Conservación

 

Biodiversity conservation in Costa Rica: a correspondence analysis between identified biodiversity hotspots (Araceae, Arecaceae, Bromeliaceae, and Scarabaeinae) and conservation priority life zones

 

Conservación de la biodiversidad en Costa Rica: análisis de la correspondencia entre áreas identificadas clave por su biodiversidad (Araceae, Arecaceae, Bromeliaceae y Scarabaeinae) y zonas de vida prioritarias para la conservación

 

Bert Kohlmann¹*, David Roderus², Ortwin Elle², Ángel Solís³, Xinia Soto⁴ and Ricardo Russo¹

 

¹ Universidad EARTH, Apartado postal 4442–1000, San José, Costa Rica.

² Abteilung Biogeographie, Am Wissenschaftspark 25–27, Universität Trier, 54296 Trier, Germany.

³ Instituto Nacional de Biodiversidad, Apartado postal 22–3100, Santo Domingo de Heredia, Costa Rica.

⁴ GIS Consultant, Apartado postal 580–2070, Sabanilla de Montes de Oca, Costa Rica.

 

*Correspondent:
bkohlman@earth.ac.cr

 

Recibido: 20 enero 2009
Aceptado: 12 octubre 2009

 

Abstract

This paper undertook an analysis of the distribution of high species richness and areas of endemism based on plants (Araceae, Arecaceae, and Bromeliaceae) and dung beetles (Scarabaeinae) inhabiting the different Holdridge Life Zones of Costa Rica. Using a geographic information system (GIS) we analyzed biogeographic provinces, in terms of their representativity in sampling areas, life zones, and protected areas. Species richness and endemism maps served as a base for conducting a gap analysis and defining 6 different levels of high priority conservation areas. What percentages of these priority areas are under some type of protection or conservation scheme and which of these areas should be enlarged were also investigated. The degree of feasibility that these areas under protection have for enlargement is indicated. A list is included of all the aforementioned registered species for Costa Rica, as well as their presence in the different Holdridge Life Zones and their endemism status. Four areas with the highest species richness were identified, and 3 new areas of endemism are proposed. The most important conservation priority areas are the tropical wet forests on the northeastern lowlands, the Osa Peninsula region, and the premontane wet forest along the Guanacaste, Tilarán and Central mountain ranges. This study clearly demonstrates the need to include and compare different groups of organisms in biodiversity–endemism studies, in order to obtain more robust and finer–grained studies.

Key words: high species richness areas, areas of endemism, life zones, representativity, Araceae, Arecaceae, Bromeliaceae, Scarabaeinae.

 

Resumen

El presente estudio analiza la distribución de áreas de alta riqueza específica y endemismos basado en plantas (Araceae, Arecaceae, y Bromeliaceae) y escarabajos del estiércol (Scarabaeinae), que habitan las diferentes Zonas de Vida de Holdridge en Costa Rica. Mediante el uso de un sistema de información geográfica (SIG) analizamos provincias biogeográficas, en relación a la representatividad de las áreas de muestreo, las zonas de vida y las áreas protegidas. Los mapas de alta riqueza específica y endemismo sirvieron de base para realizar un análisis de vacíos (gaps) y definir 6 niveles distintos de alta prioridad de áreas de conservación. También se investigó qué porcentaje de estas áreas prioritarias se encontraba bajo algún esquema de protección o conservación, y cuáles de estas áreas son susceptibles de ser ampliadas. Se indica igualmente el grado de factibilidad para que estas áreas crezcan. Incluimos una lista de todas las especies registradas para las familias antes mencionadas en Costa Rica, e indicamos su presencia en las diferentes Zonas de Vida de Holdridge, así como su condición de endemismo. Se identificaron 4 áreas de máxima riqueza específica y 3 áreas nuevas de alto endemismo. Las áreas prioritarias para la conservación identificadas fueron: (1), el bosque húmedo tropical de las tierras bajas del noreste; (2), la región de la península de Osa, y (3), el bosque húmedo premontano, a lo largo de las vertientes de las cordilleras de Guanacaste, Tilarán y Central. Este estudio demostró claramente la necesidad de incluir y comparar a diferentes grupos de organismos en estudios sobre patrones espaciales de biodiversidad–endemismo, con lo cual es posible obtener resultados más robustos y más detallados.

Palabras clave: áreas de alta riqueza específica, áreas de endemismo, zonas de vida, representatividad, Araceae, Arecaceae, Bromeliaceae, Scarabaeinae.

 

Introduction

Biodiversity conservation has become one of the most urgent tasks facing humanity because of the accelerating rates of biodiversity loss (Pimm et al., 1995). It is precisely (and perhaps perversely) that the most biodiverse areas and those with the highest levels of biodiversity loss are the least protected and with the greatest need for data regarding their species richness and levels of endemism (Pimm, 2000). An appropriate action toward this goal would be the establishment of global inventories, although the time required for both surveying and documenting this plethora of taxa far outreaches our present capacity. Availability of adequate data is also a limiting factor (Prendergast et al., 1999). Therefore, development of biogeographic atlases can be proposed as a practical tool for biodiversity conservation (Prendergast et al., 1993; Morrone, 2000) and hotspot identification (areas that combine a high biodiversity with a high threat degree by humans; Myers, 1988; Kappelle, 2008). A very important task of biogeography atlases is the study of diversity and endemism patterns in order to protect rare and endangered species. As Lomolino et al. (2006) indicate, 2 major tasks of this process consist of documenting the intensities and locations of hotspots for a particular taxonomic group and determining the degree to which different taxon–specific hotspots overlap spatially. Although levels of endemism and species richness are frequently positively correlated (Balmford and Long, 1995), unfortunately, many times such overlap does not exist (Bibby et al., 1992; Prendergast et al., 1993; Araujo, 2002; Cox and Moore, 2005; Lomolino et al., 2006). This fact compels the analysis of distribution patterns to be conducted region by region, in order to understand current scenarios and hence being able to identify biodiversity hotspots (Myers et al., 2000). As Gaston (2000) and Gaston and Spicer (2004) indicate, species are not uniformly distributed across the world and must therefore be mapped. Areas of high diversity usually elicit questions about their origins and possible conservation. However, other approaches such as the Method of Systematic Conservation Planning (Margules and Pressey 2000) is based on species rarity and complementarity rather than diversity hotspots.

The study and knowledge of the aforementioned situation in Costa Rica is of the utmost importance. Costa Rica belongs to one (Middle America) of the 36 world hotspots, as defined by Mittermeier et al. (2004). Costa Rica is a country with a small area (Fig. 1); it has 51 100 km² of continental and insular land surface, representing 0.03% of the Earth's surface (Jiménez, 1995; Ministerio del Ambiente y Energía, 2000). In the world's diversity ranking, Costa Rica occupies the 20^th place, approximately. As such, it is not considered a megadiverse country, since only 12 countries make up the list. However, what makes Costa Rica special is its species density (number of species per unit of area) (Valerio, 1999; Obando, 2002). Using this measure, Costa Rica's place in the world is highly recognized (Valerio, 1999, 2006; Obando, 2002, 2007). This country contains approximately 3.6% of the total expected world's diversity, and if the total number of described species is considered, this number jumps then to 4.5%, with more than 90 000 known species (66 946 insect species, 11 451 plant species, and 5 253 other invertebrate species; Obando 2007). To give a comparative idea of species density, Costa Rica has 234.8 plant species per 1 000 km², whereas Colombia, in second place, has only 43.8 plant species per 1 000 km² (Obando, 2007). Similarly, Costa Rica has 28.2 species of vertebrates (excluding fishes) per 1 000 km², whereas Ecuador, the second most biodiverse vertebrate country per km² in the world, has 9.2 species per 1 000 km², and the third most biodiverse vertebrate country, Malaysia, has only 4.4 vertebrate species per 1 000 km² (Valerio, 2006). This enormous biodiversity in Costa Rica is now under protection by a world–class national system of protected areas, which began in the 1970's and today protects almost 27% (governmental and private) of the national territory (Vaughan, 1994; Vaughan et al., 1998). Interestingly, Costa Rica is also the country with most ecotourists per km² worldwide, 22.47 international ecotourists/km² in the year 2007, with the African sub–Saharan countries as the next places with most ecotourists per km² (Kohlmann et al., 2008).

Costa Rica is considered to have a moderate proportion of endemics (Obando, 2007); approximately 1.3% of the known species are endemics. It is estimated that around 10% of the total plant species are endemics (1 102 species), whereas the different vertebrate groups vary from a minimum of 0.7% in birds to a maximum of 25% for the amphibians (Obando, 2007). Using these 2 groups (plants and vertebrates), 4 great areas of endemism have been identified for continental Costa Rica: the Central Volcanic Cordillera, the Talamanca Cordillera, the Central Pacific Region and the Osa Peninsula Region (Fig. 1); a fifth area has been identified on Cocos Island, in the Pacific Ocean (Elizondo et al., 1989). From the ecosystem point of view, the cloud forests are the most endemic ecosystems in the country (Obando, 2002), as the present study concludes too.

Adequate representation of biodiversity is ideally achieved by the use of multiple taxonomic groups (Stork and Samways, 1995; Halffter and Moreno, 2005; Pawar et al., 2007). However, due to time, funding, collection and taxonomic constraints for the majority of the groups, especially in tropical regions, many area–prioritization studies assume some similarity levels in species geographical distributions and consequently available groups are used as surrogates for others (Garson et al., 2002; Rondinini and Boitani, 2006; Pawar et al, 2007). Despite the popularity of the surrogacy approach, its efficacy remains unclear (Moore et al., 2003; Graham and Hijmans, 2006; Lamoreux et al., 2006).

This paper is an attempt at analyzing the distributional congruence of 4 different tropical taxonomic groups (Araceae, Arecaceae, Bromeliaceae and Scarabaeinae) and describing their overlap at a fine scale. A recurrent question is whether plant and vertebrate distribution patterns are reflected by those of invertebrates as well (Howard et al. 1988). Moritz et al. (2001) found high levels of congruence with data on tropical insects, snails, plants, and vertebrates only in areas with a clear history of geographical vicariance. In some other cases, like in tiger beetles, there seems to be congruence; in other cases the relationships are not clear (Mittermeier et al., 2004). The present study identifies biodiversity provinces indicating and analyzing the spatial correspondence of areas of high species richness and endemism for Costa Rica, using dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) and plants (Araceae, Arecaceae and Bromeliaceae).

Our analysis focused on continental Costa Rica; Cocos Island was not included because no Scarabaeinae material has been collected from that locality and only 1 species of Aphodiinae has been found to date. This analysis represents an effort to help define those areas most in need of conservation and sustainable use in Costa Rica. The study will also help define those areas that have been under sampled and therefore future collecting efforts can be directed. This study is also an expansion and continuation of a previous study which used dung beetles for a gap analysis (Kohlmann et al., 2007), considered a pioneer study in Costa Rica (Arias et al., 2008), because it represents the first attempt to use the actual distribution of all species belonging to a specific taxonomic group.

 

Materials and methods

Taxon information. Regarding the 3 plant families, Araceae, Arecaceae and Bromeliaceae, data on their distribution (geographic coordinates) were taken from the collections of the National Biodiversity Institute (INBio, www.inbio.ac.cr) and from the Missouri Botanical Garden electronic database (www.mobot.org), additional information was incorporated from Hammel et al. (2003). This information was further revised and updated by Drs. N. Zamora (Araceae and Arecaceae) and J. F. Morales (Bromeliaceae). The total number of plant species considered for this study is as follows (Appendices 1–(2)–3): Araceae, 229 species; Arecaceae, 107 species; Bromeliaceae, 187 species. No introduced species were considered for this study.

Information regarding Scarabaeidae beetle distribution was also taken from the collections of the National Biodiversity Institute. The Scarabaeinae (Coleoptera: Scarabaeidae) have been particularly well studied (Kohlmann et al., 2007). So far, 174 native taxa of Scarabaeinae have been reported from Costa Rica (Appendix 4).

Concluding, the 4 chosen groups have been particularly well sampled in Costa Rica, as well as systematically studied in great taxonomic detail; their analyzed distributional areas are relatively smaller than the study area, in accordance with Müller's (1981) 3 tenets for making these groups particularly well suited for the present biogeographic analysis. We are aware that the Araceae and Bromeliaceae tend to be hygrophilic by nature in Costa Rica, thus introducing some bias into the analysis, especially when discussing the drier northwest Pacific areas. However, this situation is balanced by the fact that the Arecaceae and the Scarabaeinae have radiated in humid, as well as in dry areas, and are therefore good representatives of the northwest Pacific.

Base vegetation map. One of the most popular systems used in Costa Rica and in 12 other countries in the region (Meza, 2001) for vegetation classification is the Life Zone System developed by Holdridge (1967). This system divides Costa Rica into 12 Life Zones and 11 Transition Zones (Fig. 2) based on environmental factors such as humidity, rainfall, and temperature. This system is thus independent of floristic relationships and the same zones can then appear in different regions of the world. According to Hall (1984), this system takes into account not only variations caused by latitude, but also by altitude, and is therefore especially useful for tropical mountainous countries (Meza, 2001).

The Life Zone System maps were directly taken from the Atlas Costa Rica 2000 (Instituto Tecnológico de Costa Rica, 2000) and were not modified for the present study. Sampling effort in this study is not proportional to polygon size, due to the fact that most of the sampling was done by INBio and this institution samples in national parks and other conservation areas with original vegetation cover and not in modified areas; therefore, one can argue that polygon size did not bias neither the collecting effort, nor the collecting site inclusion, which might have incorporated possible changes in original vegetation or ground cover.

According to this classification, the 5 most extensive vegetation types are: tropical wet forest (10.5% of the total country area), premontane wet forest (7.2%), lower montane wet forest (5.9%), premontane rain forest (5.6%) and tropical moist forest (5.5%) (Obando, 2002).

There are some limitations to this system. Besides total precipitation and temperature, the Holdridge Life Zone system can potentially vary along other environmental axes, such as the edaphic conditions, which could impact species abundance and endemism. For example, bioclimatic regions such as the Pacific dry forest consist of long belts along mountain/volcanic ranges, and by assuming that these long belts all share the same biodiversity category, there would be a risk of losing resolution when assigning conservation priority zones.

No standardized functional ecological classification exists for Costa Rica (Obando, 2007). Some incomplete attempts have been tried at establishing an ecoregion system, without success. Very recently (Sistema Nacional de Áreas de Conservación (SINAC), 2007 a) a new system based on phytogeographic units has started to be implemented in Costa Rica.

GIS Analysis. Some of the many advantages of using GIS techniques are the storage of large amounts of spatial information, the ease for mapping many map layers, and their use in modeling and predicting species distributions. For these reasons we have followed a GIS–oriented process for the elaboration of our biogeographic analysis.

GIS and data analyses were carried out by using ArcView ®3.1 (ESRI, 2002), ArcGIS®9.2 (ESRI, 2006) and Microsoft Excel® (2002) following the process outlined below:

1. – Assembling and cleaning of the database for each taxon (taxon names, type of endemism and location of collection sites). The great majority of the data came from the National Institute of Biodiversity (INBio), and as such is less than 20 years old and derives from protected conservation areas. The Missouri Botanical Garden data have similar characteristics. Data layers were generated using the collection sites for each species.

2. – Refinement and geo–referencing of geographic location data consisted of transformation to coverage format, correction of errors and inconsistencies such as redundant polygons, homogenization of geographic data bases, association of tables with the base map, addition of new collection points to original collection data bases, and elimination of redundant duplicate collection points. The layers containing the National System of Coordinates (Costa Rica Lambert North) were transformed to geographic coordinates (the same datum was always used: Fundamental de Ocotepeque, which is not compatible with generic geographical coordinate systems and requires specific parameters for its conversion). For distributional referencing (Appendices 1–(2,3)–4), each Holdridge Life Zone polygon was numbered (Fig. 2).

3. – For each taxon, the collection sites were superimposed on the Holdridge Life Zones obtaining the number of collection sites by taxa, as well as the total number of taxa, endemics and endemism type (endemics known to occur only in Costa Rica, shared with Panama, shared with Nicaragua, shared with Nicaragua and Panama, and total number for Costa Rica) for each life zone polygon.

For this study we found the use of the Holdridge system more amenable than distribution modeling for several reasons. First, the life zones of the Holdridge system have been well mapped, have been much used, and are very popular in Costa Rica, besides being considered very appropriate to the complexities of tropical vegetation (Gentry, 1978). It has also been widely used by the National Aeronautic and Space Administration (NASA) (http://gcmd.nasa.gov/records/GCMD_GNV00005.html). The system has been compared to more sophisticated, mechanistic simulation models, and the Holdridge implementations generally showed similar or greater climate sensitivity with respect to spatial distribution of vegetation (Yates et al., 2000).

We did some preliminary comparisons with Maxent (Phillips et al., 2004, 2006), a species habitat–modeling program, using climate as a predicting variable. We found that the program consistently predicted areas where studied species do not occur. A Holdridge vs. Maxent comparison would be interesting, but at present we believe that under our circumstances of well–sampled taxa, computation resources, and model expertise, simple correlational models, such as Holdridge, may be of greater advantage.

4. – When overlaying collection sites on the Holdridge Life Zones, we followed Morrone's suggestions (2000) regarding the formal preparation of a biogeographic atlas, the elaboration of a distribution database and detailed locality and endemism maps. The base electronic map was derived from the one presented in Atlas Costa Rica 2000 (Instituto Tecnológico de Costa Rica, 2000).

5. – To create comparable maps for the different taxonomic groups of this study, the ranking levels of species richness and endemism by life zone were calculated in accordance with the classification used for the dung beetles of Costa Rica (Coleoptera: Scarabaeinae), as defined by Kohlmann et al. (2007) in a previous study. Accordingly, 5 species richness levels were established arbitrarily: up to 7% of the maximum species richness in a single life zone (class 1), up to 20% (class 2), up to 44% (class 3), up to 70% (class 4) and more than 70% (class 5) . For the sake of this analysis and comparative purposes, only the 2 highest ranks (ranks 4 and 5) were shown and discussed, allowing us to focus the analysis on the richer and therefore more representative areas.

Concerning endemism, the limits for the 5 classes were set up arbitrarily as: up to 12% of maximum number of endemic species in a single life zone for class 1, with 24%, 46%, 72%, and > 72% for classes 2 through 5, respectively. For each taxonomic group these relative values were converted into absolute values of species richness and endemism. Again, only the 2 most numerous ranks were used, following the logic outlined in the previous section.

6. – A conservation priority map was elaborated by overlaying maps of species numbers and endemics over a protected areas map to calculate percentages of areas under protection. Each of these 2 maps (number of species and endemics derived from step 5) indicated 5 different taxa classes with values 1–5, as defined by Kohlmann et al. (2007) in a previous study, where class 5 is the class with the highest number of taxa. Subsequently, the combination of species richness and endemism ranks by life zones was used to define 6 conservation priority areas in a gap analysis map according to Table 1. This differs from our previous approach (Kohlmann et al., 2007), where only 4 levels could be generated. The highest level (Priority 1) is assigned to life zones with top ranks both in species richness and endemism. The lowest priority level (Priority 6) , results from a combination "rank 4 in species richness" and "rank<4 in endemism". Intermediate combinations define the priority levels 2 to 5 (Table 1).

This method of priority definition using complementarity (degree to which an area contributes otherwise unrepresented species to a set of areas), picturing the combination of areas of greatest species and endemism richness, was chosen following the suggestion made by Williams et al. (1996). They found that the areas chosen by using complementarity represented all the species many times over rather than by either choosing species or areas of endemism separately. They also found that it is also a well–suited method for supplementing an existing conservation network, in their case British birds. Equally, the decision to prioritize endemism over species richness in the definition process follows well–established recommendations expressed by Mittermeier et al. (2004), which are based on considering endemics as irreplaceable.

7.– Finally, a map showing the distribution of potential conflict areas was elaborated, overlaying the previous conservation priority areas map on a land use map. The land use map is derived from a 1992 map that was taken from the Terra Commission land ordination study for Costa Rica (Cotera et al., 1998).

 

Results

Distribution of collection localities: The collection localities indicate that the northern part of Costa Rica, as well as the Central Pacific, are under sampled, due mostly to the fact that these areas have been highly transformed by agricultural activities. Other areas that also require more collecting effort are the Nicoya Peninsula of northwestern Costa Rica and the higher parts of the Talamanca Cordillera to the southeast; the lack of roads in these regions is one of the main barriers to collecting in these areas.

Unfortunately, not all areas of Costa Rica have been collected with equal intensity. In order to deal with under sampled areas, as well as to identify the areas with a good collecting effort, and for comparative purposes, regions with a collecting effort of 5 or more years were arbitrarily chosen for this study. The subsequent analyses will be based on these regions. Figure 2 shows the Holdridge Life Zone polygons associated with these collection records.

Appendices 1–(2,3)–4 contain a list of all the taxa used in this study and relate them to the number of life zones used for mapping their distribution (Fig. 2). Additional information is also provided (Appendices 1–(2,3)–4) for categorizing the endemism status for each taxon, as well as giving the complete list of the different life zones where each taxon has been collected. Life zones areas depicted in grey (Figs. 3, 4), represent zones where no collecting efforts have been undertaken, thus indicating regions where collecting should be directed in the future.

Protection of life zone areas: Costa Rica has a total mainland area of 51 042.8 km². Out of these, 12 422.4 km² (24.3%), are under some sort of official governmental protection. Noteworthy is that 100% of the total area of the montane rain forest (lower montane transition) (rf–M LM) and the subalpine rain paramo (rp–SA) are protected. Other life zones with a high percentage of its area under protection include the premontane rain forest (basal transition) (rf–P Basal) (99.9%), montane rain forest (rf–M) (89.8%), and lower montane rain forest (rf–LM) (78.6%). All other life zones have less than 50% of their area under protection (Table 2).

Distribution of species richness by life zone: It should be noted that the highest species richness zones do not present spatial correspondence for the 4 taxa at the same time. Araceae and Arecaceae (Fig. 3a–b) show the same zones of highest species richness in the tropical wet forest (wf–T) along the border with Nicaragua and the Osa Peninsula. On the contrary, Bromeliaceae and Scarabaeinae (Fig. 3c–d) show highest species richness in the premontane wet forest (wf–P), along the slopes of the Guanacaste, Tilarán and Central mountain ranges.

In relation to second rank zones, all 4 taxonomic groups correspond spatially with the tropical wet forest (wf–T) (Fig. 3a–d); all 3 plant families do so in the premontane rain forest; Araceae and Arecaceae in the lower montane rain forest (rf–LM); Araceae and Bromeliaceae in the premontane wet forest (wf–P); Araceae and Scarabaeinae in the tropical moist forest (mf–T); and finally the Arecaceae also show a second rank zone in the tropical wet forest (premontane transition) (mf–T Prem). The Pacific Northwest shows the lowest species richness ranks for all 4 taxa, as expected for a drier region. Distribution of endemism by life zone: We mapped the total number of endemic species (strictly endemic plus shared with Nicaragua and/or Panama) by life zone.

As was the case with the previous analysis, no spatial correspondences of the highest endemism zones exist for all 4 taxa (Fig. 4a–d). The only common zones are the tropical wet forest (wf–T) of Osa Peninsula between the Araceae and Arecaceae, the lower montane rain forest (rf–LM) between Araceae and Bromeliaceae, and the premontane rain forest (rf–P) between the Araceae and the Arecaceae. Interestingly, no spatial correspondence exists between the insect and the plant groups.

Several spatial correspondences occur for the second rank (Fig. 4a–d). Arecaceae, Bromeliaceae and Scrabaeinae in the premontane rain forest (rf–P); Araceae, Arecaceae and Scarabaeinae in the tropical wet forest (wf–T); Arecaceae and Scarabaeinae in the tropical wet forest (premontane transition) (wf–T Prem); Araceae and Scarabaeinae in the premontane wet forest (wf–P); Bromeliaceae and Scarabaeinae in the lower montane rain forest (rf–LM) and the lower montane wet forest (wf–LM); and finally the Arecaceae shows a second rank area in the tropical moist forest (mf–T).

Representativity of the protected areas: An analysis of the totality of the species for each of the 4 studied groups (Araceae, 29; Arecaceae, 107; Bromeliaceae, 187, and Scarabaeinae, 174) indicates that 205, 95, 156, and 165 species, respectively, are present in protected areas. Likewise, an analysis for the total number of endemics for each of the 4 groups under study (Araceae, 113; Arecaceae, 50; Bromeliaceae, 80, and Scarabaeinae, 66) indicates that 97, 40, 64, and 64 species, respectively, are present in protected areas.

Distribution of priority conservation areas: Six priority conservation categories were previously defined; however, not all priority levels necessarily exist for every taxon under study (Fig. 5a–d).

Araceae (Fig. 5a) and Arecaceae (Fig. 5b) have priority conservation areas 1 and 2 under official protection in 38% and 73% and 52% and 31,4% of their total areas, respectively; Bromeliaceae (Fig. 5c) and Scarabaeinae (Fig. 5d) have only priority conservation areas 1 (no priority areas 2 are present) under official protection in 75% and 13% of their total areas, respectively.

Distribution patterns within transformed areas: Different priority conservation areas were superimposed on a land use map (1992) in order to correlate these areas with possible land use threats (Fig. 6a–d).

The Araceae analysis (Fig. 6a) shows that priority conservation area 1 has approximately 64% of its area as forest; approximately 17% is now converted to pasture, the main threat to this area. Priority conservation area 2 is approximately 93% forested and is under no apparent threat.

For the Arecaceae (Fig. 6b), approximately 77.5% of priority conservation area 1 is forested and approximately 11% is under pasture use. Priority conservation area 2 is approximately 70% forested, whereas the biggest possible threat seems to derive from pasture, 23% of this zone being under this type of use.

In the case of the Bromeliaceae (Fig. 6c), approximately 91% of the priority conservation area 1 is forested and only 6% is under pasture use. Priority conservation area 2 is not present for this taxon.

Finally, for the Scarabaeinae (Fig. 6d), only 35% of the priority conservation area 1 is forested, whereas pasture (approximately 31%) and agriculture (approximately 27.5%) have made strong inroads into this category. Priority conservation area 2 is not present for this taxon.

Zones of highest species richness per life zone: There were 4 zones with highest species richness (Fig. 7a) according to the species richness overlay (Fig. 3a–d): the first 2 are the tropical wet forests (wf–T) in the northeastern corner, bordering Nicaragua (although most probably the central and southern Caribbean coast might also have high numbers that will become evident after a more intense collection program is applied), and the Osa Peninsula region. It would appear that the high species richness of these lowland forests tends to diminish inland, as is the case for the tropical moist forest (mf–T) in the northern Caribbean plains, and the tropical wet forest (wf–T) along the piedmont of the Caribbean versant. Both versants share naturally a very high number of common elements to the south with Panama. The third area of highest species richness is the premontane wet forest (wf–P) (approximately 750–1 500 masl) along the Pacific versant of the Guanacaste, Tilarán and Central mountain ranges. This same approximate area was named the Pacific mid–elevation region by DeVries (1987, 1997) and was considered by him to be a very complex area because of its multiplicity of habitats and microhabitats. The same author considered this zone to be very species–rich and a major migrational corridor between the Atlantic and Pacific slopes, as well as a mixing zone for species of both slopes. This area has more species than the Talamanca mountain range to the South, which has a greater extension and is much older (Eocene) than the mountain ranges to the North (Eocene–Pleistocene) (Coates, 1997; Bergoeing, 1998; Valerio, 1999; Alvarado, 2000; Denyer and Kussmaul, 2000), thus contradicting all the tenets (time, species–area and modified species–area relationship) of the island biogeography theory. The last and fourth area is very small and is represented by the tropical wet forest (Premontane transition) (wf–T Prem) on the Caribbean versant of the Guanacaste mountain range.

The northwestern dry Pacific area of Costa Rica has been well sampled by many institutions throughout the years. However, it is evident that this area does not have a species richness level (rank 3) comparable with the Caribbean and South Pacific coasts or with the mid–elevation areas of the mountain ranges. Clearly, a dry climate with less precipitation can reduce the number of species (Townsend et al., 2008).

Areas ofhighest endemism per life zone: The areas of highest endemism (Fig. 7b) according to the overlay analysis (Fig. 4a–d), show great spatial correspondence with the previous analysis, containing the same aforementioned 3 areas. A similar situation had already been reported by Campbell (1999), who found that the majority of amphibians' species are endemic to Middle America and therefore there is a tendency of areas of high species diversity to overlap with areas of high endemism.

However, for this analysis there is also a fourth area, the lower montane rain forest (rf–LM) (approximately between 1 000 masl to 2 000 masl) on the Talamanca mountain range. The northwestern Pacific with a dry tropical forest, although well sampled, is not an area of high endemism at least for dung beetles, contrary to the high dung beetle endemism levels found in dry tropical forests along the Mexican Pacific coast (Kohlmann and Solís, 2006).

Obando (2002) reports in her study the existence of 5 major areas of endemism in Costa Rica. These areas are represented by Cocos Island, which was not considered in this study; the Golfo Dulce region (Fig. 1, O), the Cordillera Central (Fig. 1, C), the Talamanca mountain range (Fig. 1, T), and the Central Pacific region (Fig. 1, P), especially the coastal mountain ranges (Fig. 1, H and U, Herradura and Turrubares hills, respectively). The Central Valley and Talamanca mountain range represent the most important areas of endemism, containing around an 80% of the endemic species, mostly conformed by the herpetofauna, birds and flora, as well as the majority of mammals threatened with extinction (Obando, 2002). The Osa Peninsula had also already being identified as an important endemism area by several authors (DeVries, 1987, 1997; Elizondo et al., 1989; Fogden and Fogden, 1997; Savage 2002). This tropical wet forest was isolated from its Caribbean counterpart by the uplift of the Talamanca mountain range through the subduction of the Cocos Ridge beneath the Costa Rica – Panama Microplate, a process that seems to have started about 3 million years ago (Coates, 1997). This vicariant process has produced a great number of vertebrate and insect sister species on the Caribbean and Pacific sides (Kohlmann and Wilkinson, 2007).

This study supports previously proposed areas of endemism, with the exception of the Central Pacific region, which this study assigned a rank level of only 3 (Fig. 7b). However, 3 new important areas of endemism are proposed here: the premontane wet forests (wf–P) of the Tilarán and Guanacaste mountain ranges and the tropical wet forest (wf–T) of the northeastern Caribbean (Fig. 7b). These last results are important because they contradict a previous study by Elizondo et al. (1989), based on vertebrates and plants, in which the authors found no reasons to support the hypothesis that the Tilarán and Guanacaste mountain ranges could represent areas for the generation of endemics. DeVries (1987) had already defined the Guanacaste mountain range as a species pocket area– i.e. a place with rare or unusual species (not necessarily an area of endemism) and characterized by being small in area and having unusual climatic patterns. At the same time, the Caribbean lowlands have a relatively recent origin (Pliocene–Pleistocene; Bergoeing, 1998), yet are rich in endemics. The Tilarán and Guanacaste mountain ranges, as well as the Caribbean lowlands, were reported for the first time to be of importance in the generation of endemics by using dung beetles (Kohlmann et al., 2007), which is confirmed by this study's results.

Life zones with highest overall species richness: Table 3 indicates the overall species and endemics richness per group per life zone in Costa Rica. Only the life zones highlighted with a star in Table 3 have been well sampled (i.e. more than 5 years of collecting), therefore, they can be adequately compared. Table 3 also clearly shows those life zones where no members of the taxa under study have been found so far.

According to these results, the premontane rain forest (rf–P) life zone showing the highest total species richness for all plant taxa (second for the Scarabaeinae) and premontane wet forest (wf–P) for the Scarabaeinae. These life zones cover one of the largest geographical areas in the country, at altitudes ranging from 500 masl to 1 700 masl, and temperatures varying between 17 °C and 24 °C (Valerio, 2006). The upper limit of this category corresponds spatially with the frost line or with the so–called "coffee line" (Valerio, 2006).

The second life zone with the highest number of species is the tropical wet forest (wf–T) for the Araceae and Arecaceae and the lower montane rain forest (rf–LM) for the Bromeliaceae (Table 3). Tropical wet forest (wf–T) is present on both slopes. Its altitude ranges from 0 masl to 500 masl, and it has an average temperature above 24 °C (Valerio, 2006). The tropical wet forest (wf–T) is generally considered to be the most species rich ecosystem in Costa Rica (Fogden and Fogden, 1997; Valerio, 1999); however, this was not the case for the present study. These results also confirm that the dry Pacific Northwest is not a species–rich area for the studied groups, although some groups, such as legumes and cacti, which are more adapted to drier climates, are actually highly diversified in this environment (Valerio, 1999; Lomolino et al., 2006).

Life zones with highest overall endemics richness: Considering the overall number of endemics (Table 3), we arrived, not surprisingly, to an identical result as the previous analysis. The premontane rain forest (rf–P) is the life zone with the highest total endemics richness for all plant taxa (second for the Scarabaeinae) and premontane wet forest (wf–P) for the Scarabaeinae. The premontane rain forest (rf–P) is present on the Pacific, as well as on the Caribbean slopes, and although Valerio (2006) indicates that few endemic species are present in this forest type, the Araceae and Arecaceae on the Talamanca mountain range (Fig, 4a–b), and the Bromeliaceae on the Tilarán mountain range (Fig. 4c), show here their highest levels of endemism, thus supporting Obando's (2002) conclusion that the cloud forest is the most endemics–rich ecosystem of Costa Rica.

As before, the second life zone with the highest number of endemics is the tropical wet forest (wf–T) for the Araceae and Arecaceae and the lower montane rain forest (rf–LM) for the Bromeliaceae.

Number of local and regional endemics: Regarding the percentage of endemics (Table 4), local (Costa Rica) and regional (Nicaragua–Costa Rica–Panama) values are fairly high, as compared to the local (12%) and regional (28%) endemism that Savage (2002) reported for the herpetofauna of Costa Rica, which was considered to be the group with the highest endemism for the country (Obando, 2002). These figures also compare well with the estimates that Obando (2002) established for plant endemism (12%) in Costa Rica and plant (30%) and insect (18%) endemism on Cocos Island. Mammals and birds on the contrary present low values of endemism of 0.8% and 2.5%, respectively, according to Obando (2002), being this one reason for not developing a conservation analysis using only these groups.

The results also indicate that many endemic species are shared with Panama. These results seem to suggest that the use of insect and plants in particular, can give a much more detailed picture of areas of endemism than can be obtained by the sole use of vertebrates, as has been the case lately. These groups should be used as often as possible for conservation studies.

 

Discussion

Representativity of protected areas: The representativity analysis indicates that a high number (Araceae 89%, Arecaceae 89%, Bromeliaceae 83%, and Scarabaeinae 95%) of the total species are already included by the established protected area system. A similar analysis concerning endemic species also shows the presence of high numbers (Araceae 86%, Arecaceae 80%, Bromeliaceae 80%, and Scarabaeinae 97%) in these protected areas. It is possible that the numbers for plants may be slightly underestimated, because the dung beetles have been more thoroughly collected (Araceae, 2 108 localities; Arecaceae, 1 410 localities; Bromeliaceae, 1 571 localities; Scarabaeinae, 2 869 localities). It can be argued that the representation of both species and endemics in protected areas is already high. However, this fact does not guarantee their safeguarding or viability in the long run, because a range collapse could still occur. The endemic population or the community, to which it pertains, could still be marginal or vulnerable to natural or human induced processes. At present we do not have the necessary information in order to establish the minimum required area to ensure species protection.

Distribution of priority conservation areas: Information taken from the maps, which relate species and endemic species richness with current conservation areas (Figs. 7a and 7b) represented a basis for a gap analysis, by means of a conservation priority map (Fig. 7c). Priority area 1 indicates congruence between the highest species richness (rank 5) and the highest endemics (rank 5) numbers. Three areas are defined in this category: the tropical wet forest (wf–T) along the northeastern border with Nicaragua and in the Osa Peninsula and the premontane wet forest (wf–P) along the Guanacaste, Tilarán and Central mountain ranges. Priority area 2 indicates the areas where the highest endemism level (rank 5) corresponds spatially with areas below the highest species richness level (rank<5). One area is defined in this category: the lower montane rain forest (rf–LM) on the Talamanca mountain range.

Priority area 1, the biggest zone of all, has 8 201 km² and has 35% of its area under protection. Even though these numbers could be interpreted as a false sense of security, actually, the tropical wet forest is reasonably protected as can be observed from Fig. 7b, especially the area of the Osa Peninsula; however, the premontane wet forest (1 593 km²), represented mainly by cloud forest, along the Guanacaste, Tilarán and Central mountain ranges, is protected, because only 13% of its area is under protection (Kohlmann et al., 2007). Priority area 2 is represented by a total of 2 278 km² and has the highest percentage under protection (81%). The best–protected area in terms of surface area is represented by the Talamanca mountain range. Priority area 3 is the smallest area (259 km²) with 65% of its area under protection, while priority area 6 (4 519 km²) is the least protected category with 21%. All priority areas add up to 17 099 km², of which 40% are under some kind of protection, which overall could be considered a number to be improved upon.

Distribution of conflict areas: The map showing the distribution of potential conservation conflicts (Fig. 7d) is an overlay of Figure 7c on a land–use map.

Ideally, most conservation effort should be devoted to increase the area under protection for priority area 1, although this might prove difficult. In principle, 60% of it is still forested and could therefore allow an increase in protected areas, whereas 19% is under pasture and 9% under agricultural use. However, most of the potential increase in protected areas is associated with the tropical wet forest of the Caribbean and Osa Peninsula lowlands (Fig. 7d). Again, the area located along the Guanacaste, Tilarán and Central mountain ranges faces a very different situation (Fig. 7d). This area has only 35% of its land forested whereas 31% and 27% are under pasture and agriculture use, respectively. Therefore, the area has very limited possibilities of increasing protection areas and great probabilities of being overrun by pastoral–agricultural activities (Kohlmann et al., 2007). It should be remembered that this area showed one of the highest rankings in species richness for Bromeliaceae (Fig. 3c) and Scarabaeinae (Fig. 3d) and endemism for the Scarabaeinae (Fig. 4d). This area can be considered as a true biodiversity hotspot for Costa Rica and should be paramount for the official conservation planners.

Priority area 2 still has 96% of its area as forest, so there is a great opportunity for taking effective protective action. This is actually the protected area with the highest amount of forested area and is mainly located in almost uninhabited areas on the higher reaches of the Talamanca mountain range, where already the biggest conservation area, the international La Amistad Park, is located. This area is also of great importance because it represents one of the highest rankings in species richness for Bromeliaceae (Fig. 3c) and in endemism for Araceae (Fig. 4a) and Bromeliaceae (Fig. 4c).

Overall, of the 17 099 km² identified as priority areas, 67.5% are still forested and therefore show a promise of an increase in protection. It is also clear from the data that pastureland activities emerge as probably the main threat to biodiversity conservation, because of their extension (18.5%) and proximity to the priority areas, whereas agriculture occupies the second place (7.2%), and urban areas represent only a very small threat (0.16%).

A forest cover analysis showed that during the 2000–2005 period forest cover increased by 125 000 ha (2.4% of the national territory), especially in the Guanacaste Peninsula, while forest loss was in the order of 34 500 ha (Estado de la Nación, 2007). It is to be hoped that this trend may continue and contribute to the preservation of the Costa Rican biodiversity.

Representativity and complementarity: In the past, the majority of the species richness and endemism studies in Costa Rica have relied basically on vertebrate distribution analysis, especially birds and large vertebrates as indicators of human impacts on biodiversity, and more recently plants have also been employed for this purpose (Obando, 2002; SINAC, 2007a). Insects have not been prominent in these studies.

It is shown in this paper that a different and perhaps a much more refined picture can be gained by using 3 plant families and one dung beetle subfamily instead (Figs. 3, 4, 5, 6, 7). This analysis suggests the existence of 3 previously undetected areas of endemism (Fig. 7b) that had not been registered by the use of vertebrates. Although overlap between the different groups is nonrandom, it is not perfect, thus the need for analyzing as many taxonomic groups as possible. In this study, hotspots for species richness tended to overlap with hotspots of endemism (Fig. 7c), thus defining the different conservation priority zones generated by this study.

Costa Rica is perhaps the best–collected country in Central America, not only through the work of many foreign scientists, but lately through the important work done by the INBio (Obando, 2007). Still, some areas have been under collected, but the available information allows us to elucidate general patterns.

This analysis attempts to be a complementary representation and contribution to the excellent proposal presented by the National System of Conservation Areas of Costa Rica (Sistema Nacional de Áreas de Conservación (SINAC), 2007b). Such analysis, however, did follow a different conceptual and methodological approach by defining a conservation strategy oriented toward the necessity of representativity of selected species (plant and vertebrate species listed as endemic, red list and zero extinction), ecological systems and connectivity of core areas. The SINAC (2007b) thus proposed the undertaking of the project entitled "Propuesta de Ordenamiento Territorial para la Conservación de la Biodiversidad de Costa Rica" (Proposal of Territorial Ordination for the Conservation of Biodiversity in Costa Rica). The aim of the project is to maintain representative samples of the natural richness of the country, correlating them with productive activities of national or local importance that are conservation–compatible by supporting its conservation planning strategy mostly on a phytogeographic system that would act as a biodiversity surrogate. In the specific case of the terrestrial environment the aim was to identify vegetation types that are not adequately represented by the present net of conservation areas.

However, a recent study by Rodrigues and Brooks (2007) suggests that the use of environmental data (forest types, vegetation systems, ecoregions, floristic regions, species assemblages, abiotic data) as biodiversity surrogates are substantially less effective than cross–taxon surrogates ("extent to which conservation planning based on complementary representation of species surrogates effectively represents target species", Rodrigues and Brooks, 2007: 719), where surrogacy is defined as the "extent to which conservation planning based on a particular set of biodiversity features (surrogates) effectively represents another set (targets)" (Rodrigues and Brooks, 2007:714).

Additionally, Pawar et al. (2007) carried out a very interesting conservation biogeography hierarchical analysis of cross–taxon distributional congruence in northeast India, using amphibians, reptiles, and birds from tropical rainforest sites. They found that life–history characteristics common to certain groups contribute to observed patterns of congruence. Pawar et al. (2007) also found that the analysis of biologically different subgroups can improve the resolution of congruence analysis by unveiling fine–scale differences between otherwise concordant groups, thus providing a better resolution even with single–group data. This congruence can then be used as a surrogate simplifying the processes of area prioritization and conservation. The present paper is thus a first attempt at aiming in this direction in Costa Rica and will hopefully shed some light on the urgent and necessary need for cross–taxon analyses and the prioritization of conservation areas.

 

Acknowledgements

We would like to thank foremost the Humboldt Foundation, who graciously provided the principal author with a Georg Foster stipend, which allowed the time and conditions necessary for a sabbatical leave in Germany, where the base of this study was laid in 1999 at the University of the Saarland and allowed for the establishment of scientific contacts with the German academic world. Subsequently, the principal author enjoyed 2 more years of funding by the Research Office of EARTH University, then under the coordination of Dr. Carlos Hernández, which helped the completion of this work. The National Institute of Biodiversity has also been most forthcoming in providing through the good offices of Dr. R. García the base information for this study, to them our heartfelt thanks. Special thanks are due to Dr. N. Zamora, who revised the Araceae and Arecaceae list, and to Dr. J. F. Morales for checking the Bromeliaceae list. We would also like to thank Jane Yeomans, Ramón León, Vilma Obando, and 2 anonymous reviewers for the critical reading of this manuscript. Last but not least, we would also like to thank NASA for the synthetic aperture radar map (SAR) (Fig. 1) of Costa Rica.

 

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