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Stockwell, Logan W.
Una encuesta de las riquezas de especies de colepteros, diversidad y abundancia en los hbitats a lo largo de un gradiente de perturbacin
A survey of Coleopteran species richness, diversity and abundance in habitats along a disturbance gradient
Three microhabitats in La Cruz, Costa Rica were surveyed for Coleopteran species richness, diversity and abundance in primary forest, secondary forest and active pasture. Survey sites correlated with levels of disturbance, which were hypothesized to reflect the availability and diversity of natural resources. A total of 865 Coleopterans were collected. Of the collected samples, 125 morpho-species and 22 families were identified. Species richness, diversity and abundance were calculated to see if they correlated with levels of habitat disturbance. It was hypothesized that natural resource abundance and diversity would be associated with levels of habitat disturbance. Forested areas with less habitat disturbance ought to have a greater variety of available resources on account of microclimate diversity and would therefore be able to sustain a greater diversity of Coleopterans. Results indicated that morpho-species richness was highest in primary forest whereas Coleopteran family analysis showed that family richness was highest in secondary forest. Results validate a correlation between habitat disturbance and Coleopteran diversity.
Tres microhabitats en la Cruz, Costa Rica fueron encuestados para conocer la riqueza de especies, la diversidad y la abundancia de colepteros en un bosque primario, en un bosque secundario y en un pastizal activo.
Text in English.
Beetles--Costa Rica--Guanacaste--La Cruz
Species diversity--Costa Rica
Escarabajos--Costa Rica--Guanacaste--La Cruz
Diversidad de especies--Costa Rica
Tropical Ecology 2008
Ecologia Tropical 2008
t Monteverde Institute : Tropical Ecology
A Survey of Coleopteran Species Richness, Diversity and Abundance in Habitats Along a Disturbance Gradient Logan W. Stockwell Department of Biology, Occidental College ABSTRACT Three microhabitats in La Cruz, Costa Rica were sur veyed for Coleopteran species richness, diversity a nd abundance in primary forest, secondary forest and a ctive pasture. Survey sites correlated with levels of disturbance, which were hypothesized to reflect the availability and diversity of natural resources. A total of 865 Coleopterans were collected. Of the collected s amples, 125 morpho-species and 22 families were identified. Species richness, diversity and abundan ce were calculated to see if they correlated with l evels of habitat disturbance. It was hypothesized that natur al resource abundance and diversity would be associ ated with levels of habitat disturbance. Forested areas with less habitat disturbance ought to have a great er variety of available resources on account of microc limate diversity and would therefore be able to sus tain a greater diversity of Coleopterans. Results indicate d that morpho-species richness was highest in prima ry forest whereas Coleopteran family analysis showed t hat family richness was highest in secondary forest Results validate a correlation between habitat dist urbance and Coleopteran diversity. Resumen Tres microhabitats en La Cruz, Costa Rica muestread os para conocer la riqueza de especies, diversidad y abundancia de coleopteros en un bosque primario, un bosque secundarios y un pastizal activo. Los siti os muestreados estan correlacionados con niveles de al teracion, los cuales son hipoteticamente los que re flejan las disponibilidad y diversidad de los recursos. U n total de 865 especies de escarabajos fueron colec tados. En las muestras colectadas, 125 morfo especies y 22 familias fueron identificadas. La riqueza de espe cies, diversidad y abundancia fue calculada para observar si la diversidad esta asociada con niveles de alte racion en el habitat. Las areas boscosas con menor altera cion en el habitat son las que presentan una mayor variedad de recursos disponibles en relacion con un a diversidad microclimatica y por lo tanto son capa ces de mantener una mayor diversidad de coleopteros. L os resultados indican que la riqueza de morfo-espec ies es mas alta en el bosque primario, mientras que la riqueza de familias es mayor en el bosque secundari o. Los resulados una correlacion entre la alteracion d el habitat y la riqueza de coleopteros. INTROUCTION Land transformation from forested habitat to agricu lture, recreation and human settlement all have distinct effects on the environment. These disturbances often result in forest fragmentation, habitat shredding and edge effects, which disrupt the ecological conditions for organisms harbored there. Forest conversion to agriculture produces hotter, drier, windier, and brighter conditions than would, in sec ondary and primary forests. It has been proven that habitat disturbances caused by human ac tivity have drastic effects on organism diversity (McNeely et al. 1995). The shif ts in resource availability and
diversity, and changes in the physical aspects of t he environment, associated with land transformation reduce the ability for resource-spec ialized organisms, including speciesrich groups such as the beetles (Coleoptera). Land conversion may potentially alter the diversity of resources available to beetles with na rrow niches and in turn may shift local Coleopteran composition. It has been hypothesized t hat a more diverse pool of resources supports a more diverse community of consumers (Bro se 2003). The potential availability of these natural resources in habitats may be limit ing factors in Coleopteran diversity, richness and abundance. The insect order Coleoptera (beetles) is the large st of all taxa on the planet, containing approximately 400,000 described species and about 25% of all described organisms on Earth (Hanson 2000). Beetles can be fo und in terrestrial or even aquatic habitats, including in or upon leaf litter, canopy or understory vegetation, flowers, fruits, fungus and decaying logs (Solis 1999). Collectivel y, beetles have a wide variety of dietary habits: fungivory, predation, saprophagy, f rugivory and phytophagy are a few examples (Hanson 2000). Hence Coleopteran community composition and richness may be correlated to alteration in the diversity and ab undance of biological resources associated with environmental disturbances. Studies in Sabah, Malaysia, comparing primary fore st, logged forest, and plantations indicated that the species richness, ab undance and composition of subterranean beetles correlated with amount of leaf litter (Chung et al. 2000). These studies also showed that sapling densities and plan t species richness correlated with the composition, abundance and species richness of unde rstory beetles. The magnitude of canopy cover was correlated with the presence of ar boreal Coleopterans (Chung et al. 2000). Other studies found the diversity and abunda nce of many invertebrates on agricultural lands have been threatened by exhausti ve farming practices (Carcamo et al. 1995) Rove beetles (Staphylinidae) and ground beetl es (Carabidae) that prey on crop pests and are food for many members of higher troph ic levels (Holland, 2007) were studied for the effects on diversity, species richn ess and abundance in relation to soil moisture levels on farmland. They found that soil m oisture levels during the previous winter and summer were related to the oviposition s election by female beetles (Holland, 2007). Availability of natural resources like water amongst others, may be limiting factors in Coleopteran habitation. These studies ar e significant in that they suggest that beetle species richness, diversity and abundance ar e influenced by the abundance and distribution of available resources. However, ther e is a lack of information regarding how habitat disturbance correlates with resource av ailability and how these factors may affect Coleopteran habitation. This study examined the relationship between habit at disturbance and Coleopteran diversity in three habitats in La Cruz, Costa Rica: primary forest, secondary forest and pasture. Each habitat corresponds to a d ifferent level of disturbance, with primary forest being undisturbed, secondary forest being moderately disturbed and pastureland being highly disturbed. I hypothesized that the level of habitat disturbance correlates with the level of natural resource diver sity, habitats that offer a wider variety of resources, e.g. fruit, fungus or detritus ought to potentially sustain an overall greater diversity of Coleopterans. It has been shown that i nsects are prevalent and vital elements within ecosystems (Janzen, 1987) that noticeably re act to environmental alterations. Thus they potentially may be used as valid indicators of habitat conditions (Chung et al. 2000).
MATERIALS AND METHODS Study Sites Coleopterans were collected in three different habi tats in La Cruz, Costa Rica: pastureland, primary forest and secondary forest. A ll three habitats were located on a privately-owned of land at approximately 1440 m in elevation. Habitats were in close proximity to one another, with pasture adjacent to secondary forest and secondary forest adjacent to primary forest. This created a habitat disturbance gradient. The pasture was actively grazed and was primarily comprised of tall grass. The secondary forest was relatively young, with an abundance of small trees and herbaceous understory plants whereas the primary forest was primarily made up of large canopy trees and scattered herbaceous understory. Collecting Methods Collection took place within 300 m2 transects in each microhabitat. Transect sites were surveyed seven times over the course of a three-wee k period between mid-April and the beginning of May. Three methods of collection were used: hand-collecting, beating the vegetation and sweep-netting. Beetles were collecte d for 1 hour in each site for 7 days. A sweep net was used to collect fallen specimens afte r plant matter was beaten with a wooden pole. Specimens captured within sweep-net we re incrementally collected and placed in habitat specific collecting vials filled with ethanol. Ethanol served in killing and preserving specimens. Sweep-netting took place when it optimized collecting efficiency, generally being applied in the pasture and secondar y forest where herbaceous plant matter was more abundant. These samples were also p laced in habitat specific collecting vials filled with ethanol. Hand collecting occurred during beating and sweep-netting collection. Hand-collected samples were also placed in ethanol filled collecting vials that were habitat specific. Sorting and Identification Specimens were kept in collecting vials that were l abeled with habitat site and day of collection. Samples were then sorted into morpho-sp ecies according to family using a family reference guide and a dissecting microscope. If the family of a particular specimen could not be identified then it was placed in categ ory called Unknown. Statistical Analysis Samples were sorted to family level and identified to morpho-species. Species richness, evenness and diversity indices were calculated for morpho-species. Differences in Shannon-Weiner diversity index between all habitats were then compared using a modified t-test. Species richness, evenness and div ersity were then calculated at the
family level to indicate family composition within habitats. There were no modified ttests performed comparing family diversity between habitats. RESULTS A total of 865 beetles were collected, of which 125 morpho-species were identified along with 22 families. Species richness was found to be highest in primary forest habitats followed by secondary forest and then pasture (Figu re 1). Diversity for the primary forest was greater than for either the pasture (modified t -test, t = 9.74, P < 0.001) or secondary forest (modified t-test, t = 2.43, 0.02 < P < 0.05) Secondary forest had greater diversity than pasture (Modified t-test = 6.76, 0.001< P < 0. 05) The Margalefs diversity index for the primary forest was higher than for secondary fo rest, and pasture had the lowest diversity (Figure 1c). Pasture had a greater evenne ss than primary forest or secondary forest (Figure 1d). Comparison of family composition indices indicated that family richness was highest in the secondary forest and that both prima ry and secondary forest had greater family richness than pasture (Figure 2a). Diversity was highest in primary forest followed by secondary forest, and then pasture (Figure 2c). The Margalefs index of diversity increased going from pasture to secondary forest an d was greatest in primary forest (Figure 2b). Family evenness was higher in primary forest than in either secondary forest or pasture (Figure 2d). There was noticeable turnover between the pasture and the primary forest, with Ptilyodactilidae, Monotomidae, Carabidae, Lycidae a nd Scarabaeidae only found in the primary forest, whereas Staphylinidae, Brentidae an d Coccinelidae were only found in the pasture. Between the pasture and secondary fore st there was also turnover, with Passalidae and Coccinelidae only present in the pas ture. The secondary forest had Ptilodactylidae, Cantharidae, Lycidae and Languriid ae whereas the pasture did not have these families present. There was less turnover bet ween the primary forest and the secondary forest, with Buprestidae and Mordelidae o nly found in the primary forest and Cerambycidae only found in the secondary forest. DISCUSSION The results here show that coleopteran species and family diversity differ significantly across a disturbance gradient. These differences ma y be due to reduction in the diversity may be correlated to the diversity or abundance of natural resources caused by conversion of forest to pastureland. Primary forest had the greatest morpho-species richness and diversity, indicating that forest syst ems can harbor more complex Coleopteran community by providing resource and mic rohabitat variation. In addition, the species and family composition, and the trophic levels, of beetle communities present changed dramatically between habitats, which may mi rror resource and microhabitat availability. Niche diversity as inferred from spec ies diversity, however, does not necessarily correlate with diversity of resource ty pes, as many of the mopho-species may have been dependent upon exclusive resources; e.g. only herbaceous plant matter, only
fungus, etc. Beetle species that are part of the sa me guild are primarily dependent upon similar resource types and therefore may not be goo d indicators of overall resource diversity. Feeding guild diversity may be reflected by beetle family diversity, since many families are characterized by what they eat. The re sults here of the analyses of familylevel diversity show that primary forests harbor a greater diversity and this likely to be related to the variety of available foods. Collecti vely, beetle families possess a wide variety niches that fall into numerous feeding guil ds, specialized on certain resources. For instance, the family Chrysomelidae feeds primarily on the foliage of herbaceous plants (Solis 1999). The family Curculionidae primarily f eeds on various live plant matter, including leaves, seeds, fruits, stems, wood, flowe rs, etc. (Solis 1999). Other families such as the Carabidae, are characterized by being v ery predatory, feeding on small insects on the forest floor (Solis 1999). Studies done in Yucatan, Mexico found that agricu ltural lands possessed significantly fewer beetle families than in primary dry forest (Goode 2003). This supports the concept that areas with low resource variation possess a low numbers of Coleopteran families. Agricultural lands are primarily made up of uniform vegetation and lack variable ground microclimates that would be conduci ve to terrestrial Coleopteran feeding guilds. Other studies done with dung and carrion be etles found that forest fragmentation drastically reduced mammal and bird populations. Ma mmals and birds produce wastes that carrion and dung beetles feed upon and are the refore limiting resources for these beetles. Fragmentation indirectly resulted in the r eduction of dung and carrion beetle populations (Klein 1989). Differences in beetle family diversity across habi tats reflect differences in resource diversity and abundance. The great abundan ce of Chrysomelids in the primary forest can be explained by the higher abundance of plant material on which they feed, independent of the diversity of plants they use. Pt ilodactylids, which are generally saprophageous, were highly abundant in the primary forest because of the great availability of rotting material. Carabid abundance was higher in the primary forest and secondary forest presumably on account of the leaf litter and ground cover abundance. The forest had a higher family diversity and family richness, which implicated greater resource diversity than in either the secondary for est or the pasture. The abundance of smaller trees and herbaceous plant matter in the se condary forest resulted in a high abundance of Curculionids. Family diversity and ric hness was moderate in the secondary forest indicating that resource diversity was highe r than in the pasture but lower than in the forest. The pasture had a limited amount of veg etation, which was mainly tall grass. Thus there was a high abundance of phytophageous Ch rysomelids who were feeding on the abundant grasses. The pasture also had a high a bundance of Coccinelids, which typically are predators of small insects (Solis 199 9) that were highly abundant in pasture. Diversity of resources proved to be lowest in the p asture as there was less family diversity and family richness. Turnover of families within habitats along a distu rbance gradient suggest that certain resources may be exclusive to certain habit ats. The presence of Ptilodactylidae in the primary forest and secondary forest suggests th at there is a relatively high abundance of decaying matter available in relation to in the pasture. Coccinelidae only being present in the pasture indicates that there may be a greate r abundance of prey items that are
potentially excluded from the secondary forest and primary forest. Not all turnover seems to be significant, as many families that were found in a particular habitat, such as Languriidae in the secondary forest, only had a few individuals that may have only been present due to environmental stochasiticity. Famili es with such low abundance may have been an anomaly in a given habitat, thus such minim al turnover may not be a good representation of the families local composition. The study shows that Coleopteran species and famil y diversity within habitats proved to correlate with levels of habitat disturba nce. Decreased landscape heterogeneity, reduced habitat diversity and increased land use th reaten biodiversity (Hendrickx 2007). Habitat disturbance associated with human land tran sformation causes forest fragmentation. Fragmentation causes changes in the biodiversity that shift resource diversity and abundance (Klein 1989). Coleopteran c ommunities are significantly altered by these changes, as limitations in certain resourc es can prevent certain beetle guilds and or families from inhabiting affected areas. While t his study offered significant results indicating that diversity differed between habitats Coleopterans were only sampled from the understory level and no canopy level diversity was taken into account. The primary forest most likely possess high diversity and abund ance at the canopy level, whereas in the secondary forest and pasture the canopy would n ot be as significant. Additionally, because Coleoptera is such a large and diverse orde r of insects, there is little information regarding their ecological resilience of beetle com munities. Future studies could look at how Coleopteran diversity and abundance changes in the periods immediately after forest fragmentation, to determine the following patterns of community turnover. ACKNOWLEDGEMENTS Firstly I would like to thank Karen Masters for hel ping me develop my project and organizing my ideas. I couldnt have done it with o ut her help. I would also like to thank James Wolfe for allowing me to do my sampling on hi s land in La Cruz. It would have been very difficult to find an appropriate study si te without his generosity. Pablo Allen also helped me a lot, whether it was with statistic ally analyzing my data or with helping me identify collected Coleopteran families. The sor ting process would have been a lot longer without his expertise. I also cant forget t o thank Taegan, who helped me understand and produce numerous graphs. I also tha nk Cyrus Harp, Kevin Clifford and Katelyn Burgess for proofreading and helping correc t my paper. LITERATURE CITED Brose, U. 2003. Bottom-up control of Carabid beetle communities in early successional wetlands: mediated by vegetation structure or plan t diversity? Springer-Verlag, OecologiaChem Soc 135 Crcamo, H.A., Niemala, J.K. & Spence, J.R. 1995. F arming and ground beetles: effects of agronomic practice on populations and community structure. Canadian Entomologist 127:123-140.
Chung, A.Y.C, Eggelton P., Speight, M. R., Hammond, P.M., Chey, V.K. The diversity of beetle assemblages in different habitat types i n Sabah, Malaysia, Bulletin of Entomological Research 90: 475-96 Goode, James S., P. Mckeown,. 2003. A List of Coleo pteran Families Found in Disturbed and Undisturbed Areas in Yucatan, Mexico Journal of the Mississippi Academy of Sciences Hanson, Paul. 2000, in Monteverde: ecology and cons ervation of a tropical cloud forest, Nalini M. Nadakarni, New York Oxford Press Hendrickx, Frederik., J.P Maelfait, W.V Wingerden, O. Schweiger, M. Speelmans, S. Aviron, I. Augenstein, R. Billeter, D. Bailey, R. Bukacek, F. Burel, T. Diekotter, J. Dirksen, F. Herzog, J. Liira, M. Roubalova (200 7). How landscape structure, land-use intensity and habitat diversity affect co mponents of total arthropod diversity in agricultural landscapes. Journal of A pplied Ecology 44: 340-351 Holland, J.M. Barkett, Thomas T. Southway, S. 2007. Spatio-temporal distribution and emergence of beetles in arable fields in relation to soil moisture. Bulletin of Entomological Research 97 no1 89-100 Janzen, D.H. 1987. Insect diversity of a Costa Rica n dry forest: why keep it, and how? Biological Journal of the Linnean Society 30, 343356. Klein, Bertt C. 1989. Effects of Forest Fragmentati on on Dung and Carrion Beetle Communities in Central Amazonia. Ecology 70:1715-1 725 McNeely, J.A., Gadgil, M., Leveque, C., Padoch, C. & Redford, K. 1995. Human Influences on biodiversity. pp. 711-822 in Heywood V.H. & Watson, R.T. (Eds) Global biodiversity assessment. UNEP, Cambridge, C ambridge University Press. Solis, Angel. 1999. Costa Rican beetles: the most c ommon families, Instituto Nacional de Biodiversidad
FIGURE 2 Beetle community diversity and richness parameter s for pastureland, secondary forest, and primary forest at La Cruz, Co sta Rica. a) Number of individuals vs. habitat types, b) Species richness vs. habitat type s, c) Margalefs index vs. habitat types, d) Evenness vs. habitat types, e) Shannon-Weiner Di versity Index vs. habitat types nrrrnrn n nrrrnrn n nrrrnrn n nrrrnrn na) b) e) c) d) nrrrnrn n
FIGURE 2. Coleopteran family diversity and richness across three habitats of variable disturbance. Results show that species richness is highest in the secondary forest, while diversity is highest in the primary fores. a) Speci es richness vs. habitat type, b) Margelefs index vs. habitat type, c) Shannon-Weine r Index vs. habitat type, and (d) Evenness vs. habitat type a) c) d) b) nrrrnrn n nrrrnrn n nrrrnrn n nrrrnrn n
FIGURE 3. Percentatge of beetle families found in p asture had a high percentage of Chrysomelidae. Secondary forest had a high percenta ge of Curculionidae. Primary forest had a high percentage of Ptilodactylidae and Chryso melidae. a) Secondary Forest family composition, b) Primary Forest family composition c ) Pasture family composition. nr !r r!r r"r #r "r $"nrr $r %&r %'r %r (nr (r""r n"n"r r"r !rr nr &rnr nr !r r!r r"r #r "r $"nrr %&r %'r %r "r n"n"r !rr )*+a) b) c) rnr nr !r r!r r"r "r $"nrr %&r "r r"r nr n&"r )*+
nr rnr &rnr nr !r r!r r"r #r "r $"nrr $r %&r %'r %r (nr (r""r "r n"n"r r"r !rr nr n&"r )*+ rnnr nr rrn rn FIGURE 4. The number of individuals found for each family in three habitats of variable disturbance. Chrysomelids dominate pasture whereas Ptilodactylids dominate primary forest and Curculionids dominate secondary forest.
APENDIX 1.The number of individuals found per morph o-species totals for pasture, secondary forest and primary forest. nn n nn n n,-!"* n, rn,rn, &r,n,n, n, !,!, !, "rr" r!,r!, r, r, r",r",/ r", r",0 r",$/ r", r",/. ,!rn' 12,3 ,!"'n ,"4 ,*! ,%/5 r",6 r",7 r",8 r",9 r",% r",( r",:.'n r",4.+&* r", r",;.! ,+!"r&n
,r ,<"n ,!"n ,2,/ ,2,= ,2,= ,+!"&n ,+nr ,+"' ,+&nr ,",",. ",!"'+ ",!"+n ", ",0.5 ",$.5 ", ",/ ",6 ",7 ",8.! ",9.!! ",%!'!"* ",(!"* ",&*' ","! ",!!&n $"nr,$"nr, $"nr,!""' $"nr,!"""' $"nr,!r"" $"nr, $"nr,0 $"nr,$ $"nr, $"nr,/ $"nr,6 $"nr,7 $"nr,8 $"nr,9 $"nr,% $,-! %&,%&, %&,
%&,0 %&,$ %&, %',%', %,(n,(r"," n",n", =r !,!,''r !,r n,n&,-. n&, )*,,n+n )*+ )*+ )*+ )*+ )*+ )*+ )*+ )*+' )*+, )*+, )*+,.<>>&n )*+,,+nr&n )*+,'r&n )*+,!"* )*+,, )*+, )*+,"n )*+,nrr! )*+
APENDIX 2. The number of individuals per Coleoptera n family in three habitat types. The pasture possessed a high abundance of Chrysomel ids. Secondary forest possessed a high abundance of Curculionids. Primary forest poss essed a high abundance of Ptilodactylids and Chrysomelids. nr r rn rn nr rnr &rnr nr !r r!r r"r #r "r $"nrr $r %&r %'r %r (nr (r""r"r n"n"r r"r !rrnr n&"r )*+