Climatic change and insect distributions

The modeling techniques above lend themselves to back-tracking, allowing reconstruction of past species distributions based on models of previous climate and/or reconstruction of past climates based on postglacial fossil remains representing past distributional information. Such studies were based originally on pollen remains (palynology) from lake benthic cores, in which rather broad groups of pollens, with occasional indicative species, were used to track vegetational changes through time, across landscapes, and even associated with previous climates. More refined data came from preserved ostracods, beetles (especially their elytra), and the head capsules of larval chironomids. These remnants of previous inhabitants derive from short-lived organisms that appear to respond rapidly to climatic events. Extrapolation from inferred bio-climatic controls governing the present-day distributional range of insect species and their assemblages to those same taxa preserved at time of deposition allows

Fig. 6.16 Modeled distribution for Austrochlus species (Diptera: Chironomidae) based on presence data. Black, predicted presence within 98% confidence limits; pale gray, within 95% confidence. (After Cranston et al. 2002.)

reconstructions of previous climates. For example, major features from the late Quaternary period include a rapid recovery from extreme conditions at the peak of last glaciation (14,500 years ago), with intermittent reversal to colder periods in a general warming trend. Verification for such insect-based reconstructions has come from independent chemical signals and congruence with a Younger Dryas cold period (11,40010,500 years ago), and documented records in human history such as a medieval 12th century warm event and the 17th century Little Ice Age when "ice fairs" were held on the frozen River Thames. Inferred changes in temperatures range from 1 to 6°C, sometimes over just a few decades.

Confirmation of past temperature-associated biotic changes leads to the advocacy of such models to predict future range changes. For example, estimates for disease-transmitting mosquitoes and biting midges under different climate-change scenarios have ranged from naive estimates of increased range of disease vectors into populated areas currently disease-free (where vectors actually already exist in the absence of the virus) to sophisticated models accounting for altered development rates for vector and arbovirus, and altered environments for larval development. Future levels of predicted climate change remain unclear, allowing certain policy-makers to deny its existence or its biotic significance. However, by the turn of the millennium Europe had warmed 0.8°C in the 20th century and realistic expectations are for a further increase of between 2.1 and 4.6°C mean global change in this century, along with commensurate variation in other climatic factors such as seasonality and rainfall. That predicted changes in distributions of insects are occurring is evident from studies of individual species of butterflies and odonates. A study of species of western European butterflies (limited to non-migrants and excluding monophagous and/or geographically restricted taxa) is quite conclusive. Northward extension of ranges has been shown for many taxa (63% of 57 species), whereas only two species have shifted south. For the many butterfly species for which boundaries have moved, an observed range shift of from 35 to 240 km in the past 30 -100 years coincided quite closely with the (north-) polewards movement of the isotherms over the period. That such range changes have been induced by a modest temperature increase of less than 1°C surely is a warning of the dramatic effects of the ongoing "global warming" over the next century.

One order of insects at particular risk from climate change is the Grylloblattodea. All of the North American species (genus Grylloblatta) are dependent on snow fields, ice caves, and glacier habitats and these are under threat from global warming. For example, the rate of glacier melt is predicted to increase 2 -4-fold compared with the current, already high rate of loss. Recent searches have failed to find several Californian Grylloblatta species, apparently due to climate-induced loss of their habitats.

Climate change can lead to early emergences of insect species or populations in the spring and summer. For example, long-term records from the Central Valley of California show that the first flight date of 70% of

23 butterfly species was advanced by an average of

24 days over a period of 31 years, with climate factors explaining most of the variation in this trend. An associated phenomenon is the increasing phenological asynchrony seen in some insect/plant systems, with insect activity becoming mismatched with availability of their host plants. Similar changes in the activity periods of host insects and their parasitoids may lead to higher or lower levels of parasitization, depending on individual temperature responses of the interacting species. Such trophic asynchronies may have serious ecological consequences and lead to species declines or extinctions.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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