With the world being as degraded as it is, most of the worlds biota needs to be contained in a nature reserve. Which area to conserve is a difficult question and land is often picked for a number of reasons like the diversity of the species, the rarity of particular species and the naturalness of the area. The nature reserves also often serves a number of other functions and people can hunt or hike or there is some other way people can make money from them such as accommodation. (Image from www.bigfoto.com)
Once the area to be conserved has been decided upon, the actual size of the reserve is very important. Island biogeography supports the notion that large islands will support more species than small islands and a nature reserve can be considered an island in a sea of degraded land 2. Larger reserves will generally support a larger diversity of species and interactions. When looking at mammal extinction, the rate of extinction is related to park area with smaller parks having more extinctions. Large reserves allow the colonisation of species from other parts of the reserve even though having two smaller reserves would mean that if one of the reserves was destroyed the other would still contain the suite of species, a disaster like a fire or a flood would probably not destroy a whole large reserve and easily allow recolonisation from the undestroyed part. Many species have a minimum area requirement but it is not often heard that a species needs a maximum area requirement. The top carnivores like the wolves, bears and lions need large ranges and if the primary objective of nature reserves is to preserve the species present in the pristine environment then it follows that the reserves need to be large 6. Wanting the reserve to be a large area does not mean a large area of unwanted land, the area must be researched for its usefulness in conservation.
The Borro Colorado Island was made a reserve in 1923. It is a small area and has a number of birds that will not fly over the water that surrounds it. Of these species there are three ant following birds, the small spotted antbird (Hylophylax naeviodes), the medium bicolored antbird (Gymnopithys bicolor) and the large ocellated antbird (Phaenostictus mcleannani). These birds were tracked for 11 years from 1960 to 1971. The spotted antbird was stable though this period at 20 pairs per km 2 the bicolored antbird declined from 3 pairs per km 2 to 1.5 pairs per km2. The large ocellated antbird was nearly extinct by 1971. This is a pattern that has been seen with other birds on the island, since the area was made a reserve 45 species (22%) of the avifauna had gone by 1960. There is little explanation for this and the authors suggested that the small area does not allow escape of adverse conditions like a low rainfall year. (Images from www.mangroverde.com, www.canopytower.com, www.birdersview.com)
In the Amazon rainforest there is a problem in the nature reserves with guarding and defending the reserve from hunters, loggers, fishermen, miners and land clearing. The reserves that have been selected have been chosen on their biological merit being centres of endemism or diversity. No consideration has been given to their defensibility which would seem wrong when there are a number of people out to exploit the forest and a few guards with no authority, weapons and each defending an area the size of Delaware (6053km2). A large reserve that encompassed a whole watershed would allow the protection of the reserve at a single point where the large river leaves the reserve. The waterways are the main way that reserves are penetrated. This would also protect an entire watershed and all their aquatic resources, meaning less incidences of pollution and protection of spawning grounds. (Images from www.wendeeholtcamp.com, www.recycleworks.org)
There are however, studies in the scientific literature that suggest that a series of smaller reserves would be more useful in conservation. A study by Simberloff and Abele (1976) saw them cutting up large red mangrove islands into a smaller archipelago and then counting the numbers of species present after a number of years. They found that the resulting islands had more species overall although other islands may act as sources. This piece of work has been examined by a number of other scientists who suggest that making statements like this does more harm than good because it gives planners an excuse for making reserves smaller. It also does not take into account the type of species that are being counted. The case should never be 'which refuge contains more species' but instead 'which refuge contains more species that would be doomed to extinction' 5. (Images from www.floridaoceanographic.org, www.uaf.edu)
Erwin et al (1995) studied the water birds in some of the smaller Florida keys. Birds were found to prefer the medium of the smaller islands, the smallest islands were prone to washing over and the largest islands tended to have year round mammalian predators. An example is seen in white heron numbers (Ardea herodias). Their nest numbers are negatively correlated to island area suggesting that for water birds smaller is better. (images from www.islanderfloridakeys.com, www.ckphoto.com)
In a study by Boeklen in 1986 a computer simulation of genetic drift and allele fixation within populations was looked at. It showed that sub-divided populations with occasional migrations preserve more heterozygotes over a long period of time. Two divided populations will also preserve alleles longer than one population of the same number of individuals. Therefore, an archipelago of refuges with occasional migration seem to be optimum for genetic conservation.
It is all very well running models and predicting what size is necessary for a reserve to succeed but in practice it is not that easy. Land is not easy to obtain and maintain. In a study in Eastern North America the smallest area the terrestrial mammals need was calculated and then compared to the size of the reserves present. The terrestrial mammals need an area of 5037 km 2 and out of the 2355 reserves in the area only 11 were big enough. 14 of the reserves were greater than 2700 km2, 8 were greater than 5037 km2 and only 3 were greater than 13,296 km2.
The shape of the reserve is also important. Each reserve will have an edge that abuts the degraded matrix. Many animals are affected by this edge and the edge is different for different species, some reserves for some species may be all edge. The park perimeter to park area ratio need to be taken into account. Smaller reserves will have a larger edge to area ratio. An irregularly shaped reserve will give a larger reserve edge and a smaller interior, this will promote edge species and cause interior species to decline. If there is a particularly heavily used road present within the reserve it can act as another edge. (Images from www.mongabay.org, www.umkc.edu)
Often reserve planners need to find a compromise between a number of different factors. A computer program may aid in making informed and non-biased decisions. Indexing, scores all of the potential reserves or reserve designs against defined criteria. Iterative techniques are used to assemble combinations of reserves that meet all of the criteria, for example, the combination of reserves must represent all of the endangered species in the area. Integer planning is a mathematical programming technique but tends to only use one criteria at a time and this is not realistic when looking at reserve design.
An example of the use of computer programmes to select areas for reserves is seen in a paper by Rothley (1999). In Nova Scotia there are already two national parks and five more forest nature reserves are wanted to complement them. The combinations of reserves are studied using three criteria, connectedness, total area and the number of rare plant species. The MOP screens the reserve designs in respect of the criteria giving a reduced number of reserve design alternatives and states if they are optimal for one of the three criteria or intermediate trade offs between the three. SMART is then used to find the best reserve design by ranking the designs on a scale for connectedness, total area and number of rare plants. In Nova Scotia 36 reserve alternatives were suggested three being optimal with respect to one of the three criteria and the other 33 being optimal compromise solutions. These designs are then ranked using SMART where the optimal design will be found.
The use of umbrella taxon to find suitable areas of land to preserve. Umbrella species are often a species with large area requirements. For example it is estimated that to protect a viable elephant population 1000 miles2 of land is needed. In conserving this land many other species may benefit however this land may not be ideal for the conservation of other species. No single taxon will be completely effective as a reserve selector. In a study by Ryti in San Diego, just looking at one taxon at a time, to preserve all of the bird species two of the canyons would need to be conserved, but to conserve all of the plant species 10 canyons need to be preserved. This suggests that plants would be the better umbrella taxon as they will conserve a larger area.
A biodiversity hotspot is an area of land with an increased species richness, high numbers of endemic species and high numbers of rare species. This is a way of assessing priorities for conservation as the amount needed to conserve is far larger than the amount available. In an article by Myers et al. the term hotspot was defined as areas containing large concentrations of endemic species There are at present 25 of these hotspots throughout the world and 15 of these occur in tropical forest. The idea is that these contain at least 0.5%of the worlds pant species as endemics Out of the 25 hotspots 15 of them contain at least 2,500 endemic plants and 10 of them contain at least 5,000 endemic plant species, also the area must have lost 70% of its primary vegetation. This initiative is being backed by Conservation International who have started up a critical ecosystem partnership with a $75 million investment. One of these hotspots is the Cape Floristic region. Image from news.bbc.co.uk/1/hi/sci/tech/3707888.stm)
The Cape Floristic region is an area of land 87,892 km2. In this area 70% of the plant species are endemic. This is also an important area for birds, mammals and other vertebrates. 10.1% of the area is already in reserves but this is mainly in mountainous areas that are not good for farming. Cowling et al. suggest another 40,000 km2 must be protected in some way. This figure takes into account representativeness and persistence, so the protected area will encompass many of the endemic plant species and in enough numbers that they will be able to survive into the future. However as always there is not enough money to carry out the plan and all the time more and more is being lost. (Images from www.biodiversityscience.org, www.eeb.unconn.edu, www.safloweressences.co.za, www.advance.ucon.edu)
The hotspot plan is not ideal and has a number of critics. Firstly the biodiversity hotspot for one species will not be the same for another and high species richness does not all ways follow high endemicity. Hotspots may miss species that are essential to conservation
I have already gone over the use of wildlife corridors in chapter 2. Here I will just recap. Wildlife corridors are a suggested solution to the problems of small reserve size and the lack of migration between populations. The corridor is meant to be a strip of natural habitat that is preserved in the unnatural land. This link between the two reserves is meant to allow for re-colonisation and gene flow between the two populations. I would like to go over the arguments for and against the use of wildlife corridors as it is not conclusive that they work. (Images taken from wildlifestewards.4h.oregonstate.edu/wildlife)
Fahrig and Merriam (1985) found populations of the white footed mouse (Peromyscus leucopus) that were linked to others had a higher growth rate and Aars and Ims (1999) found that having a corridor enhanced the movement of female voles enhancing genetic diversity. This follows on from Boeklen 1986 talking about stalling genetic drift and keeping heterozygosity in two populations connected. (Image from cedarcreek.umn.edu/mammals/cricetidae, www.ru.nl)
However in a review by Mann and Plummer (1993) they suggested a number of problems with the concept even if they do work, these were the easy passage of fire, disease, alien species and the cost of these corridors that are not proven to work. Images from crawfishcoofcentralflanc.com, www.honesthypocrite.blogspot.com, www.critterhut.com, www.freephoto.com)
It is not disputed that biodiversity should be conserved but how to conserve it is debatable. What to conserve along with how best to conserve it are issues discussed in the scientific literature all the time. Reserve design is part of this problem as different designs meet different conservation needs.
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