Implications

Image obtained from pictify.com

The implications of habitat fragmentation are incredibly numerous, and perhaps not completely understood at this time.  Here I aim to relay the most discussed effects of habitat fragmentation on biodiversity among conservation biologists in no particular order of severity.  Biodiversity can simply be defined as "The variety of all living organisms, at all levels of organization." -Meade Krosby Ph.D.

Initial exclusion

Initial exclusion seems to be an appropriate place to start, as the effects of initial exclusion are the easiest to immediately identify.  Initial exclusion is the loss of species that occupied the area that was altered in some way to cause the fragmentation.  These species' habitats are literally at the site of fragmentation, and they may be lost if their habitat sites are areas where fragmentation routinely occurs [6], [7].

Crowding effects

Immediately following habitat fragmentation, crowding effects may be observed in patches immediately surrounding the fragmentation barriers.  This can be attributed to mobile species that had their habitat destroyed in the fragmentation process relocating to the newly formed patches.  Crowding and overpopulation are synonymous, and with overpopulation comes competition for limited resources.  If two or more species are trying to occupy a similar ecological niche (such as a certain type of nesting ground, or preying on an identical food source), and there are limited resources, one species will most likely out-compete another, which may lead to loss of species in that area.

Invasive species

Invasive species are exactly what their name implies, a foreign species that colonize a habitat that are non-native to them.  Invasive species can cause threats to biodiversity by invading a habitat and competing with native species for resources.  Invasive species may have a greater chance to thrive in the habitat they invade because of the predator release hypothesis, which basically states that an invasive species may thrive in a new habitat because it isn't burdened by being hunted by predators in its natural habitat.

Invasive species also tend to thrive in areas of intermediate levels of disturbance, which habitat fragmentation may offer [7].  The effectiveness of the invasive species can depend on many, many factors.  The actual shape of the fragments, as well as method of species' dispersal can play a role in helping invasive species colonize new areas [8].  This concept is illustrated in figure 3.

Figure 3:  How the landscape is fragmented affects invasive species dispersal.  Here we will look at species X, who needs 100 ft. squared to colonize a new area, and can only disperse ranges of 450 ft.

Key:

Scenario 1: A habitat is fragmented in large clumps with similar habitats.

Here species X can colonize all three patches, when it migrates from patch 1 to patch 2 to patch 3, as the distance between those three patches in that order do not exceed the species' dispersal range.  Also, all three habitats are large enough to accommodate the species X's area requirement.

Scenario 2: A habitat is fragmented with the same distance between patches, but patch 2 is much smaller in area.

In this scenario, species X cannot colonize either patch 2 or patch 3.  Patch 2 cannot be colonized because it is too small, while patch 3 cannot be colonized even though it is large enough because it is too far away from patch 1.

Figure 3 by Dan Anderson, with concept originating from K.A. With [8]

Edge effects

Edge effects are the effect the perimeter of a habitat have on the biota that live within.  Edge effects include physical characteristics, such as increased lighting, wind, noise, and chance of encounter with humans or livestock. [4]  These unnatural levels of disturbance can effect organisms in many ways, including small effects such as animal's hindered sense of tracking by scent due to increased wind, or large effects, such as increased likelihood in getting slaughtered by an edge-causing road.

Non-physical effects of edges also impact biodiversity such as changes in predator-prey relationships.  For example, the Cowbird seems to be attracted to habitat edges and likes to steal species' of birds nests for their own young [7].  Edges can attract different species of plants that are prone to compete for lighting.

Isolation effects

Isolation of habitats from one another can have profound effects on the biodiversity within.  If populations of a species are isolated from neighbors of the same species, there is increased likelihood of inbreeding, which leads to genetic depression, and an increased likelihood of diseases associated with inbreeding.  

Barrier effects

Barrier effects are the effects of habitat fragmentation that result in species not being able to travel.  This can affect things such as migration patterns between different seasons, or species that need to roam large areas to find food.  Barriers for aquatic species can drastically reduce populations if spawning locations are blocked off because of barriers such as dams [7].

Effects on humans

Yes that's right habitat fragmentation has an effect on humans too!  People seem to enjoy heterogeneity in their landscapes, which can leave them with a feeling of connectedness with nature coupled with a calming effect.  Stress reduction has been recorded in areas that are more natural.  Edges such as roads reduce mobility for pedestrians and barriers such as highways can cause community disruptions.  Those with restricted mobility (such as the physically disabled or blind) are most heavily impacted by fragmentation by roads. [9].