Natural Shift and Strategies of Insects in Rising Temperatures

The effects of global warming on the phenology and distribution of plants and animals were recently well summarized and analyzed by Parmesan (2006). The available studies have demonstrated that climate change has had a strong impact on marine, freshwater, and terrestrial groups in various regions of the world (North and South Poles, temperate and tropical regions, and oceans) and with wide-ranging consequences (i.e., shifts in the distribution of species, range contraction, extinction, community reorganization, and alteration of predator-prey and plant-insect interactions).

Polar and mountaintop species have experienced severe range contractions and are the first groups in which entire species have become extinct due to recent changes in climate. In southern France, populations of the cool-adapted Apollo butterfly (Parnassius apollo) have become extinct over the past 40 years in mountainous areas less than 850 m high but have remained healthy in higher regions in the station at elevations greater than 900 m asl. An evident relation between the shift of altitudinal species and the rise in temperatures was documented in Spain, where the lower altitudinal limits of 16 species of butterfly have risen an average of 212 m in 30 years, concurrent with a 1.3°C rise in mean annual temperatures. Plant, bird, and marine life in Antarctica have exhibited profound responses to climate change. The extensive decline in sea-ice extent appears to have stimulated a trophic cascade effect in biological systems. Declines in sea-ice have apparently reduced the abundance of ice algae, which in turn has led to declines in krill, the primary food resource for many fish, seabirds, and marine mammals, with direct consequences in their distribution and population. The extreme effects of global warming on marine communities is well documented at all ecological levels; and climatic variables are in fact responsible for the distribution and dynamics of marine plankton and fish. Phytoplankton and zooplankton communities have experienced strong shifts in tune with regional oceanic climate regime shifts, as well as expected poleward range shifts and changes in the timing of peak biomass. Particularly the sea-ice-dependent Adelie and emperor penguins (Pygoscelis adeliae and Aptenodytes forsteri, respectively), have almost disappeared from their northernmost sites around Antarctica since 1970.

Changes in climate have also had a dramatic impact on the distribution of terrestrial species in temperate regions. Evident shifts in temperate species of the Northern Hemisphere were well documented in Great Britain, where various taxa were examined. In this area, northward shifts of 18.9 km over a 20-year period were observed in 12 bird species (Thomas and Lennon 1999). The same results were also obtained by studying the distribution of various insect groups (Lepidoptera, Odonata, Orthoptera). Several species of butterfly that were mobile and habitat generalists were found to have expanded north or, in smaller portions, had contracted southward (Parmesan 2006). The distribution change closely matched changes in population densities. It was demonstrated that the impact of global climate change also involved the distribution of species living in tropical areas, resulting in movements or outbreaks of tropical species into more-temperate areas. This was observed for the rufous hummingbird, which has undergone an evident shift in its winter range during the last 30 years from Mexico to the southern United States. Tropical insects have also expanded their distribution e.g., Odonata in the southern United States and the black soldier fly (Diptera, Stratyiomidae) all over the word.

It seems that in the environment will soon prevail on grasslands and herbal ecosystems than forestall biomes, with an enlargement of desert in tropical zones. These new conditions favor herbivorous insects not linked to specific plant-host relationships or induce one host plant's insects to feed on several more widespread plants, as demonstrated for some British butterflies (Hill et al. 2002; Thomas et al. 2001). Highly mobile species, whose breeding habitat is widespread, are likely to track climate changes, when sedentary species have few opportunities to shift their ranges. The speed of expanding species is increased by the emergence of dispersive phenotypes exhibiting increased flight ability. This was demonstrated by Thomas and coworkers (2001) for two species of bush crickets from Britain and by Nimela and Spence (1991) in the ground beetle (Carabidae) invading Canada. In both cases these are populations with wing length polymorphism, and in the marginal areas the long-wing specimens were prevalent (Zera and Denno 1997). In other cases, reported by Hill et al. (1999a, b) for butterflies, thorax size and thoracic flight muscles increased because of a changed during of larval stages. Other similar modification of the behavior and the phenotype led us to think that in many cases evolutionary changes could be a more rapid, convenient response to the rapid climate change than migration to nearby habitats.

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