Review
Biogeographical and Taxonomic Biases in Tropical Forest Fragmentation Research JUSTUS P. DEIKUMAH,∗ CLIVE A. MCALPINE, AND MARTINE MARON Landscape Ecology and Conservation Group, School of Geography, Planning and Environmental Management, The University of Queensland, Brisbane, Qld 4072, Australia
Abstract: Despite several decades of research on the effects of fragmentation and habitat change on biodiversity, there remain strong biases in the geographical regions and taxonomic species studied. The knowledge gaps resulting from these biases are of particular concern if the forests most threatened with modification are also those for which the effects of such change are most poorly understood. To quantify the nature and magnitude of such biases, we conducted a systematic review of the published literature on forest fragmentation in the tropics for the period 1980–2012. Studies included focused on any type of response of single species, communities, or assemblages of any taxonomic group to tropical forest fragmentation and on fragmentationrelated changes to forests. Of the 853 studies we found in the SCOPUS database, 64% were conducted in the Neotropics, 13% in Asia, 10% in the Afrotropics, and 5% in Australasia. Thus, although the Afrotropics is subject to the highest rates of deforestation globally, it was the most disproportionately poorly studied biome. Significant taxonomic biases were identified. Of the taxonomic groups considered, herpetofauna was the least studied in the tropics, particularly in Africa. Research examining patterns of species distribution was by far the most common type (72%), and work focused on ecological processes (28%) was rare in all biomes, but particularly in the Afrotropics and for fauna. We suggest research efforts be directed toward less-studied biogeographic regions, particularly where the threat of forest fragmentation continues to be high. Increased research investment in the Afrotropics will be important to build knowledge of threats and inform responses in a region where almost no efforts to restore its fragmented landscapes have yet begun and forest protection is arguably most tenuous. Keywords: Afrotropics, biogeographic bias, deforestation, fauna population decline, taxonomic bias, tropical forest biomes Sesgos Biogeogr´aficos y Taxon´ omicos en la Investigaci´ on de la Fragmentaci´ on de Bosques Tropicales
Resumen: A pesar de varias d´ecadas de investigaci´on sobre los efectos de la fragmentaci´on y el cambio de h´ abitat sobre la biodiversidad, aun persisten sesgos fuertes en las regiones geogr´ aficas y especies taxon´ omicas estudiadas. Los vac´ıos en el conocimiento que resultan de estos sesgos son de importancia particular si los bosques con mayor amenaza de modificaci´ on tambi´en son aquellos para los cuales los efectos de dicho cambio est´ an entendidos pobremente. Para cuantificar la naturaleza y la magnitud de dichos sesgos llevamos a cabo una revisi´ on sistem´ atica de la literatura publicada sobre la fragmentaci´ on de bosques tropicales en el periodo de 1980 a 2012. Los estudios incluyeron aquellos enfocados en cualquier tipo de respuesta de una sola especie, comunidad o conjunto de cualquier grupo taxon´ omico a la fragmentaci´ on del bosque; y aquellos enfocados en los cambios en los bosques relacionados con la fragmentaci´ on. Los campos biogeogr´ aficos tropicales estuvieron sujetos a las tasas m´ as grandes de p´erdida de bosque, y el menor n´ umero de estudios publicados fue sobre ellos. De los 853 estudios que encontramos en la base de datos SCOPUS, 64% se llevaron a cabo en la zona neotropical, 13% en Asia, 10% en la zona afrotropical, y 5% en Australasia. As´ı, aunque la zona afrotropical est´ a sujeta a la tasa m´ as alta de deforestaci´ on a nivel global, fue el bioma con menor estudio. Se identificaron sesgos taxon´ omicos significativos. De los grupos taxon´ omicos considerados, la herpetofauna fue la menos ´ estudiada, particularmente en Africa. La investigaci´ on encargada de examinar los patrones de distribuci´ on fue por mucho el tipo m´ as com´ un (72%) y el trabajo enfocado en los procesos ecol´ ogicos (28%) fue raro para
∗ Address
correspondence to J. P. Deikumah, email [email protected] Paper submitted August 30, 2012; revised manuscript accepted March 28, 2014.
1 Conservation Biology, Volume 00, No. 0, 1–10 C 2014 Society for Conservation Biology DOI: 10.1111/cobi.12348
Biases in Forest Fragmentation Research
2
todos los biomas, pero particularmente en la zona afrotropical y para la fauna. Sugerimos que los esfuerzos de investigaci´ on sean dirigidos hacia las regiones biogeogr´ aficas menos estudiadas, particularmente donde la amenaza de la fragmentaci´ on de bosques sigue siendo alta. La inversi´ on incrementada para la investigaci´ on en los Afrotr´ opicos ser´ a importante para obtener conocimiento de amenazas e informar respuestas en una regi´ on donde casi no se han iniciado esfuerzos para restaurar sus terrenos fragmentados y la protecci´ on de los bosques a lo mucho es poco convincente.
Palabras Clave: Afrotr´opicos, biomas de bosque tropical, deforestaci´on, declinaci´on poblacional de fauna, sesgo biogeogr´afico, sesgo taxon´ omico
Introduction Although tropical forest biomes cover 50%) within the tropics in each of the 4 forest biogeographic realms. The forest resources assessment (FRA) data by the FAO are the primary source of information on changes in global forest cover (FAO 2010). Nevertheless, these data have limitations, including differences in methods used by different countries to define and quantify forest change and reporting net values of forest cover change rather than deforestation and afforestation rates (Grainger 2008, 2010; Hansen et al. 2010). Although several Earth observation data sets can be used to mitigate these limitations (Hansen et al. 2010), we used the FRA data because we needed comparable information on net deforestation over a longer period than was available from such data sets. Therefore, although the figures are unlikely to be perfect reflections of all forest cover change within the tropics, they provide a useful index of large-scale forest cover trends among regions. The figures for annual forest cover change in these regions from 1990 to 2000 were compiled and compared with those for 2000–2010 (Fig. 1). Literature Search We used the SCOPUS database for 1980–2012 to conduct a systematic literature search of the ecological peer
Deikumah et al.
3
2000-2010
Afrotropics
Asia
Tropical biogeographic realm
Global
1990-2000
Australasia
Neotropics
-1
-0.8
-0.6
-0.4
-0.2
0
Annual change in forest cover (%)
reviewed literature. We used the following key search items forest AND fragment∗ AND tropic∗ . We screened all articles from the title through the abstract and full text to determine whether they met our criteria for inclusion. Studies included focused on any type of response of single species, communities, or assemblages of any taxonomic group to tropical forest fragmentation and on fragmentation-related changes to forests (structure of forest, edge effects, and anthropological effects). We also included studies on habitat loss because of the close relationship between habitat loss and fragmentation, but we excluded those conducted in naturally fragmented landscapes. Because we were primarily interested in studies of forest fragmentation effects on terrestrial biodiversity, we excluded studies concerned with paleoecology and speciation, climatology, aquatic and marine ecology, hydrology, and weather patterns (Supporting Information). Articles were collected from all English-language journals in the SCOPUS database (Supporting Information). Although the official language of most tropical forested countries is not English, most ecological research papers are published in English-language journals, and we do not anticipate that our focus on such journals biased the results, although some relevant articles may have been overlooked. Biogeographical and Taxonomic Biases We used the selected papers to create a database with the following details: specific geographic location of the
0.2
Figure 1. Changes in tropical forest cover in biogeographic realms from 1990 to 2000 (black bars) and from 2000 to 2010 (white bars). Compiled from the State of the World’s Forest Report (FAO 2009, 2010).
study; biogeographic realm (Afrotropical, Neotropical, Australasian, Asian [Indo-Malay], global) studied; taxonomic group investigated (plants, mammals, birds, herpetofauna, invertebrates, and ecosystems); focus of research (distribution, interaction, condition, genetics, and behavior [defined below]); and type of research conducted (empirical, review, and modeling). We categorized studies into 5 broad types that reflected the focus of the study. Studies that examined species- or assemblage-level responses with presence or absence or abundance data were categorized as distribution studies. We considered the remaining categories of study focus more process oriented. Studies related to interactions including plant–animal (e.g., pollination and seed dispersal) and interspecific interactions (e.g., predator-prey interactions, nest predation) were grouped as interaction studies. Our condition category included all studies that compared physiological and physical condition responses with fragmentation and habitat loss (e.g., reproductive physiology, body, or physiological condition), whereas the genetics category included studies involving population and molecular genetics. The behavior category included all studies relating to movement and other behaviors such as foraging and breeding. Our categorization of tropical biogeographic realms into 4 realms followed the broad categorization of Olson et al. (2001) and the United Nations GeoScheme for classification of subregions (UNSD 2011). This classification system divides the world into 8 biogeographical realms based on ecoregion delineations from numerous previous
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biogeographical studies (Udvardy 1975) and provides a useful framework for conducting biogeographical or macroecological research (UNEP-WCWC 2011). Comparisons among categories based on further subdivision into multiple smaller ecoregions were not explored to ensure that adequate numbers of publications would be available per region. We summarized the proportions of different types of studies by region and focal taxa. This allowed us to examine the magnitude of the biases in the number of published papers on tropical forest fragmentation regarding biogeographic location and taxonomic groups. We included only papers originating from the tropics and analyzed only forest loss figures for tropical regions.
graphic realms and both their respective proportions of forest cover retained and their rates of forest cover loss (Fig. 3). Of the 853 studies, 64%, 13%, and 10% were conducted in the Neotropics, Asia, and the Afrotropics, respectively, and 8% focused on global forest fragmentation issues (Fig. 3). The fewest studies (5%) were recorded from the Australasian realm (Fig. 3), which has the least tropical forest cover. Of the 853 studies, almost 72% used empirical data; the remainder focused on theory or modeling (15%), review (12%), or a combination of these approaches (1%). From 2005 to 2012, 68% of studies were conducted in the Neotropics, and 12% and 18%, respectively, were from the Afrotropics and Asia. Taxonomic Biases
Results Extent and Global Loss of Tropical Forest Net global tropical deforestation rates decreased from 0.43% (1,053,700 km2 ) per annum from 1990 to 2000 to 0.29% (711,247 km2 ) per annum from 2000 to 2010 (Fig. 1). However, this pattern varied among the 4 biogeographic regions (Fig. 1). The Asian tropical biogeographic realm had the highest annual forest loss rate of 0.77% from 1990 to 2000, but this decreased from 2000 to 2010 by approximately 50% (to 0.39%). The net deforestation rate from 1990 to 2000 in the Afrotropics was 0.56%, and it remained similar (0.52%) from 2000 to 2010 (Fig. 1). The rate of deforestation in the Neotropics was 0.40% from 1990 to 2000, and it decreased by 18% (to 0.33%) from 2000 to 2010. There was a shift in tropical forest cover change from a gain of 0.09% per annum (1990–2000) to a loss of 0.13% (2000–2010) in the Australasian region (Fig. 1). More recently (2000–2010), net deforestation rates as a percentage of forest remaining were highest in tropical Africa and showed less deceleration from the previous period relative to the other major tropical forest biomes. Biogeographical Biases Of 1092 studies, we examined in our literature search, 853 from 160 ecological journals were focused on tropical forest fragmentation and its effects on biodiversity and met our inclusion criteria (full details in Supporting Information). The amount of published tropical forest fragmentation research increased rapidly over the period we considered (Fig. 2). About 90% of all studies were conducted after 1995. This increase was driven primarily by research in the Neotropics 5 (Fig. 2). Only since 2005 was an increase in the number of studies from the Afrotropical and Asian regions noticeable (Fig. 2). There were significant mismatches between the proportion of studies conducted in the different biogeo-
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The most commonly examined taxonomic group was plants (45% of studies), whereas mammals were the most studied faunal group (20% of studies) and herpetofauna the least studied (3% of studies) (Fig. 4). The proportion of studies on different taxa varied among regions. Of the studies done in Australasia, 29% were on plants, whereas in the Neotropics, 52% were on plants. Thirty-six percent of the studies conducted in the Afrotropics focused on birds, whereas 16% focused on birds across all regions. Research in the Australasian region disproportionately focused on mammals (45%). In the other tropical regions, 12% of studies were on mammals. Studies on herpetofauna were rare in all 4 biogeographic regions (Fig. 4). Research Focus Research based on distributional data (e.g., presence or absence or abundance) was most common, and there was little process-focused work, particularly for fauna. Overall, research into patterns of distribution dominated 597 studies (70%), but this varied among taxonomic groups, ranging from 80% of studies on invertebrates to 58% of studies on plants (Fig. 5). Relatively, few studies (10 studies found in the SCOPUS database (Appendix S2) are available online. The authors are solely responsible for the content and functionality of these materials. Queries (other than absence of the material) should be directed to the corresponding author. Literature Cited Achard, F., Hugh, D. Eva, H.-J. Stibig, P. Mayaux, J. Gallego, T. Richards, and J.-P. Malingreau. 2002. Determination of deforestation rates of the world’s humid tropical forests. Science 297:999–1002. Ahrends, A., et al. 2011. Funding begets biodiversity. Diversity and Distributions 17:191–200. Annan, K. 2003. A challenge to the world’s scientists (www. sciencemag.org). Science 299:1485. Balmford, A., and W. Bond. 2005. Trends in the state of nature and their implications for human well-being. Ecology Letters 8:1218–1234. Balmford, A., J. L. Moore, T. Brooks, N. Burgess, L. A. Hansen, P. Williams, and C. Rahbek. 2001. Conservation conflicts across Africa. Science 291:2616–2619. Beier, P., M. Van Drielen, and B. O. Kankam. 2002. Avifaunal collapse in West African forest fragments. Conservation Biology 16:1097–1111. Bowen, M. E., C. A. McAlpine, L. M. Seabrook, A. P. N. House, and G. C. Smith. 2009. The age and amount of regrowth forest in fragmented brigalow landscapes are both important for woodland dependent birds. Biological Conservation 142:3051–3059. Clark, D. B. 1985. Ecological field studies in the tropics: geographical origin of reports. Bulletin of the Ecological Society of America 66:6– 9. Clark, J. A., and M. R. May. 2002. Taxonomic bias in conservation research. Science, New Series 297:191–192. Cooke, S. J., and C. M. O’Connor. 2010. Making conservation physiology relevant to policy makers and conservation practitioners. Conservation Letters 3:159–166.
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drivers. Annual Review of Ecology, Evolution, and Systematics 40: 529–549. Lindsell, J. A., K. Erik, and A. M. Siaka. 2011. The impact of civil war on forest wildlife in West Africa: mammals in Gola Forest, Sierra Leone. Oryx 45:69–77. Malhi, Y., S. Adu-Bredu, R. A. Asare, S. L. Lewis, and P. Mayaux. 2013. African rainforests: past, present and future. Philosophical Transactions of the Royal Society B: Biological Sciences 368(1625) 20120312. Manu, S., W. Peach, and W. Cresswell. 2007. The effects of edge, fragment size and degree of isolation on avian species richness in highly fragmented forest in West Africa. Ibis 149: 287–297. Mayaux, P., P. Holmgren, F. Achard, H. Eva, H.-J. Stibig, and A. Branthomme. 2005. Tropical forest cover change in the 1990s and options for future monitoring. Philosophical Transactions of the Royal Society B: Biological Sciences 360:373–384. Mayaux, P., et al. 2013. State and evolution of the African rainforests between 1990 and 2010. Philosophical Transactions of the Royal Society B: Biological Sciences 368(1625) 20120300. Mittermeier, R. A., N. Myers, J. B. Thomsen, G. A. B. D. Fonseca, and S. Olivieri. 1998. Biodiversity hotspots and major tropical wilderness areas: approaches to setting conservation priorities. Conservation Biology 12:516–520. Myers, N. 1988. Threatened biotas: “hot spots” in tropical forests. The Environmentalist 8:187–208. Myers, N. 1990. The biodiversity challenge: expanded hot-spots analysis. The Environmentalist 10:244–256. Myers, N. 2003. Conservation of biodiversity: How are we doing? The Environmentalist 23:9–15. Olson, D. M., et al. 2001. Terrestrial scoregions of the world: a new map of life on earth. BioScience 51:933–938. Pfeifer, M., N. D. Burgess, R. D. Swetnam, P. J. Platts, S. Willcock, and R. Marchant. 2012. Protected areas: mixed success in conserving East Africa’s evergreen forests. PLoS ONE 7 DOI: 10.1371/journal.pone.0039337. Platts P. J., R. E., Gereau, N. D., Burgess, and R. Marchant. 2013. Spatial heterogeneity of climate change in an Afromontane centre of endemism. Ecography 36:518–530. Pyˇsek, P., D. M. Richardson, J. Pergl, V. Jaroˇs´ık, Z. Sixtov´a, and E. Weber. 2008. Geographical and taxonomic biases in invasion ecology. Trends in Ecology & Evolution 23:237–244. Ros-Tonen, M. A. F., and T. Dietz. 2005. African frorests between nature and livelihood resources: interdisciplinary studies in conservation and forest management. The Edwin Mellen Press, Lewiston, USA. Rudel, T. K., R. Defries, G. P. Asner, and W. F. Laurance. 2009. Changing drivers of deforestation and new opportunities for conservation. Conservation Biology 23:1396–1405. Schiesari, L., B. Grillitsch, and H. Grillitsch. 2007. Biogeographic biases in research and their consequences for linking amphibian declines to pollution. Conservation Biology 21:465–471. Schmitt, C. B., et al. 2009. Global analysis of the protection status of the world’s forests. Biological Conservation 142:2122–2130. Sitas, N., J. E. M. Baillie, and N. J. B. Isaac. 2009. What are we saving? Developing a standardized approach for conservation action. Animal Conservation 12:231–237. Sodhi, N. S., and L. H. Liow. 2000. Improving conservation biology research in Southeast Asia. Conservation Biology 14: 1211–1212. Stocks, G., L. Seales, F. Paniagua, E. Maehr, and M. E. Bruna. 2008. The geographical and institutional distribution of ecological research in the tropics. Biotropica 40:397–404. Strassburg, B., A. Creed, and R. Ashton. 2009. Policy briefs 1: Distribution of terrestrial carbon across developing countries, Terrestrial Carbon Group (TCG). H. John Heinz III Center for Science.
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Biogeographical and Taxonomic Biases in Tropical Forest Fragmentation Research JUSTUS P. DEIKUMAH,∗ CLIVE A. MCALPINE, AND MARTINE MARON Landscape Ecology and Conservation Group, School of Geography, Planning and Environmental Management, The University of Queensland, Brisbane, Qld 4072, Australia
Abstract: Despite several decades of research on the effects of fragmentation and habitat change on biodiversity, there remain strong biases in the geographical regions and taxonomic species studied. The knowledge gaps resulting from these biases are of particular concern if the forests most threatened with modification are also those for which the effects of such change are most poorly understood. To quantify the nature and magnitude of such biases, we conducted a systematic review of the published literature on forest fragmentation in the tropics for the period 1980–2012. Studies included focused on any type of response of single species, communities, or assemblages of any taxonomic group to tropical forest fragmentation and on fragmentationrelated changes to forests. Of the 853 studies we found in the SCOPUS database, 64% were conducted in the Neotropics, 13% in Asia, 10% in the Afrotropics, and 5% in Australasia. Thus, although the Afrotropics is subject to the highest rates of deforestation globally, it was the most disproportionately poorly studied biome. Significant taxonomic biases were identified. Of the taxonomic groups considered, herpetofauna was the least studied in the tropics, particularly in Africa. Research examining patterns of species distribution was by far the most common type (72%), and work focused on ecological processes (28%) was rare in all biomes, but particularly in the Afrotropics and for fauna. We suggest research efforts be directed toward less-studied biogeographic regions, particularly where the threat of forest fragmentation continues to be high. Increased research investment in the Afrotropics will be important to build knowledge of threats and inform responses in a region where almost no efforts to restore its fragmented landscapes have yet begun and forest protection is arguably most tenuous. Keywords: Afrotropics, biogeographic bias, deforestation, fauna population decline, taxonomic bias, tropical forest biomes Sesgos Biogeogr´aficos y Taxon´ omicos en la Investigaci´ on de la Fragmentaci´ on de Bosques Tropicales
Resumen: A pesar de varias d´ecadas de investigaci´on sobre los efectos de la fragmentaci´on y el cambio de h´ abitat sobre la biodiversidad, aun persisten sesgos fuertes en las regiones geogr´ aficas y especies taxon´ omicas estudiadas. Los vac´ıos en el conocimiento que resultan de estos sesgos son de importancia particular si los bosques con mayor amenaza de modificaci´ on tambi´en son aquellos para los cuales los efectos de dicho cambio est´ an entendidos pobremente. Para cuantificar la naturaleza y la magnitud de dichos sesgos llevamos a cabo una revisi´ on sistem´ atica de la literatura publicada sobre la fragmentaci´ on de bosques tropicales en el periodo de 1980 a 2012. Los estudios incluyeron aquellos enfocados en cualquier tipo de respuesta de una sola especie, comunidad o conjunto de cualquier grupo taxon´ omico a la fragmentaci´ on del bosque; y aquellos enfocados en los cambios en los bosques relacionados con la fragmentaci´ on. Los campos biogeogr´ aficos tropicales estuvieron sujetos a las tasas m´ as grandes de p´erdida de bosque, y el menor n´ umero de estudios publicados fue sobre ellos. De los 853 estudios que encontramos en la base de datos SCOPUS, 64% se llevaron a cabo en la zona neotropical, 13% en Asia, 10% en la zona afrotropical, y 5% en Australasia. As´ı, aunque la zona afrotropical est´ a sujeta a la tasa m´ as alta de deforestaci´ on a nivel global, fue el bioma con menor estudio. Se identificaron sesgos taxon´ omicos significativos. De los grupos taxon´ omicos considerados, la herpetofauna fue la menos ´ estudiada, particularmente en Africa. La investigaci´ on encargada de examinar los patrones de distribuci´ on fue por mucho el tipo m´ as com´ un (72%) y el trabajo enfocado en los procesos ecol´ ogicos (28%) fue raro para
∗ Address
correspondence to J. P. Deikumah, email [email protected] Paper submitted August 30, 2012; revised manuscript accepted March 28, 2014.
1 Conservation Biology, Volume 00, No. 0, 1–10 C 2014 Society for Conservation Biology DOI: 10.1111/cobi.12348
Biases in Forest Fragmentation Research
2
todos los biomas, pero particularmente en la zona afrotropical y para la fauna. Sugerimos que los esfuerzos de investigaci´ on sean dirigidos hacia las regiones biogeogr´ aficas menos estudiadas, particularmente donde la amenaza de la fragmentaci´ on de bosques sigue siendo alta. La inversi´ on incrementada para la investigaci´ on en los Afrotr´ opicos ser´ a importante para obtener conocimiento de amenazas e informar respuestas en una regi´ on donde casi no se han iniciado esfuerzos para restaurar sus terrenos fragmentados y la protecci´ on de los bosques a lo mucho es poco convincente.
Palabras Clave: Afrotr´opicos, biomas de bosque tropical, deforestaci´on, declinaci´on poblacional de fauna, sesgo biogeogr´afico, sesgo taxon´ omico
Introduction Although tropical forest biomes cover 50%) within the tropics in each of the 4 forest biogeographic realms. The forest resources assessment (FRA) data by the FAO are the primary source of information on changes in global forest cover (FAO 2010). Nevertheless, these data have limitations, including differences in methods used by different countries to define and quantify forest change and reporting net values of forest cover change rather than deforestation and afforestation rates (Grainger 2008, 2010; Hansen et al. 2010). Although several Earth observation data sets can be used to mitigate these limitations (Hansen et al. 2010), we used the FRA data because we needed comparable information on net deforestation over a longer period than was available from such data sets. Therefore, although the figures are unlikely to be perfect reflections of all forest cover change within the tropics, they provide a useful index of large-scale forest cover trends among regions. The figures for annual forest cover change in these regions from 1990 to 2000 were compiled and compared with those for 2000–2010 (Fig. 1). Literature Search We used the SCOPUS database for 1980–2012 to conduct a systematic literature search of the ecological peer
Deikumah et al.
3
2000-2010
Afrotropics
Asia
Tropical biogeographic realm
Global
1990-2000
Australasia
Neotropics
-1
-0.8
-0.6
-0.4
-0.2
0
Annual change in forest cover (%)
reviewed literature. We used the following key search items forest AND fragment∗ AND tropic∗ . We screened all articles from the title through the abstract and full text to determine whether they met our criteria for inclusion. Studies included focused on any type of response of single species, communities, or assemblages of any taxonomic group to tropical forest fragmentation and on fragmentation-related changes to forests (structure of forest, edge effects, and anthropological effects). We also included studies on habitat loss because of the close relationship between habitat loss and fragmentation, but we excluded those conducted in naturally fragmented landscapes. Because we were primarily interested in studies of forest fragmentation effects on terrestrial biodiversity, we excluded studies concerned with paleoecology and speciation, climatology, aquatic and marine ecology, hydrology, and weather patterns (Supporting Information). Articles were collected from all English-language journals in the SCOPUS database (Supporting Information). Although the official language of most tropical forested countries is not English, most ecological research papers are published in English-language journals, and we do not anticipate that our focus on such journals biased the results, although some relevant articles may have been overlooked. Biogeographical and Taxonomic Biases We used the selected papers to create a database with the following details: specific geographic location of the
0.2
Figure 1. Changes in tropical forest cover in biogeographic realms from 1990 to 2000 (black bars) and from 2000 to 2010 (white bars). Compiled from the State of the World’s Forest Report (FAO 2009, 2010).
study; biogeographic realm (Afrotropical, Neotropical, Australasian, Asian [Indo-Malay], global) studied; taxonomic group investigated (plants, mammals, birds, herpetofauna, invertebrates, and ecosystems); focus of research (distribution, interaction, condition, genetics, and behavior [defined below]); and type of research conducted (empirical, review, and modeling). We categorized studies into 5 broad types that reflected the focus of the study. Studies that examined species- or assemblage-level responses with presence or absence or abundance data were categorized as distribution studies. We considered the remaining categories of study focus more process oriented. Studies related to interactions including plant–animal (e.g., pollination and seed dispersal) and interspecific interactions (e.g., predator-prey interactions, nest predation) were grouped as interaction studies. Our condition category included all studies that compared physiological and physical condition responses with fragmentation and habitat loss (e.g., reproductive physiology, body, or physiological condition), whereas the genetics category included studies involving population and molecular genetics. The behavior category included all studies relating to movement and other behaviors such as foraging and breeding. Our categorization of tropical biogeographic realms into 4 realms followed the broad categorization of Olson et al. (2001) and the United Nations GeoScheme for classification of subregions (UNSD 2011). This classification system divides the world into 8 biogeographical realms based on ecoregion delineations from numerous previous
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biogeographical studies (Udvardy 1975) and provides a useful framework for conducting biogeographical or macroecological research (UNEP-WCWC 2011). Comparisons among categories based on further subdivision into multiple smaller ecoregions were not explored to ensure that adequate numbers of publications would be available per region. We summarized the proportions of different types of studies by region and focal taxa. This allowed us to examine the magnitude of the biases in the number of published papers on tropical forest fragmentation regarding biogeographic location and taxonomic groups. We included only papers originating from the tropics and analyzed only forest loss figures for tropical regions.
graphic realms and both their respective proportions of forest cover retained and their rates of forest cover loss (Fig. 3). Of the 853 studies, 64%, 13%, and 10% were conducted in the Neotropics, Asia, and the Afrotropics, respectively, and 8% focused on global forest fragmentation issues (Fig. 3). The fewest studies (5%) were recorded from the Australasian realm (Fig. 3), which has the least tropical forest cover. Of the 853 studies, almost 72% used empirical data; the remainder focused on theory or modeling (15%), review (12%), or a combination of these approaches (1%). From 2005 to 2012, 68% of studies were conducted in the Neotropics, and 12% and 18%, respectively, were from the Afrotropics and Asia. Taxonomic Biases
Results Extent and Global Loss of Tropical Forest Net global tropical deforestation rates decreased from 0.43% (1,053,700 km2 ) per annum from 1990 to 2000 to 0.29% (711,247 km2 ) per annum from 2000 to 2010 (Fig. 1). However, this pattern varied among the 4 biogeographic regions (Fig. 1). The Asian tropical biogeographic realm had the highest annual forest loss rate of 0.77% from 1990 to 2000, but this decreased from 2000 to 2010 by approximately 50% (to 0.39%). The net deforestation rate from 1990 to 2000 in the Afrotropics was 0.56%, and it remained similar (0.52%) from 2000 to 2010 (Fig. 1). The rate of deforestation in the Neotropics was 0.40% from 1990 to 2000, and it decreased by 18% (to 0.33%) from 2000 to 2010. There was a shift in tropical forest cover change from a gain of 0.09% per annum (1990–2000) to a loss of 0.13% (2000–2010) in the Australasian region (Fig. 1). More recently (2000–2010), net deforestation rates as a percentage of forest remaining were highest in tropical Africa and showed less deceleration from the previous period relative to the other major tropical forest biomes. Biogeographical Biases Of 1092 studies, we examined in our literature search, 853 from 160 ecological journals were focused on tropical forest fragmentation and its effects on biodiversity and met our inclusion criteria (full details in Supporting Information). The amount of published tropical forest fragmentation research increased rapidly over the period we considered (Fig. 2). About 90% of all studies were conducted after 1995. This increase was driven primarily by research in the Neotropics 5 (Fig. 2). Only since 2005 was an increase in the number of studies from the Afrotropical and Asian regions noticeable (Fig. 2). There were significant mismatches between the proportion of studies conducted in the different biogeo-
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The most commonly examined taxonomic group was plants (45% of studies), whereas mammals were the most studied faunal group (20% of studies) and herpetofauna the least studied (3% of studies) (Fig. 4). The proportion of studies on different taxa varied among regions. Of the studies done in Australasia, 29% were on plants, whereas in the Neotropics, 52% were on plants. Thirty-six percent of the studies conducted in the Afrotropics focused on birds, whereas 16% focused on birds across all regions. Research in the Australasian region disproportionately focused on mammals (45%). In the other tropical regions, 12% of studies were on mammals. Studies on herpetofauna were rare in all 4 biogeographic regions (Fig. 4). Research Focus Research based on distributional data (e.g., presence or absence or abundance) was most common, and there was little process-focused work, particularly for fauna. Overall, research into patterns of distribution dominated 597 studies (70%), but this varied among taxonomic groups, ranging from 80% of studies on invertebrates to 58% of studies on plants (Fig. 5). Relatively, few studies (10 studies found in the SCOPUS database (Appendix S2) are available online. The authors are solely responsible for the content and functionality of these materials. Queries (other than absence of the material) should be directed to the corresponding author. Literature Cited Achard, F., Hugh, D. Eva, H.-J. Stibig, P. Mayaux, J. Gallego, T. Richards, and J.-P. Malingreau. 2002. Determination of deforestation rates of the world’s humid tropical forests. Science 297:999–1002. Ahrends, A., et al. 2011. Funding begets biodiversity. Diversity and Distributions 17:191–200. Annan, K. 2003. A challenge to the world’s scientists (www. sciencemag.org). Science 299:1485. Balmford, A., and W. Bond. 2005. Trends in the state of nature and their implications for human well-being. Ecology Letters 8:1218–1234. Balmford, A., J. L. Moore, T. Brooks, N. Burgess, L. A. Hansen, P. Williams, and C. Rahbek. 2001. Conservation conflicts across Africa. Science 291:2616–2619. Beier, P., M. Van Drielen, and B. O. Kankam. 2002. Avifaunal collapse in West African forest fragments. Conservation Biology 16:1097–1111. Bowen, M. E., C. A. McAlpine, L. M. Seabrook, A. P. N. House, and G. C. Smith. 2009. The age and amount of regrowth forest in fragmented brigalow landscapes are both important for woodland dependent birds. Biological Conservation 142:3051–3059. Clark, D. B. 1985. Ecological field studies in the tropics: geographical origin of reports. Bulletin of the Ecological Society of America 66:6– 9. Clark, J. A., and M. R. May. 2002. Taxonomic bias in conservation research. Science, New Series 297:191–192. Cooke, S. J., and C. M. O’Connor. 2010. Making conservation physiology relevant to policy makers and conservation practitioners. Conservation Letters 3:159–166.
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