The University of Southampton

Tag: fragmentation

Fragmentation devastation: Why terrestrial habitats around the globe are being pushed over the edge.

Posted on by Dmitri Dharmasena

Habitat fragmentation is a term describing the process by which a large  habitat is broken up into numerous smaller habitats of decreased area and size, separated by a matrix of new unfamiliar habitat types – driven by the action of habitat loss (Didham, R.K., 2010). The loss of habitat through fragmentation is thought to be one of the main drivers of global biodiversity loss and can be either naturally occurring (climate change, volcanism, fires etc.) or human induced.

 

“70% of remaining forest is within 1km of the forest edge..” (Haddad et al, 2015)

 

Figure 1: The process of habitat fragmentation shown over time. Black regions represent areas of habitat and white regions represent newly formed matrix habitats. (Source: Fahrig, 2003).
Figure 1: The process of habitat fragmentation shown over time. Black regions represent areas of habitat and white regions represent newly formed matrix habitats. (Source: Fahrig, 2003).

 

What are the major effects of habitat fragmentation?

A long term global forest fragmentation study revealed that decreases in fragment area and an increase in fragment isolation, generally causes a drop in the abundance of:

  • Mammals
  • Birds
  • Insects
  • Plants

In tropical forests, reduced fragment sizes led to an increase in the portion of edge habitat exposed to unfamiliar surroundings. Following the increase in edge habitat, a shift in the physical environment was observed which caused a subsequent loss in the oldest and largest trees from these fragments, which had knock-on impacts on the wider community and specifically insect community compositions (Haddad et al, 2015).

Figure 2: Fragmented forests in the tropics.
Figure 2: Forest fragmentation in the tropics (Source: ALERT, 2015).

Fragmentation also effects communities through alterations of predator-prey interactions. It has been theorised that specialist predators are affected more severely by the fragmentation than their prey leading to a lower specialist predator abundance (Ryall & Fahrig, 2006). Generalist predators whom live predominantly within the matrix are thought to be benefited by increased fragmentation, so long as the new matrix is able to provide the generalist predator with alternative resources (Ryall & Fahrig, 2006). These adjustments will have cascading effects down through communities due to a rise or fall in the populations of top predators and their prey.

 

What is being done to help?

Case study: The Bhutanese Tiger corridor

One mechanism that has been implemented around the world is the use of ‘wildlife corridors’ (Silveira et al, 2015), which serve to reconnect fragmented patches of habitat. The Bhutanese Tiger corridor, from Northern India into Bhutan (see figure 2) has proven that this method does work. The corridor connects isolated Tiger habitats that now allow free passage for Tigers and other community species across a far greater space of land. Since its introduction the Bhutanese Tiger population has risen by more than a third of its previous population estimate.

Figure 2: A map visualising the Tiger corridor implemented between North Eastern India and Bhutan.
Figure 3: A map visualising the Tiger corridor implemented between North Eastern India and Bhutan (Source: Broad, 2012).

 

Fragmentation induces diverse changes that progressively filter through ecosystems. It  considerably lowers species richness of both plants and animals and in many cases it has impacted the structure and make up of entire animal communities. Habitat fragmentation is therefore an extreme threat to virtually all terrestrial biodiversity. Consequently, conservation efforts and habitat restoration projects must being immediately in order to prevent catastrophic losses and extinctions of some of the most iconic species on earth.

 

[Word count: 499]

 

 

References

  • ALERT, (2017). Forest fragmentation in the tropics.. [image] Available at: http://alert-conservation.org [Accessed 21 Mar. 2017].
  • Broad, M. (2012). NE Indian Tiger corridor. [image] Available at: http://pictures-of-cats.org/the-tigers-of-bhutan.html [Accessed 20 Mar. 2017].
  • Didham, R.K., 2010. Ecological consequences of habitat fragmentation. eLS.
  • Fahrig, L., 2003. Effects of habitat fragmentation on biodiversity. Annual review of ecology, evolution, and systematics, 34(1), pp.487-515.
  • Haddad, N.M., Brudvig, L.A., Clobert, J., Davies, K.F., Gonzalez, A., Holt, R.D., Lovejoy, T.E., Sexton, J.O., Austin, M.P., Collins, C.D. and Cook, W.M., 2015. Habitat fragmentation and its lasting impact on Earth’s ecosystems. Science Advances, 1(2).
  • Ryall, K.L. and Fahrig, L., 2006. Response of predators to loss and fragmentation of prey habitat: a review of theory. Ecology, 87(5), pp.1086-1093.
  • Silveira, L., Sollmann, R., Jácomo, A.T., Diniz Filho, J.A. and Tôrres, N.M., 2014. The potential for large-scale wildlife corridors between protected areas in Brazil using the jaguar as a model species. Landscape ecology, 29(7), pp.1213-1223.

 



Roads Reduce Role of Rainforests

Posted on by Anonymous

Rainforests are considered ‘the finest celebration of nature ever known on the planet’ yet increasing pressure to develop new roads for economic growth is their biggest threat.

Tropical rainforests cover 2-7% of Earth. They support 170,000 plant species. Their small area but tremendous biodiversity makes them global hotspots for conservation funds.

High levels of rainfall and constantly high temperatures creates a unique habitat. Many trees packed closely together creates a closed canopy. As a result, the rainforest is dark and humid. There is lower light, wind and temperatures as a result that species need to be specially adapted to in order to thrive (Laurance et al. 2009).

New developments threaten this structure. Species can either respond and adapt to new conditions or face the risk of extinction.

Rainforests are especially vulnerable to economic pressures. Roughly 2.5 million hectares (25,000km2) of the Brazilian Amazon are lost every year through deforestation. Economic growth is often the main driver for habitat loss. If the current rates continue, within 50 years, global rainforests are likely to be lost forever.

Many activities lead to deforestation but roads are seen as especially detrimental (Figure 1). Opportunities for logging, oil and mining often drive the development of new roads (Goosem 2007). Previously untouched areas are now accessible via roads and are now vulnerable to widespread biodiversity loss (Brudvig et al. 2015; Haddad et al. 2015).

Figure 1. New roads create barriers between previously connected species. Barriers for reproduction and pollination ultimately lead to species loss.
Figure 1. New roads create barriers between previously connected species. Barriers for reproduction and pollination ultimately lead to species loss.

The issue is not only minor access roads but large highways built for an increasingly urban world. The Trans-Amazonian Highway in Brazil is 4000km. This only makes it the third longest highway in Brazil (Figure 2).

Destruction of the rainforest is therefore a primary cause of plant biodiversity loss. Roads will change rainforest habitats from large and pristine to small and isolated. New edges are created alongside roads. Species are impacted more than this than widespread deforestation. This process of habitat fragmentation creates smaller, isolated populations and plant species are lost (Linert 2004; Gossem et al. 2011; Weiner et al. 2014).

Figure 2. Trans-Amazonian Highway is among one of many road developments through tropical rainforests that result in widespread deforestation and loss of important plant species that play vital roles in regulating carbon dioxide levels on Earth.
Figure 2. Trans-Amazonian Highway is among one of many road developments through tropical rainforests that result in widespread deforestation and loss of important plant species that play vital roles in regulating carbon dioxide levels on Earth.

Overall, trees lost from the rainforest allows light to reach the ground that was not able to before. Shade preferring species are no longer the best suited. Those plants that thrive on more light become more successful (Laurance et al. 2009). Species that were one dominant no longer are.

These changes to the surrounding environment impact important interacting species. Smaller patches with different conditions attract fewer plant species and therefore fewer pollinators. Pollinating species are likely to decline as a result, threatening their own survival and that of the plants (Aguilar et al. 2006).

If reproductive output declines, the number of species surviving to continue the population declines. The negative cycle continues until a whole species is extinct. Community structure is altered and important interactions are lost.

Each plant species, rare or common, plays an important role in regulating carbon, purifying water and stabilising soil qualities. Loss of species variety creates areas that are extremely similar. Soon, rainforests will lose their functional role and contribute less to the global system.

[496 words]

REFERENCES

Aguilar, R., Ashworth, L., Galetto, L. & Aizen, M. A. (2006) Plant reproductive susceptibility to habitat fragmentation: review and synthesis through a meta-analysis. Ecology Letters, 9, 968-980.

Brudvig, L. A., Damschen, E. I., Haddad, N. M., Levey, D. J. & Tewksbury, J. J. (2015) The influence of habitat fragmentation on multiple plant-animal interactions and plant reproduction. Ecology, 96, 2669-2678.

Cunningham, S. A. (2000) Effects of habitat fragmentation on the reproductive ecology of four plant species in mallee woodland. Conservation Biology, 14, 758-768.

Goosem, M. (2007) Fragmentation impacts caused by roads through rainforests. Current Science, 93, 1587-1595.

Haddad, N. M., Brudvig, L. A., Clobert, J., Davies, K. F., Gonzalez, A., Holt, R. D., Lovejoy, T. E., Sexton, J. O., Austin, M. P., Collins, C. D., Cook, W. M., Damschen, E. I., Ewers, R. M., Foster, B. L., Jenkins, C. N., King, A. J., Laurance, W. F., Levey, D. J., Margules, C. R., Melbourne, B. A., Nicholls, A. O., Orrock, J. L., Song, D. A. & Townshend, J. R. (2015) Habitat fragmentation and its lasting impact on Earth’s ecosystems. Sci. Adv.

Laurance, W. F., Goosem, M. & Laurance, S. G. W. (2009) Impacts of roads and linear clearings on tropical forests. TREE, 1149, 1-11.

Lienert, J. (2004) Habitat fragmentation effects on fitness of plant populations – a review. Journal for Nature Conservation, 12, 53-72.

Weiner, C. N., Werner, M., Linsenmair, K. E. & Bluthgen, N. (2014) Land-use impacts on plant-pollinator networks: interaction strength and specialisation predict pollinator declines. Ecology, 95, 466-474.