Insect Colonization of Exotic and Native Trees and …iufro-archive.boku.ac.at/nz/gomez_p.pdftrees...
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Number of Species 0 100 200 300 400 500 15Complete Data Sets Al Pairs Coleoptera Diptera Hemiptera Homoptera Hymenoptera Lepidoptera Macro - lepidotera = Outliers * = Significant difference * * * * Insect Colonization of Exotic and Native Trees and Shrubs TOM DEGOMEZ and MICHAEL R. WAGNER Introduction For as long as humans have been cultivating plants and exploring new ecosystems they have been utilizing exotics. Among these exotic plants are potato, cotton, wheat, sugarcane, apples, cacao, oak, rose, and teak, to name but a few. There are examples of exotic plants causing more problems than benefits but the number of beneficial exotic plants is overwhelming. These failures have brought an air of caution to the use of exotics and particularly exotic trees in plantations. One of the cited reasons for not introducing exotic trees is that native insect populations will attack them more heavily than native trees. There has been substantial, but conflicting, research on the factors that influence the colonization of insects on exotic host trees (Strong, 1974 a,b,c; Southwood, 1960 a, b; Kennedy and Southwood, 1984; Lawton & Schroder, 1977; Neuvonen & Niemela, 1981; Connor et al., 1980; Moran & Southwood, 1982). However, the developing theory that attempts to explain the structure and dynamics of the roles of forest insects on host plants and within host plant communities is helping to define the theory of plant herbivore interactions. This study adds additional information to the development of the host plant insect interaction theory by providing an analysis of insect species data sets that describe the number of species of insects that occur on 26 tree and shrub taxa in their native range and a like data set from an exotic location. Some of the pairs consist of two plants from the same genus rather than the same species. We correlated the arthropod species number and the dates that the plants were introduced to their exotic range, for 24 taxa. For 25 taxa we compared the physical range covered in their native and exotic lands with the number of arthropods colonizing the taxa. Results 1. There was a significant difference in the average number of insect species when the data sets for ‘15 complete data sets’ and ‘all pairs’ were tested. An average of 189 and 14.5 insect species on native plants grown in their native habitat and 60 and 6 (respectively) when grown in the exotic habitat (Figure 1). 2. When the ratio of matched pairs of exotic and native arthropod species numbers are plotted against the number of years from exotic introduction to the arthropod data set collection the linear regression analysis is nonsignificant (Figure 2). 3. When the number of arthropods on native plants are plotted against the area that the plant covers in its native range the linear and polynomial regression is nonsignificant (Figure 3). Discussion •The results indicate that there are more arthropods on native than exotic plants which is supported by previous work (Southwood, 1960a,b; Strong, 1974a,b,c; Kennedy and Southwood, 1984). •The study fails to support Southwood’s (1960a,b) theory that evolutionary time determines insect colonization rates. No evidence exists in this study to support or reject that geologic time influences colonization rates. •The nonsignificant linear and polynomial regression analysis of native plant arthropod numbers when compared to area indicates that arthropod colonization on native plants may be at a state of equilibrium. The nonsignificant linear and polynomial regression analysis of exotic plant arthropod numbers when compared to area does not support our hypothesis that the area on which an exotic is grown influences the rate at which insects colonize new host plants. Conclusion Greater inherent arthropod populations on native trees and shrubs indicate that exotic tree plantations will generally have less damage from insects than native trees. Furthermore, we would caution that proper field-testing is always essential prior to the establishment of exotic plantations. We believe many misinterpretations have occurred regarding the susceptibility of exotic tree species because the tree was planted on a site that it was not adapted to. = Location of exotics. = Location of natives. Methods The data base was generated by conducting a search of computer databases, reference sections of papers, and personal contact with insect and plant workers. Each data set in the analysis had to meet a strict set of criteria to be included. The data set consists of 32 pairs of data sets from 18 published papers, one paper in press, and one unpublished research report. From these data sets we analyzed the original 32 data sets as a group, 15 pairs of data sets that represented complete collections of all arthropods or all insects, and 85 pairs that represent seven individual insect orders or suborders. These were analyzed using a Wilcoxson Signed Rank Sum Test and the Sequential Bonneferroni analysis. Dates of introduction for 25 taxa were found in 12 published papers and one paper in press. (Note: The date of introduction for Larrea Cav. (Covillea) was not included due to a 3,000 year variability in its introduction date.) Area of cover is from 11 published papers, two personal contacts, a GIS analysis conducted at N. Arizona Univ., and from estimations made from maps by Olckers and Hulley (1991) and T. Olkers (personal contact). The area of cover data is for the region from which the arthropod data sets were collected and not worldwide area. Separate regression analysis was conducted on the number of years from introduction to the date the arthropods were collected and the area of cover in relation to the number of arthropod species in each group. Bibliography Kennedy, C.E.J., and T.R.E. Southwood. 1984. The number of species of insects associated with British tress: A re-analysis. Journal of Ecology 53: 455-478. Lawton, J.H. & D. Schroder. 1977. Effects of plant type, size of geographical range and taxonomic isolation on number of insect species associated with British plants. Nature 265:37-40. Moran, V.C. & T.R.E. Southwood. 1982. The guild composition of arthropod communities in trees, Journal of Animal Ecology 51:289-306. Neuvonen, S. & P. Niemela. 1981. Species richness of macrolepidoptera on Finnish decidous trees and shrubs. Oceologia (Berl) 51:364-370 Olkers, T., and P.E. Hulley. 1991. Impoverished insect herbivore faunas on the exotic weed Solanum mauritianum Scop. and relative to indigenous Solanum species in Natal/KwaZulu and Transkei. Ent. Soc. S. Af. 54: 39-50. Southwood, T.R.E. 1960a. The number of species of insects associated with various trees. Journal of Animal Ecology 30:1-8. Southwood, T.R.E. 1960b. The abundance of the Hawaiian trees and the number of their associated insect species. Proc. of the Hawaiian Entomological Society 17:299-303. Southwood, T.R.E., V.C. Moran, & C.E.J. Kennedy. 1982. The richness, abundance and biomass of the arthropod communities on trees. Journal of Animal Ecology 51:635- 649. Strong, D.R., Jr. 1974a. The insects of British trees and non-asymptotic models of species diversity. Proc. of the Missouri Botanical Garden. Strong, D.R., Jr. 1974b. Rapid asymptotic species accumulation in phyto- phagous insect communities: the pests of cacao. Science 185:1064-1066. Strong, D.R., Jr. 1974c. Nonasymptotic species richness models and the insects of British trees. Proc. Nat. Acad. Sci. 71(7): 2766-2769. Native Robinia in northern Arizona Exotic Robinia in northern Arizona 0.573 0.089 0.393 0.057 Macro-lepidoptera 0.773 0.056 0.568 0.034 Lepidoptera 0.284 0.716 0.517 0.152 Hymenoptera 0.321 0.203 0.656 0.019 Homoptera 0.483 0.166 0.530 0.045 Hemiptera 0.649 0.116 0.418 0.084 Diptera 0.187 0.263 0.177 0.063 Coleoptera 0.489 0.122 0.574 0.027 15 Complete sets 0.728 0.008 0.637 0.003* All orders P r 2 P r 2 Quadratic Linear Arthropod Group *Bold values represent negative response to the linear test. 0.550 0.113 0.005 0.593 0.432 0.057 0.137 0.162 Macro-lepidoptera 0.157 0.603 0.923 0.120 0.376 0.159 0.814 0.006 Lepidoptera 0.346 0.881 0.601 0.395 0.977 0.000 0.411 0.233 Hymenoptera 0.001 0.941 0.609 0.132 0.776 0.015 0.127 0.023 Homoptera 0.566 0.315 0.361 0.335 0.649 0.057 0.296 0.179 Hemiptera 0.543 0.210 0.867 0.091 0.553 0.062 0.399 0.182 Diptera 0.053 0.692 0.371 0.246 0.087 0.411 0.908 0.001 Coleoptera 0.665 0.127 0.176 0.356 0.824 0.007 0.312 0.085* 15 Complete sets 0.110 0.084 0.088 0.055 0.824 0.001 0.428 0.009 All orders P r 2 P r 2 P r 2 P r 2 Native habitat Exotic habitat Native habitat Exotic habitat Quadratic Linear Arthropod Group Figure 1. Mean number of species by insect order when grown in native & exotic habitats. Figure 2. Regression analysis of the ratio of arthropod species and date of introduction into exotic range. Figure 2. Regression analysis of Arthropod species and area of range in native and exotic habitats. *Bold values represent negative response to the linear test. University of Arizona School of Natural Resources Northern Arizona University Flagstaff, Arizona 86011 U.S.A. [email protected] School of Forestry Northern Arizona University Flagstaff, Arizona 86011 U.S.A. [email protected]
Transcript of Insect Colonization of Exotic and Native Trees and …iufro-archive.boku.ac.at/nz/gomez_p.pdftrees...
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Insect Colonization of Exotic and Native Trees and ShrubsTOM DEGOMEZ and MICHAEL R. WAGNER
IntroductionFor as long as humans have been cultivating plants
and exploring new ecosystems they have been utilizingexotics. Among these exotic plants are potato, cotton,wheat, sugarcane, apples, cacao, oak, rose, and teak, toname but a few. There are examples of exotic plants causing more problems than benefits but the number of beneficial exotic plants is overwhelming. These failures have brought an air of caution to the use of exotics and particularly exotic trees in plantations. One of the cited reasons for not introducing exotic trees is that nativeinsect populations will attack them more heavily thannative trees.
There has been substantial, but conflicting, research on the factors that influence the colonization of insects on exotic host trees (Strong, 1974 a,b,c; Southwood, 1960 a, b; Kennedy and Southwood, 1984; Lawton & Schroder,1977; Neuvonen & Niemela, 1981; Connor et al., 1980;Moran & Southwood, 1982). However, the developing theory that attempts to explain the structure and dynamics of the roles of forest insects on host plants and within host plant communities is helping to define the theory of plant herbivore interactions. This study adds additional information to the development of the host plant insect interaction theory by providing an analysis of insect species data sets that describe the number of species of insects that occur on 26 tree and shrub taxa in their native range and a like data set from an exotic location. Some of the pairs consist of two plants from the same genus rather than the same species. We correlated the arthropod species number and the dates that the plants were introduced to their exotic range, for 24 taxa. For 25 taxa we comparedthe physical range covered in their native and exotic lands with the number of arthropods colonizing the taxa.
Results 1. There was a significant difference in the average number of insect species when the data sets for ‘15 complete data sets’ and ‘all pairs’ were tested. An average of 189 and 14.5 insect species on native plants grown in their native habitat and 60 and 6 (respectively) when grown in the exotic habitat (Figure 1).
2. When the ratio of matched pairs of exotic and native arthropod species numbers are plotted against the number of years from exotic introduction to the arthropoddata set collection the linear regression analysis is nonsignificant (Figure 2).
3. When the number of arthropods on native plants are plotted against the area that the plant covers in its native range the linear and polynomial regression is nonsignificant (Figure 3).
Discussion
•The results indicate that there are more arthropods on native than exotic plants which is supported by previous work (Southwood, 1960a,b; Strong, 1974a,b,c; Kennedy and Southwood, 1984).
•The study fails to support Southwood’s (1960a,b) theory that evolutionary time determines insect colonization rates. No evidence exists in this study to support or reject that geologic time influences colonization rates.
•The nonsignificant linear and polynomial regression analysis of native plant arthropod numbers when compared to area indicates that arthropod colonization on native plants may be at a state of equilibrium. The nonsignificantlinear and polynomial regression analysis of exotic plant arthropod numbers when compared to area does not support our hypothesis that the area on which an exotic is grown influences the rate at which insects colonize new host plants.
Conclusion
Greater inherent arthropod populations on native trees and shrubs indicate that exotic tree plantations will generally have less damage from insects than native trees.
Furthermore, we would caution that proper field-testing is always essential prior to the establishment of exotic plantations. We believe many misinterpretations have occurred regarding the susceptibility of exotic tree species because the tree was planted on a site that it was not adapted to.
= Location of exotics.
= Location of natives.
MethodsThe data base was generated by conducting a search of
computer databases, reference sections of papers, and personal contact with insect and plant workers. Each data set inthe analysis had to meet a strict set of criteria to be included.
The data set consists of 32 pairs of data sets from 18 published papers, one paper in press, and one unpublished research report. From these data sets we analyzed the original 32 data sets as a group, 15 pairs of data sets that represented complete collections of all arthropods or all insects, and 85 pairs that represent seven individual insect orders or suborders. These were analyzed using a Wilcoxson Signed Rank Sum Test and the Sequential Bonneferroni analysis.
Dates of introduction for 25 taxa were found in 12 published papers and one paper in press. (Note: The date of introduction for Larrea Cav. (Covillea) was not included due to a 3,000 year variability in its introduction date.)
Area of cover is from 11 published papers, two personal contacts, a GIS analysis conducted at N. Arizona Univ., and from estimations made from maps by Olckers and Hulley (1991) and T. Olkers (personal contact). The area of cover data is for the region from which the arthropod data sets were collected and not worldwide area.
Separate regression analysis was conducted on the number of years from introduction to the date the arthropods were collected and the area of cover in relation to the number of arthropod species in each group.
BibliographyKennedy, C.E.J., and T.R.E. Southwood. 1984. The number of species of insects
associated with British tress: A re-analysis. Journal of Ecology 53: 455-478.Lawton, J.H. & D. Schroder. 1977. Effects of plant type, size of geographical
range and taxonomic isolation on number of insect species associated withBritish plants. Nature 265:37-40.
Moran, V.C. & T.R.E. Southwood. 1982. The guild composition of arthropod communities in trees, Journal of Animal Ecology 51:289-306.
Neuvonen, S. & P. Niemela. 1981. Species richness of macrolepidoptera on Finnish decidous trees and shrubs. Oceologia (Berl) 51:364-370
Olkers, T., and P.E. Hulley. 1991. Impoverished insect herbivore faunas on theexotic weed Solanum mauritianum Scop. and relative to indigenous Solanum species in Natal/KwaZulu and Transkei. Ent. Soc. S. Af. 54: 39-50.
Southwood, T.R.E. 1960a. The number of species of insects associated with various trees. Journal of Animal Ecology 30:1-8.
Southwood, T.R.E. 1960b. The abundance of the Hawaiian trees and the number of their associated insect species. Proc. of the Hawaiian Entomological Society 17:299-303.
Southwood, T.R.E., V.C. Moran, & C.E.J. Kennedy. 1982. The richness, abundance and biomass of the arthropod communities on trees. Journal of Animal Ecology 51:635- 649.
Strong, D.R., Jr. 1974a. The insects of British trees and non-asymptotic modelsof species diversity. Proc. of the Missouri Botanical Garden.
Strong, D.R., Jr. 1974b. Rapid asymptotic species accumulation in phyto-phagous insect communities: the pests of cacao. Science 185:1064-1066.
Strong, D.R., Jr. 1974c. Nonasymptotic species richness models and the insectsof British trees. Proc. Nat. Acad. Sci. 71(7): 2766-2769.
Native Robinia in northern Arizona Exotic Robinia in northern Arizona
0.5730.0890.3930.057Macro-lepidoptera
0.7730.0560.5680.034Lepidoptera
0.2840.7160.5170.152Hymenoptera
0.3210.2030.6560.019Homoptera
0.4830.1660.5300.045Hemiptera
0.6490.1160.4180.084Diptera
0.1870.2630.1770.063Coleoptera
0.4890.1220.5740.02715 Complete sets
0.7280.0080.6370.003*All orders
Pr2Pr2
QuadraticLinearArthropod Group
*Bold values represent negative response to the linear test.
0.5500.1130.0050.5930.4320.0570.1370.162Macro-lepidoptera
0.1570.6030.9230.1200.3760.1590.8140.006Lepidoptera
0.3460.8810.6010.3950.9770.0000.4110.233Hymenoptera
0.0010.9410.6090.1320.7760.0150.1270.023Homoptera
0.5660.3150.3610.3350.6490.0570.2960.179Hemiptera
0.5430.2100.8670.0910.5530.0620.3990.182Diptera
0.0530.6920.3710.2460.0870.4110.9080.001Coleoptera
0.6650.1270.1760.3560.8240.0070.3120.085*15 Complete sets
0.1100.0840.0880.0550.8240.0010.4280.009All orders
Pr2Pr2Pr2Pr2
Native habitatExotic habitatNative habitatExotic habitat
QuadraticLinearArthropod Group
Figure 1. Mean number of species byinsect order when grown in native & exotic habitats.
Figure 2. Regression analysis of the ratio of arthropod species and date of introduction into exotic range.
Figure 2. Regression analysis of Arthropod species and area of range in native and exotic habitats.
*Bold values represent negative response to the linear test.
University of ArizonaSchool of Natural Resources Northern Arizona University
Flagstaff, Arizona 86011 [email protected]
School of ForestryNorthern Arizona University
Flagstaff, Arizona 86011 [email protected]
Exotic Robinia in northern Arizona
