The theory of hotspot preservation follows from the conjecture, “How can we protect the most species per dollar invested?” (Myers 2000) as well as the conservationist desire to protect as much biodiversity as possible. Hotspots are generally considered to be areas which hold large reserves of biodiversity. However, there are various methods of defining and measuring biodiversity, and as such, there are various methodologies that can be used to determine hotspots. Hotspots can be defined in terms of endemic species concentration, threatened species concentration, species richness, and/or rate of habitat loss. This section of the solution outlines the leading methodologies for hotspot determination, presents an analyses of the outlined methods, and then states conclusions as to which methodologies we suggest be applied and how this should be done.
There are two main competing methods as to how hotspots should be determined (Myers 2000, Reid 1998). The first and most widely used method examines the species endemism and threat in a given area. Another method, which seems to be more used on smaller scales, examines the species richness in a given area. Other methods, which examine factors such as rarity, number of threatened species1and surrogate measures (Reid 1998), do exist but have not been widely applied.
The method that has been most widely applied – and is currently being used by organizations like Conservation International (Conservation International 2007) – defines hotspots based on the concentration of endemic species in a region and the level of threat faced by the region (Myers 2000). This method was proposed by a group of scientists led by Normal Myers. His methodology defined as the following:
1.“To qualify as a hotspot, an area must contain at least 0.5% or 1,500 of the world's 300,000 plant species as endemics.”
2.“A second determinant of hotspot status, applied only after an area has met the 'plants' criterion, is the degree of threat through habitat loss. To qualify, a hotspot should have lost 70% or more of its primary vegetation, this being in the form of habitat that usually contains the most species, especially endemics.”
Vascular plants were chosen as the metric for endemism because they are “essential to virtually all forms of animal life and are fairly well known scientifically” (Myers 2000). Myers’ data also included statistics from four vertebrate groups (excepting fishes because of the limited knowledge on aquatic species). However, this data was not used to actually determine hotspots – it was included as back-up support and as a basis for other comparisons. Invertebrate species were not integrated into the methodology due to the scarcity of knowledge on the topic. Myers acknowledged their importance, but said that this issue is reasonably addressed through the correlation between the concentration of endemic invertebrate species and the concentrations of the other measured endemic species. The data in the study was collected from a large pool of international scientists and extensive professional literature (Myers 2000).
The boundaries of the hotspots were determined by examining biological commonalities. Myers wrote, “Each of the areas features a separate biota or community of species that fits together as a biogeographic unit”.
Using the criteria outlined above, Myers defined 25 biodiversity hotspots globally. Myers’ study, published in 2000, has since been updated to modify hotspot boundaries and locations based on current and updated data (Conservation International 2007). The updated list can be found at http://www.biodiversityhotspots.org/xp/hotspots/Pages/default.aspx.
While Myers designed his methodology for terrestrial use, it has also been adapted and applied to marine ecosystems2 (Roberts 2002). Details of this modified methodology and the resulting marine hotspots can be found in Roberts’ article “Marine Biodiversity Hotspots and Conservation Priorities for Tropical Reefs”, published in 2002.
Another approach to hotspot delineation defines hotspots as the regions with the highest levels of species richness. This method uses various approaches to measure richness and rank importance using this metric. It does not seem that this method has been prominently applied to a global scale, though it has been used in specific regions and for specific taxa. Prendergast conducted a study in the United Kingdom in which he defined “hotspots as the top 5% of record-containing 10-km squares (ranked by number of species per square)”. Reid also mentioned an application of the species richness method by the United States “to identify gaps in the existing network of protected areas.”
There is no analog to the widely used Myers method for endemism and threat for species richness. Overall, it is less developed, and its applications have been less uniform. This conclusion stems from the lack of extended research on this method and its uses.
Hotspots determined separately using species richness, endemism, and threatened species methods do not exhibit strong congruence – that is, the hotspots determined by each method largely do not lie in the same areas. (Orme 2005, Reid 1998). Orme conducted a study examining hotspots for avian species and found very minimal congruence between the three categories. He wrote, “Cumulatively the three sets of hotspots occupied 1,275 grid cells, of which only 2.5% (32 grid cells) were common to all types…Rather than being congruent across hotspot types, 82.4% (1,051) of hotspot grid cells were idiosyncratic to individual types, with the remaining 15.1% (192) of hotspot grid cells being shared between pairs of hotspot type.” Essentially, most of the hotspots that were determined arose from only one methodology. A moderate number of hotspots arose from some combination of two methodologies, but very few arose from all three methodologies.
These results suggest that the choice of hotspot methodology is not trivial, as different methodologies would define different conservation priorities. Because of this, an examination of utility is also needed to determine which method will define hotspots that will be most useful for conservation purposes.
To examine utility (or the usefulness of a given methodology), it is useful to survey which hotspots have high values for both determining and non-determining criteria. Orme’s study of avian hotspots found that “the endemism hotspots actually contained a greater proportion of overall species richness than did the species richness hotspots and a greater proportion of threatened species than did the threat hotspots”, while the converse of this statement did not prove to be true for both species richness hotspots and threat hotspots.
Because hotspots determined by endemism also encompass relatively large amounts of species richness and threatened species, they might be inherently more useful than the hotspots determined by the other methodologies. However, there is still a danger of losing some of the variety in biodiversity (perhaps corresponding to richness and threatened species) if other methods are not considered. Orme summarized, “This scenario provides some support for the use of endemism as a criterion for identifying hotspots, but more our results indicate the need to use multiple indices of diversity in identifying areas of high conservation priority”.
The Myers method of hotspot determination through endemism and threat is the most well developed and extensively applied (it has been applied on the international scale both terrestrially and aquatically) of the leading determination methods. It also seems to be a relatively reliable way of choosing hotspots that encompass many facets of biodiversity. Furthermore, it seems that the results from this method are already being considered in the conservation methods of some organizations. From these reasons, it follows that the endemism/threat approach should be used as the primary method for determining hotspots.
By preserving areas high in endemism and threat level, species that cannot and do not thrive elsewhere are protected. If their habitats are destroyed, then they will disappear forever – indeed, it is their endemism that rends them crucial. By contrast, non-endemic species can still thrive even if one of their habitats is destroyed as they have other native ranges. Also, as many non-endemic species are also present in the same regions as endemic species, they will be conserved as endemic species habitats are conserved.
However, this suggestion does not mean that endemism and threat are the only factors that should be considered during hotspot determination. Rather, the endemism/threat method will provide a good basis of hotspots that will cover a fair percentage of the Earth’s key biodiversity reserves. There will also key habitats that are rich in other metrics of biodiversity that should be added to the hotspot array as fit. These areas may include hotspots determined through methods that involve species richness and threatened species, and may also take into account metrics like the Simpson and Shannon indices. Different methodologies and/or existing research can be used to determine where such areas lie.
The actual delineation of specific hotspots should be based on the significant research that has already been done in this subject, and through the updated application of these methods to a changing world. After hotspots are determined, they should be targeted by conservation efforts as they provide a way of preserving many species with minimal funds and effort. The status of hotspots should be periodically re-examined examined, in accordance with guidelines set by the International Committee on Biodiversity, to ensure the continued relevance of already existing hotspots and perhaps incorporate crucial areas that were missed in the initial determination.