Responses of insects to the current climate changes: from physiology and behavior to range shifts
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- Musolin, D.L. & Saulich, A.K. Entmol. Rev. (2012) 92: 715. doi:10.1134/S0013873812070019
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Climate change (first of all the rise in temperature) is currently considered one of the most serious global challenges facing mankind. Here we review the diversity of insect responses to the current climate warming, with particular focus on true bugs (Heteroptera). Insects as ectotherms are bound to respond to the temperature change, and different species respond differently depending on their specific physiological and ecological traits, seasonal cycle, trophic relations, etc. Insect responses to climate warming can be divided into six categories: changes in (1) ranges, (2) abundance, (3) phenology, (4) voltinism, (5) morphology, physiology, and behavior, and (6) relationships with other species and in the structure of communities. Changes in ranges and phenology are easier to notice and record than other responses. Range shifts have been reported more often in Lepidoptera and Odonata than in other insect orders. We briefly outline the history and eco-physiological background of the recent range limit changes in the Southern green stink bug Nezara viridula (Heteroptera, Pentatomidae) in central Japan. Range expansion in individual species can lead to enrichment of local faunas, especially at high latitudes. Phenological changes include not only advances in development in spring but also shifts in phenology later in the season. The phenophases related to the end of activity usually shift to later dates, thus prolonging the period of active development. This may have both positive and negative consequences for the species and populations. As with any other response, the tendencies in phenological changes may vary among species and climatic zones. The proven cases of change in voltinism are rare, but such examples do exist. Application of models based on thermal parameters of development suggests that a rise in temperature by 2°C will result in an increased number of annual generations in many species from different arthropod taxa (up to three or four additional generations in Thysanoptera, Aphidoidea, and Acarina). The warming-mediated changes in physiology, morphology, or behavior are difficult to detect and prove, first of all because of the absence of reliable comparative data. Nevertheless, there are examples of changes in photoperiodic responses of diapause induction and behavioral responses related to search of shelters for summer diapause (aestivation). Since (1) individual species do not exist in isolation and (2) the direction and magnitude of responses even to the same environmental changes vary between species, it may be expected that in many cases the current stable relationships between species will be affected. Thus, unequal range shifts in insects and their host plants may disrupt their trophic interactions near the species’ range boundaries. Studies of responses to climate warming in more than one interrelated species or in entire communities are extremely rare. The loss of synchronism in seasonal development of community members may indicate inability of the higher trophic levels to adapt fully to climate warming or an attempt of the lower trophic level to escape from the pressure of the higher trophic levels. It is generally supposed that many insect species in the Temperate Climate Zone will benefit in some way from the current climate warming. However, there is some experimental evidence of an opposite or at least much more complex response; the influence of warming might be deleterious for some species or populations. It is suggested that species or populations from the cold or temperate climate have sufficient phenotypic plasticity to survive under the conditions of climate warming, whereas species and populations which already suffer from stress under extreme seasonal temperatures in warmer regions may have a limited “maneuver space” since the current temperatures are close to their upper thermal limits. Without genetic changes, even moderate warming will put these species or populations under serious physiological stress. The accumulated data suggest that responses of insects and the entire biota to climate warming will be complex and will vary depending on the rate of warming and ecological peculiarities of species and regions. Physiological responses will vary in their nature, direction, and magnitude even within one species or population, and especially between seasons. The responses will also differ in different seasons. For example, warming may negatively affect nymphal development during the hot season but at the same time accelerate growth and development during the cold season and/or ensure milder and more favorable overwintering conditions for adults. All these factors will affect population dynamics of particular species and relationships among the members of ecosystems. We should keep in mind that (1) not only selected insect species but almost all the species will be affected, (2) temperature is not the only component of the climatic system that is changing, and (3) responses will be different in different seasons. Host plants, phytophagous insects, their competitors, symbionts, predators, parasites, and pathogens will not only respond separately to climate changes; individual responses will further affect the responses of other species, thus making reliable prediction extremely complicated. Responses are expected to (1) be species- or population-specific, (2) concern basically all the aspects of organism/ species biology and ecology (individual physiology, population structure, abundance, local adaptations, phenology, voltinism, and distribution), and (3) occur at scales ranging from an undetectable cellular level to major distribution range shifts or regional extinctions. The scale of insect responses will depend on the extent and rate of climate warming. Slight to moderate warming may cause responses only in a limited number of species with more flexible life cycles, whereas a substantial increase in temperature may affect a greater number of different species and ecological groups.