THREATS TO BIOLOGICAL DIVERSITY 1 HABITAT LOSS AND

THREATS TO BIOLOGICAL DIVERSITY 1: HABITAT LOSS AND FRAGMENTATION Lecturer: James Reeler Material by: Sam Hopkins

WHAT IS HABITAT LOSS AND FRAGMENTATION ? q Habitat loss is when a habitat is changed from one type to another q Habitat fragmentation is where habitats are divided into smaller parts

WHY IS IT SO IMPORTANT ? q Habitat loss reduces the amount of habitat available q Thought to be the most important threat to biodiversity at the moment q Fragmentation results in the pieces of habitat increasing in insularity with larger edges as well as a loss of total habitat

WHAT CAUSES HABITAT LOSS AND FRAGMENTATION q Habitat loss and fragmentation are caused primarily by humans q For example q Building q Draining wetlands q Nutrient enrichment q Grazing q Cultivation q Dredging q Stopping fire q Clearing

EDGE EFFECTS 1 q As the habitat becomes fragmented the edge of the forest increases q The edges are different to the interior of the fragment in climate, soil environment and species composition q Each fragment of habitat is surrounded by a “matrix” which is the term used for the modified habitat

EDGE EFFECTS 1 q The species at the edge of the habitat tend to differ from the ones in the centre of the fragment q This is seen in the vegetation present in forest fragments where q Stem density increases at the edge q Species richness increases q Shade intolerant species grow at the edge q Shade tolerant species stay in the centre q Tree mortality at patch edge

EDGE EFFECTS – HERPATOFAUNA OF MADAGASCAR 2 q On Madagascar 90% of the forests have been lost q The remaining forests persist as small isolated fragments q This increases the numbers of edges q It is suggested that these edges will affect the herpatofauna as they have quite specific physiological needs

EDGE EFFECTS – HERPATOFAUNA OF MADAGASCAR 2 q In one study the edge effects were found to influence the distribution of many species q The study was conducted in patches of rainforest with anthropogenic scrub in between q Some species only inhabited the interior of the forest q Some species preferred the edge of the forest q It was found that the season affected certain species affinity for the edge or interior

EDGE EFFECTS – HERPATOFAUNA OF MADAGASCAR 2 q Edge avoiders q q Interior avoiding q q Mantidactylus bicalcaratus Omnipresent q q Mabuya elegans Seasonal q q Mantidactylus boulengeri Hemidactylus mercatorius Edge avoiding reptiles and amphibians are more prone to extinction

ISLAND BIOGEOGRAPHY 3 q As each fragment of habitat is surrounded by an altered habitat it is possible to look at these fragments as islands q A lot of theory on island communities is relevant to habitat fragments q The risk of local extinction in single fragments becomes higher as the fragment is often too small to support a viable population q Re-colonisation from other fragments is possible however this depends upon the distance of the nearest fragment

ISLAND BIOGEOGRAPHY 3 q A number of studies have looked at the island effect on mammals, birds and lizards in Western Australia q There are 23 preserves varying in size from 34 – 5119 hectares q The birds did not seem to be affected by this fragmentation, possibly due to their ability to re-colonise areas using shrubby growth and tree lined roads q The lizards and mammals were affected by the isolation as if their were on an oceanic island q Some of the lizards and bird had already become extinct in some of the preserves

HABITAT DESTRUCTION CAUSES SPECIES TO DECLINE – ANURAN SPECIES IN ONTARIO CANADA 5 q 70% of wetlands in southern Ontario have been destroyed q Much of this land is now used for agriculture q In a study on the anurans in the area, anuran diversity as well as density decreased in agricultural areas as well as land down stream from the agriculture q This was seen for 7 species of frog

FRAGMENTATION CAUSES SPECIES TO DECLINE – THE MICRO FROG q The micro frog (Microbatrachella capensis) now on the IUCN red data list as critically endangered 6 is q This has been caused by habitat destruction q The habitat the frog relies on is sand plain fynbos, it is unique in its composition of acidophilic plants such as ericas and proteas 7

FRAGMENTATION CAUSES SPECIES TO DECLINE – THE MICRO FROG q Over half of the sand plains fynbos on which the micro frog relies is under human settlement and only 0. 013% of the fynbos type remains 7 q One of the few remaining sites is in centre of Kenilworth race course q It has only lasted here because of the protection that the racecourse has provided q As you can see from the photo it is surrounded by human settlement q The area is only 56 hectares

SOME SPECIES BENEFIT q Where habitat is destroyed or fragmented animals benefit q q Rats q Foxes q Canadian Geese q Pigeons q European sparrows q q Grey squirrels House mice These species are often thought of as pests some

SO WHAT CAN WE DO ? q A controversial concept is to have corridors between fragments to allow the movement of species q The idea behind a corridor is that a strip of natural habitat is allowed to remain in the unnatural matrix q It should link two fragments of habitat that are being conserved q This is meant to allow for local extinctions and re-colonisation q In practice it is not so simple

CONSERVATION CORRIDORS q There arguments and studies supporting and refuting the use of corridors q For a look at a conservation corridor plan in Minnesota go to www. de-chant. com/tim/nhc/index

FOR CONSERVATION CORRIDORS q Fahrig and Merriam (1985) 8 tested a model that compared the age structure and population size of patches of habitat that were linked or not q They then applied the model to the white footed mouse (Peromyscus leucopus) q The white footed mouse lives in patchy forests and doesn’t like open areas q They applied the model to populations of mice that were isolated or linked to another population by a corridor q They found that isolated populations had a lower growth rate

FOR CONSERVATION CORRIDORS q A study by Aars and Ims (1999) 9 focused on voles q They looked at population sizes and the genetics of the population q The voles had the same population size with or without the corridor q The corridor enhanced the movement of female voles from one population to the other q The corridor did not affect the movement of males from one population to the other q This small increase in movement by the female voles could enhance genetic diversity within the fragmented populations

AGAINST CONSERVATION CORRIDORS q An overview by Mann and Plummer (1993) 10 discussed the use of habitat corridors q The report was written after a conference where only 5 out of the 36 papers presented empirical data and three of them showed that animals rarely move along them q The problems with corridors are: q Fire q Disease q Introduced species q Costs

ACROSS BORDER PARKS 11 q The largest example of an across border (transfrontier) park is in Southern Africa q It is an agreement with Kruger in South Africa, Limpopo in Mozambique and Gonarezhou in Zimbabwe q The area includes 4 main habitat types and boasts species numbers of at least 147 mammals, 116 reptiles, 49 fish, 34 frogs, 500 birds and 2000 plants q It is about 40, 000 square km q Aims to allow more natural migration patterns by taking down fences

REFERENCES 1. Freidenburg, L. (1997) Physical effects of habitat fragmentation in Fielder, P. and Kareiva, P. Conservation Biology for the coming decade pp 66 -79 2. Lehtinen, R. M. et al. (2003). Edge effects and extinction proneness in a herpatofauna from Madagascar. Biodiversity and conservation 12: 1357 -1370 3. Cox, G. W. (1997) Conservation biology. Pp 123 - 131 4. Debinski and Holt (2000) A survey and overview of habitat fragmentation experiments. Conservation Biology 14: 342355 5. Bishop, C. et al. (1999) Anuran development, density and diversity in relation to agricultural activity in the Holland river watershed, Ontario, Canada (1990 - 1992). Environmental monitoring and assessment 57: 21 -43 6. De Villiers, A. L. (2004). Microbatrachella capensis (Boulenger, 1910). In Atlas and red data book of the frogs of South Africa, Lesotho and Swaziland. Eds Minter, L. R. , Burger, M. , Harrison, J. A. , Braack, H. H. , Bishop, P. J. and Kloepfer, D. pp 241 -244 7. Mc. Dowell, C. (1989). Conservation and horse racing: the unseen connection. Veld and Flora 75: 36 -39 8. Fahrig and Merriam (1985) Habitat patch connectivity and population survival. Ecology 66: 1762 - 1768 9. Aars and Ims (1999) The effect of habitat corridors on rates of transfer and interbreeding between vole demes. Ecology 80: 1648 - 1655 10. Mann and Plummer (1993) The high cost of biodiversity. Science 260: 1868 - 1871 11. www. environment. gov. za/projprog/tfcas/gltp