Habitat Fragmentation

HABITAT FRAGMENTATION

The essence of habitat fragmentation lies on our genuine understanding of the value of BIODIVERSITY. Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet (Wikipedia). Biodiversity is a measure of the health of ecosystems. Biodiversity is measured in terms of species richness, population abundance and distribution, and genetic diversity. Our concern on biodiversity and our interest on habitat fragmentation meet on our CONSERAVATION goals. Given our conservation goals, we want to establish the effects of habitat fragmentation on biodiversity.

Biodiversity is indirectly measured by habitat loss. What is habitat? How do we determine that a habitat has been lost?

Habitat is more than the landscape or the area. It constitutes the resources and conditions present in an area that produce occupancy, including survival and reproduction, by a given organism (Krausman, nd). In a previous blog entry, we have exemplified the Monfort bat cave as the habitat of fruit bats. This habitat offers refuge for the bats to sleep, be protected and able to reproduce, including easy access to foraging sites.

A habitat is lost once an area is no longer able to provide the resources and conditions which enable organisms to thrive in it. It is determined quantitatively when population growth rate of species decrease, when trophic chain lengths are reduced, when species interactions are altered, as well as when breeding success, dispersal success, predation rate, foraging success rate are reduced. This, generally, is the concept of HABITAT LOSS. Habitat loss is erroneously equated with HABITAT FRAGMENTATION. Farig (2003) clarified that HABITAT LOSS occurs with fragmentation while fragmentation may occur with no habitat loss.
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What then is HABITAT FRAGMENTATION? Several studies, specially those richly discussed by Farig, give different definitions of habitat fragmentation.
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HABITAT FRAGMENTATION occurs when a large expanse of habitat is transformed into a number of smaller patches of smaller total area, isolated from each other by a matrix of habitats unlike the original (Fahrig, 2003). Imagine New York City, particularly its skyscrapers and the well-known Central Park. Suppose the island of New York, prior to the construction of skyscrapers, is composed of the flora and fauna found in central park. After sometime, because of advances in both technology and demands of human existence, Americans started to occupy lots in New York City by cutting down trees. This is habitat fragmentation in the landscape level. The habitat of the entire island has been reduced to patches, and the matrix would be composed of skyscrapers.
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According to Franklin (2002) HABITAT FRAGMENTATION is the disruption of once large continuous blocks of habitat into less continuous habitat. It is the breaking up of a large intact area of a single vegetation type into smaller intact units (called patches). A habitat is measured in terms of configuration (size, shape) and habitat amount (or lack of habitat). And when this habitat undergoes fragmentation, the degree of fragmentation is measured in terms of patch size (which researchers report as ambiguous), patch isolation and reduction in habitat (simply habitat amount).
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The effect of habitat LOSS to biodiversity is crystal clear. When habitat is lost, biodiversity is also lost. However, the question on the effect of habitat fragmentation on biodiversity is not clearly established.
Habitat fragmentation has the following effects (not directly to biodiversity): (1) reduction in habitat amount, (2) increase in number of habitat patches, (3) decrease in sizes of habitat patches and (4) increase in isolation of patches.
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Reduction of habitat is almost similar to loss of habitat. A 10 hectare land habitat when disturbed by human activities such as 2 hectare subdivision, habitat worth 20% of the previously established is lost.
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The last three referring to patches actually have impact on the change in habitat configuration, although, careful analysis projects that these are also related to habitat reduction. One thing is for sure though, habitat loss and habitat fragmentation both result in smaller patches. PATCH ISOLATION is measured in terms its distance to the next nearest patch.
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Given these four effects of habitat fragmentation, we can establish the effects of habitat fragmentation on biodiversity. Habitat fragmentation is quantized by measuring a range of variables including abundance, density, distribution, reproduction, movement and species richness. Research findings show that birds had lower reproductive rates in small patches than in large patches. Also, fragmentation leads to a larger number of smaller patches. Smaller number of patches means more edges(this is analogous to surface area). Along the edges, there might be increased predation.

On the positive side, a research found a positive effect of fragmentation on butterfly species richness. Within this patches, preys may find isolation that would protect them from predators. This is a venue for them to increase their number. Coexistence of two competing species could also be extended by dividing the habitat (effect of fragmentation) into smaller patches.

What is more interesting also is that habitat fragmentation should be considered in terms of species. A 10 meter wide road constructed in the middle of a rainforest might be harmful or detrimental for insects in terms of their reproduction, survival and food sources but not necessarily for the Philippine eagle.

Our knowledge on the effect of habitat fragmentation will affect on how we design a sustainable working system that would balance with the natural demands of nature. We cannot expect man avoid constructing shelters in faithful consideration of habitat fragmentation. Fragmentation may be allowed considering its weighed advantages and disadvantages. Habitat fragmentation is an indicator for man to know when enough is enough.