S. deer collisions in the past two years, up 21 percent
from five years ago. State Farm estimates that deer-vehicle accidents resulted in more
than $3.8 billion of insurance claims and driver costs alone over the past year.
Habitat corridors can also minimize interaction between humans and wildlife by allowing
predators, such as wolves and bears, to hunt for food in other locations, minimizing their
threat to people. The corridors can also serve to minimize wildlife encroachment into
human populated areas during natural disasters such as wildfires or floods.
The many benefits of habitat corridors for both wildlife and humans, coupled with the
prevailing federal support for the preservation of endangered species presents a sound
case for investment in such research initiatives.
https://www.esa.org/esablog/ecology-in-policy/habitat-corridors-help-preserve-wildlife-in-the-midst-of-
human-society/

3. Definition[edit]
The term habitat fragmentation includes five discrete phenomena:
 Reduction in the total area of the habitat
 Decrease of the interior: edge ratio
 Isolation of one habitat fragment from other areas of habitat
 Breaking up of one patch of habitat into several smaller patches
 Decrease in the average size of each patch of habitat
"fragmentation ... not only causes loss of the amount of habitat, but by creating small, isolated
patches it also changes the properties of the remaining habitat" (van den Berg et al. 2001). Habitat
fragmentation is the landscape level of the phenomenon, and patch level process. Thus meaning, it
covers; the patch areas, edge effects, and patch shape complexity.[2]
Natural causes[edit]
Evidence of habitat destruction through natural processes such as volcanism, fire, and climate
change is found in the fossil record.[1][not in citation given]
For example, habitat fragmentation of tropical
rainforests in Euramerica 300 million years ago led to a great loss of amphibian diversity, but
simultaneously the drier climate spurred on a burst of diversity among reptiles.[1]
Human causes[edit]
Habitat fragmentation is frequently caused by humans when native plants is cleared for human
activities such as agriculture, rural development, urbanization and the creation
of hydroelectric reservoirs. Habitats which were once continuous become divided into separate
fragments. After intensive clearing, the separate fragments tend to be very small islands isolated
from each other by cropland, pasture, pavement, or even barren land. The latter is often the result
of slash and burn farming in tropical forests. In the wheat belt of central western New South
Wales, Australia, 90% of the native vegetation has been cleared and over 99% of the tall grass
prairie of North America has been cleared, resulting in extreme habitat fragmentation.
Implications[edit]
One of the major ways that habitat fragmentation affects biodiversity is by reducing the amount of
suitable habitat available for organisms. Habitat fragmentation often involves both habitat
destruction and the subdivision of previously continuous habitat.[3]
Plants and
other sessile organisms are disproportionately affected by some types of habitat fragmentation
because they cannot respond quickly to the altered spatial configuration of the habitat.[4]
As the remaining habitat patches are smaller, they tend to support smaller populations of
species.[5]
Small populations are at an increased risk of a variety of genetic consequences that
influence their long-term survival.[6]
Remnant populations often contain only a subset of the genetic
diversity found in the previously continuous habitat. Processes that act upon underlying genetic
diversity such as adaptation have a smaller pool of fitness-maintaining alleles to survive in the face
of environmental change.
Populations can maintain genetic diversity through migration. In continuous habitats, migrants have
few barriers to establish themselves in suitable sites. In fragmented habitats however, the separation
between suitable sites disrupts migration, and therefore gene flow, limiting a populations capacity to
supplement the reduced genetic diversity of the remnant populations. With lower
migration, inbreeding becomes of increasing concern as the level of homozygosity increases,

4. facilitating the expression of deleterious alleles that reduce the fitness of the population
called inbreeding depression.
The percentage preservation of contiguous habitats is closely related to both genetic and species
biodiversity preservation. Generally a 10% remnant contiguous habitat will result in a
50% biodiversity loss.[7]
Habitat loss, which can occur through the process of habitat fragmentation, is considered to be the
greatest threat to species.[8]
But, the effect of the configuration of habitat patches within the
landscape, independent of the effect of the amount of habitat within the landscape (referred to as
fragmentation per se[9]
), has been suggested to be small.[10]
A review of empirical studies found that,
of the 381 reported significant effect of habitat fragmentation per se on species occurrences,
abundances or diversity in the scientific literature, 76% were positive whereas 24% were
negative.[11]
Despite these results, the scientific literature tends to emphasize negative effects more
than positive effects.[12]
Positive effects of habitat fragmentation per se imply that several small
patches of habitat can have higher conservation value than a single large patch of equivalent
size.[11]
Land sharing strategies could therefore have more positive impacts on species than land
sparing strategies.[11]
Reduced viability[edit]
Habitat fragmented by numerous roads near the Indiana Dunes National Lakeshore.
Area is the primary determinant of the number of species in a fragment[13]
and the relative
contributions of demographic and genetic processes to the risk of global population extinction
depend on habitat configuration, stochastic environmental variation and species features.[14]
Minor
fluctuations in climate, resources, or other factors that would be unremarkable and quickly corrected
in large populations can be catastrophic in small, isolated populations. Thus fragmentation of habitat
is an important cause of species extinction.[13]
Population dynamics of subdivided populations tend to
vary asynchronously. In an unfragmented landscape a declining population can be "rescued" by
immigration from a nearby expanding population. In fragmented landscapes, the distance between
fragments may prevent this from happening. Additionally, unoccupied fragments of habitat that are
separated from a source of immigrants by some barrier are less likely to be repopulated than
adjoining fragments. Even small species such as the Columbia spotted frog are reliant on the rescue
effect. Studies showed 25% of juveniles travel a distance over 200m compared to 4% of adults. Of
these, 95% remain in their new locale, demonstrating that this journey is necessary for survival.[15]
Additionally, habitat fragmentation leads to edge effects. Microclimatic changes in light, temperature
and wind can alter the ecology around the fragment, and in the interior and exterior portions of the
fragment. Fires become more likely in the area as humidity drops and temperature and wind levels
rise. Exotic and pest species may establish themselves easily in such disturbed environments, and
the proximity of domestic animals often upsets the natural ecology. Also, habitat along the edge of a

5. fragment has a different climate and favours different species from the interior habitat. Small
fragments are therefore unfavourable for species which require interior habitat.
Conservation implications[edit]
Habitat fragmentation is often a cause of species becoming threatened or endangered. The
existence of viable habitat is critical to the survival of any species, and in many cases the
fragmentation of any remaining habitat can lead to difficult decisions for conservation biologists.
Given a limited amount of resources available for conservation is it preferable to protect the existing
isolated patches of habitat or to buy back land to get the largest possible continuous piece of land. In
rare cases a conservation reliant species may gain some measure of disease protection by being
distributed in isolated habitats. This ongoing debate is often referred to as SLOSS (Single Large or
Several Small).
One solution to the problem of habitat fragmentation is to link the fragments by preserving or
planting corridors of native vegetation. In some cases, a bridge or underpass may be enough to join
two fragments.[16]
This has the potential to mitigate the problem of isolation but not the loss of interior
habitat.
Another mitigation measure is the enlargement of small remnants in order to increase the amount of
interior habitat. This may be impractical since developed land is often more expensive and could
require significant time and effort to restore.
The best solution is generally dependent on the particular species or ecosystem that is being
considered. More mobile species, like most birds, do not need connected habitat while some smaller
animals, like rodents, may be more exposed to predation in open land. These questions generally
fall under the headings of metapopulations island biogeography.