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Animals (Insects - Butterflies) -- Summary
How will earth's butterflies respond to the twin evils of the climate-alarmist crowd, i.e., atmospheric CO2 enrichment and global warming? We here explore what has been learned about the question over the past few years, beginning with a review of studies that focus on carbon dioxide and concluding with studies that focus on temperature.

In a study of Lotus corniculatus (a cyanogenic plant that produces foliar cyanoglycosides to deter against herbivory by insects) and the Common Blue Butterfly (Polyommatus icarus, which regularly feeds upon L. corniculatus because it possesses an enzyme that detoxifies cyanide-containing defensive compounds), Goverde et al. (1999) collected four genotypes of L. corniculatus differing in their concentrations of cyanoglycosides and tannins (another group of defensive compounds) near Paris, France. They then grew them in controlled-environment chambers maintained at atmospheric CO2 concentrations of 350 and 700 ppm, after which they determined the effects of the doubled CO2 concentration on leaf quality and allowed the larvae of the Common Blue Butterfly to feed upon the plants' leaves. This work revealed that elevated CO2 significantly increased leaf tannin and starch contents in a genotypically-dependent and -independent manner, respectively, while decreasing leaf cyanoglycoside contents independent of genotype. These CO2-induced changes in leaf chemistry increased leaf palatability, as indicated by greater dry weight consumption of CO2-enriched leaves by butterfly larvae. In addition, the increased consumption of CO2-enriched leaves led to greater larval biomass and shorter larval development times, positively influencing the larvae of the Common Blue Butterfly. Hence, it is not surprising that larval mortality was lower when feeding upon CO2-enriched as opposed to ambiently-grown leaves.

Goverde et al. (2004) grew L. corniculatus plants once again, this time from seed in tubes recessed into the ground under natural conditions in a nutrient-poor calcareous grassland, where an extra 232 ppm of CO2 was supplied to them via a Screen-Aided CO2 Control (SACC) system (Leadley et al., 1997, 1999), and where insect larvae were allowed to feed on the plants (half of which received extra phosphorus fertilizer) for the final month of the experiment. Information gleaned from following these procedures indicated that the atmospheric CO2 enrichment employed in this experiment increased the total dry weight of plants growing on the unfertilized soil by 21.5% and that of plants growing on the phosphorus-enriched soil by 36.3%. However, the elevated CO2 treatment had no effect on pupal and adult insect mass, although Goverde et al. report there were "genotype-specific responses in the development time of P. icarus to elevated CO2 conditions," with larvae originating from different mothers developing better under either elevated CO2 or ambient CO2, while for still others the air's CO2 concentration had no effect on development.

In another study by some of the same team of researchers, Goverde et al. (2002) raised larvae of the satyrid butterfly (Coenonympha pamphilus) in semi-natural undisturbed calcareous grassland plots exposed to atmospheric CO2 concentrations of 370 and 600 ppm for five growing seasons. In doing so, they found that the elevated CO2 concentration increased foliar concentrations of total nonstructural carbohydrates and condensed tannins in the grassland plants; but in what is often considered a negative impact, they found that it also decreased foliar nitrogen concentrations. Nevertheless, this phenomenon had no discernible impact on butterfly growth and performance. Larval development time, for example, was not affected by elevated CO2, nor was adult dry mass. In fact, the elevated CO2 increased lipid concentrations in adult male butterflies by nearly 14%, while it marginally increased the number of eggs in female butterflies. The former of these responses is especially important, because lipids are used as energy resources in these and other butterflies, while increased egg numbers in females also suggests an increase in fitness.

Turning to the study of temperature effects on butterflies, Parmesan et al. (1999) analyzed distributional changes over the past century of non-migratory species whose northern boundaries were in northern Europe (52 species) and whose southern boundaries were in southern Europe or northern Africa (40 species). This work revealed that the northern boundaries of the first group shifted northward for 65% of them, remained stable for 34%, and shifted southward for 2%, while the southern boundaries of the second group shifted northward for 22% of them, remained stable for 72%, and shifted southward for 5%, such that "nearly all northward shifts involved extensions at the northern boundary with the southern boundary remaining stable."

This behavior is precisely what we would expect to see if the butterflies were responding to shifts in the ranges of the plants upon which they depend for their sustenance, because increases in atmospheric CO2 concentration tend to ameliorate the effects of heat stress in plants and induce an upward shift in the temperature at which they function optimally. These phenomena tend to cancel the impetus for poleward migration at the warm edge of a plant's territorial range, yet they continue to provide the opportunity for poleward expansion at the cold edge of its range. Hence, it is possible that the observed changes in butterfly ranges over the past century of concomitant warming and rising atmospheric CO2 concentration are related to matching changes in the ranges of the plants upon which they feed. Or, this similarity could be due to some more complex phenomenon, possibly even some direct physiological effect of temperature and atmospheric CO2 concentration on the butterflies themselves.

In any event, and in the face of the 0.8C of "dreaded" global warming that occurred in Europe over the 20th century, the consequences for European butterflies were primarily beneficial, because, as Parmesan et al. describe the situation, "most species effectively expanded the size of their range when shifting northwards," since "nearly all northward shifts involved extensions at the northern boundary with the southern boundary remaining stable."

Across the Atlantic in America, Fleishman et al. (2001) used comprehensive data on butterfly distributions from six mountain ranges in the U.S. Great Basin to study how butterfly assemblages of that region may respond to IPCC-projected climate change. Whereas prior more simplistic analyses of the type used by climate alarmists to gain support for their anti-CO2 campaigns have routinely predicted the extirpation of great percentages of the butterfly species in this region in response to model-predicted increases in air temperature presumed to be driven by past and projected increases in atmospheric greenhouse gas concentrations, Fleishman et al.'s study revealed that "few if any species of montane butterflies are likely to be extirpated from the entire Great Basin (i.e., lost from the region as a whole)."

In further discussing their results, the three researchers note that "during the Middle Holocene, approximately 8000-5000 years ago, temperatures in the Great Basin were several degrees warmer than today." Thus, they go on say that "we might expect that most of the montane species -- including butterflies -- that currently inhabit the Great Basin would be able to tolerate the magnitude of climatic warming forecast over the next several centuries." Consequently, it would appear that even if the global warming projections of the IPCC were true -- and we sincerely believe they are not -- the many predictions of biological extinctions associated with those projections are almost certainly false.

Returning to the British Isles, Thomas et al. (2001) documented an unusually rapid expansion of the ranges of two butterfly species (the silver-spotted skipper butterfly and the brown argus butterfly) along with two cricket species (the long-winged cone-head and Roesel's bush cricket). In fact, they write that the warming-induced "increased habitat breadth and dispersal tendencies have resulted in about 3- to 15-fold increases in expansion rates."

In commenting on these findings, Pimm (2001) truly states the obvious when he says that the geographical ranges of these insects are "expanding faster than expected," and that the synergies involved in the many intricacies of the range expansion processes are also "unexpected." But does he suggest that these population-enhancing and species-richness-increasing phenomena might possibly bode well for earth's biosphere? Of course not, for that would be politically incorrect. Rather, he pessimistically writes in the lead-in to his commentary that "other species may not be quite so lucky," and he concludes his treatise equally pessimistically by stating that "the broad lesson from Thomas and colleagues' results should not be awe at how quickly a few species benefit from global change, but concern with how rapidly many may be harmed by it."

Isn't it amazing how good news -- even news so good that we stand in "awe" of it -- brings forth even further predictions of disaster from those enamored of the CO2-induced global warming hypothesis? And isn't it amazing that the benefits of the regional warming are said to be restricted to but "a few species," when similar warming-induced range expansions have been documented by Parmesan et al. (1999) for literally dozens of European butterfly species? ... and by Thomas and Lennon (1999) for several species of British birds? Then again, maybe it's not surprising, when science becomes politicized!

But we digress ... and there's still lots more to discuss, such as the work of Crozier (2004), who writes that "Atalopedes campestris, the sachem skipper butterfly, expanded its range from northern California into western Oregon in 1967, and into southwestern Washington in 1990," where she reports that temperatures rose by 2-4C over the prior half-century. Thus intrigued, and in an attempt to assess the importance of this regional warming for the persistence of A. campestris in the recently colonized areas, Crozier "compared population dynamics at two locations (the butterfly's current range edge and just inside the range) that differ by 2-3C." Then, to determine the role of over-winter larval survivorship, she "transplanted larvae over winter to both sites."

This work revealed, in her words, that "combined results from population and larval transplant analyses indicate that winter temperatures directly affect the persistence of A. campestris at its northern range edge, and that winter warming was a prerequisite for this butterfly's range expansion." Noting that "populations are more likely to go extinct in colder climates," Crozier says "the good news about rapid climate change [of the warming type] is that new areas may be available for the introduction of endangered species." Her work also demonstrates that the species she studied has responded to regional warming by extending its northern range boundary and thereby expanding its range, which should enable it to move further back from the "brink of extinction" that so many climate alarmists typically associate with rapid global warming.

Two years later, Davies et al. (2006) introduced their study of the silver-spotted skipper butterfly (Hesperia comma L.) by noting that during the 20th century it "became increasingly rare in Britain [as] a result of the widespread reduction of sparse, short-turfed calcareous grassland containing the species' sole larval host plant, sheep's fescue grass [Festuca ovina L]." As a result, they describe the "refuge" colonies of 1982 as but a "remnant" of what once had been. But the end was not yet; for then came the infamous warming that is said by climate alarmists to have been unprecedented over the past two millennia. Was it to be the final insult that would ultimately drive the decimated species to extinction?

The four researchers analyzed population density data together with estimates of the percentage bare ground and the percentage sheep's fescue available to the butterflies, based on surveys conducted in Surrey in the chalk hills of the North Downs, south of London, in 1982 (Thomas et al., 1986), 1991 (Thomas and Jones, 1993), 2000 (Thomas et al., 2001; Davies et al., 2005) and 2001 (R.J. Wilson, unpublished data). In addition, they assessed egg-laying rates in different microhabitats, as well as the effects of ambient and oviposition site temperatures on egg laying, and the effects of sward composition on egg location. This work revealed, in their words, that "in 1982, 45 habitat patches were occupied by H. comma [but] in the subsequent 18-year period, the species expanded and, by 2000, a further 29 patches were colonized within the habitat network." In addition, they found that "the mean egg-laying rate of H. comma females increased with rising ambient temperatures," and that "a wider range of conditions have become available for egg-laying."

In discussing their findings, Davies et al. state that "climate warming has been an important driving force in the recovery of H. comma in Britain [as] the rise in ambient temperature experienced by the butterfly will have aided the metapopulation re-expansion in a number of ways." First, they suggest that "greater temperatures should increase the potential fecundity of H. comma females," and that "if this results in larger populations, for which there is some evidence (e.g. 32 of the 45 habitat patches occupied in the Surrey network experienced site-level increases in population density between 1982 and 2000), they will be less prone to extinction [our italics]," with "larger numbers of dispersing migrant individuals being available to colonize unoccupied habitat patches and establish new populations." Second, they state that "the wider range of thermal and physical microhabitats used for egg-laying increased the potential resource density within each grassland habitat fragment," and that "this may increase local population sizes." Third, they argue that "colonization rates are likely to be greater as a result of the broadening of the species realized niche, [because] as a larger proportion of the calcareous grassland within the species' distribution becomes thermally suitable, the relative size and connectivity of habitat patches within the landscape increases." Fourth, they note that "higher temperatures may directly increase flight (dispersal) capacity, and the greater fecundity of immigrants may improve the likelihood of successful population establishment." Consequently, Davies et al. conclude that "the warmer summers predicted as a consequence of climate warming are likely to be beneficial to H. comma within Britain," and they suggest that "warmer winter temperatures could also allow survival in a wider range of microhabitats."

In a concurrent study, Menendez et al. (2006) provided what they call "the first assessment, at a geographical scale, of how species richness has changed in response to climate change," concentrating on British butterflies. This they did by testing "whether average species richness of resident British butterfly species has increased in recent decades, whether these changes are as great as would be expected given the amount of warming that has taken place, and whether the composition of butterfly communities is changing towards a dominance by generalist species." By these means they determined that "average species richness of the British butterfly fauna at 20 x 20 km grid resolution has increased since 1970-82, during a period when climate warming would lead us to expect increases." They also found, as expected, that "southerly habitat generalists increased more than specialists," which require a specific type of habitat that is sometimes difficult for them to find, especially in the modern world where habitat destruction is commonplace. In addition, they were able to determine that observed species richness increases lagged behind those expected on the basis of climate change.

These results "confirm," according to the nine UK researchers, "that the average species richness of British butterflies has increased since 1970-82." However, some of the range shifts responsible for the increase in species richness take more time to occur than those of other species; and they say their results imply that "it may be decades or centuries before the species richness and composition of biological communities adjusts to the current climate."

Also working in Britain, Hughes et al. (2007) examined evolutionary changes in adult flight morphology in six populations of the speckled wood butterfly -- Pararge aegeria L. (Satyrinae) -- along a transect from its distribution core to its warming-induced northward expanding range margin. The results of this exercise were then compared with the output of an individual-based spatially explicit model that was developed "to investigate impacts of habitat availability on the evolution of dispersal in expanding populations." This work indicated that the empirical data the researchers gathered "were in agreement with model output," and that they "showed increased dispersal ability with increasing distance from the distribution core," which included favorable changes in thorax shape, abdomen mass and wing aspect ratio for both males and females, as well as thorax mass and wing loading for females. In addition, they say that "increased dispersal ability was evident in populations from areas colonized >30 years previously."

In discussing their findings, Hughes et al. suggest that "evolutionary increases in dispersal ability in expanding populations may help species track future climate changes and counteract impacts of habitat fragmentation by promoting colonization." However, they report that in the specific situation they investigated, "at the highest levels of habitat loss, increased dispersal was less evident during expansion and reduced dispersal was observed at equilibrium, indicating that for many species, continued habitat fragmentation is likely to outweigh any benefits from dispersal." Put another way, it would appear that global warming is proving not to be an insurmountable problem for the speckled wood butterfly, which is evolving physical characteristics that allow it to better keep up with the poleward migration of its current environmental niche, but that the direct destructive assaults of humanity upon its natural habitat could still end up driving it to extinction.

Analyzing data pertaining to the general abundance of Lepidoptera in Britain over the period 1864-1952, based on information assembled by Beirne (1955) via his examination of "several thousand papers in entomological journals describing annual abundances of moths and butterflies," were Dennis and Sparks (2007), who report that "abundances of British Lepidoptera were significantly positively correlated with Central England temperatures in the current year for each month from May to September and November," and that "increased overall abundance in Lepidoptera coincided significantly with increased numbers of migrants," which latter data were derived from the work of Williams (1965). In addition, they report that Pollard (1988) subsequently found much the same thing for 31 butterfly species over the period 1976-1986, and that Roy et al. (2001) extended the latter investigation to 1997, finding "strong associations between weather and population fluctuations and trends in 28 of 31 species which confirmed Pollard's (1988) findings," all of which observations indicate that the warming-driven increase in Lepidopteran species and numbers in Britain has been an ongoing phenomenon ever since the end of the Little Ice Age.

Returning to North America for one final study, White and Kerr (2006), as they describe it, "report butterfly species' range shifts across Canada between 1900 and 1990 and develop spatially explicit tests of the degree to which observed shifts result from climate or human population density," the latter of which factors they describe as "a reasonable proxy for land use change," within which broad category they include such things as "habitat loss, pesticide use, and habitat fragmentation," all of which anthropogenic-driven factors have been tied to declines of various butterfly species. In addition, they say that to their knowledge, "this is the broadest scale, longest term dataset yet assembled to quantify global change impacts on patterns of species richness."

This exercise led White and Kerr to discover that butterfly species richness "generally increased over the study period, a result of range expansion among the study species," and they further found that this increase "from the early to late part of the 20th century was positively correlated with temperature change," which had to have been the cause of the change, for they also found that species richness was "negatively correlated with human population density change." Contrary to the doom-and-gloom prognostications of the world's climate alarmists, therefore, the supposedly unprecedented -- and dreaded -- global warming of the 20th century has been nothing but beneficial for the butterfly species that inhabit Canada, as their ranges have expanded and greater numbers of species are now being encountered in most areas of the country.

And so it has been essentially everywhere similar studies have been conducted: rising air temperatures and atmospheric CO2 concentrations are promoting range expansions of the world's butterfly species, leading to increased local biodiversity wherever butterflies are to be found.

Beirne, B.P. 1955. Natural fluctuations in abundance of British Lepidoptera. Entomologist's Gazette 6: 21-52.

Crozier, L. 2004. Warmer winters drive butterfly range expansion by increasing survivorship. Ecology 85: 231-241.

Davies, Z.G., Wilson, R.J., Brereton, T.M. and Thomas, C.D. 2005. The re-expansion and improving status of the silver-spotted skipper butterfly (Hesperia comma) in Britain: a metapopulation success story. Biological Conservation 124: 189-198.

Davies, Z.G., Wilson, R.J., Coles, S. and Thomas, C.D. 2006. Changing habitat associations of a thermally constrained species, the silver-spotted skipper butterfly, in response to climate warming. Journal of Animal Ecology 75: 247-256.

Dennis, R.L.H. and Sparks, T.H. 2007. Climate signals are reflected in an 89 year series of British Lepidoptera records. European Journal of Entomology 104: 763-767.

Fleishman, E., Austin, G.T. and Murphy, D.D. 2001. Biogeography of Great Basin butterflies: revisiting patterns, paradigms, and climate change scenarios. Biological Journal of the Linnean Society 74: 501-515.

Goverde, M., Bazin, A., Shykoff, J.A. and Erhardt, A. 1999. Influence of leaf chemistry of Lotus corniculatus (Fabaceae) on larval development of Polyommatus icarus (Lepidoptera, Lycaenidae): effects of elevated CO2 and plant genotype. Functional Ecology 13: 801-810.

Goverde, M., Erhardt, A. and Niklaus, P.A. 2002. In situ development of a satyrid butterfly on calcareous grassland exposed to elevated carbon dioxide. Ecology 83: 1399-1411.

Goverde, M., Erhardt, A. and Stocklin, J. 2004. Genotype-specific response of a lycaenid herbivore to elevated carbon dioxide and phosphorus availability in calcareous grassland. Oecologia 139: 383-391.

Hughes, C.L., Dytham, C. and Hill, J.K. 2007. Modelling and analyzing evolution of dispersal in populations at expanding range boundaries. Ecological Entomology 32: 437-445.

Leadley, P.W., Niklaus, P., Stocker, R. and Korner, C. 1997. Screen-aided CO2 control (SACC): a middle-ground between FACE and open-top chamber. Acta Oecologia 18: 207-219.

Leadley, P.W., Niklaus, P.A., Stocker, R. and Korner, C. 1999. A field study of the effects of elevated CO2 on plant biomass and community structure in a calcareous grassland. Oecologia 118: 39-49.

Menendez, R., Gonzalez-Megias, A., Hill, J.K., Braschler, B., Willis, S.G., Collingham, Y., Fox, R., Roy, D.B. and Thomas, C.D. 2006. Species richness changes lag behind climate change. Proceedings of the Royal Society B 273: 1465-1470.

Parmesan, C., Ryrholm, N., Stefanescu, C., Hill, J.K., Thomas, C.D., Descimon, H., Huntley, B., Kaila, L., Kullberg, J., Tammaru, T., Tennent, W.J., Thomas, J.A. and Warren, M. 1999. Poleward shifts in geographical ranges of butterfly species associated with regional warming. Nature 399: 579-583.

Pimm, S.L. 2001. Entrepreneurial insects. Nature 411: 531-532.

Pollard, E. 1988. Temperature, rainfall and butterfly numbers. Journal of Applied Ecology 25: 819-828.

Roy, D.B., Rothery, P., Moss, D., Pollard, E. and Thomas, J.A. 2001. Butterfly numbers and weather: predicting historical trends in abundance and the future effects of climate change. Journal of Animal Ecology 70: 201-217.

Thomas, C.D., Bodsworth, E.J., Wilson, R.J., Simmons, A.D., Davies, Z.G., Musche, M. and Conradt, L. 2001. Ecological and evolutionary processes at expanding range margins. Nature 411: 577-581.

Thomas, C.D. and Jones, T.M. 1993. Partial recovery of a skipper butterfly (Hesperia comma) from population refuges: lessons for conservation in a fragmented landscape. Journal of Animal Ecology 62: 472-481.

Thomas, C.D. and Lennon, J.J. 1999. Birds extend their ranges northwards. Nature 399: 213.

Thomas, J.A., Thomas, C.D., Simcox, D.J. and Clarke, R.T. 1986. Ecology and declining status of the silver-spotted skipper butterfly (Hesperia comma) in Britain. Journal of Applied Ecology 23: 365-380.

White, P. and Kerr, J.T. 2006. Contrasting spatial and temporal global change impacts on butterfly species richness during the 20th century. Ecography 29: 908-918.

Williams, C.B. 1965. Insect Migration. Collins, London, UK, 237 pp.

Last updated 31 December 2008