Chironomids (Diptera, Nematocera) of Temporary Pools - an Ecological Case Study
The main aim of the present study was to determine how Chironomidae cope with the environmental changes to which temporary pools are exposed. Are the species specifically adapted to the habitat or opportunistic? The problem was approached by: (a) an emergence study done in the Lahnbe...
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| Format: | Doctoral Thesis |
| Language: | English |
| Published: |
Philipps-Universität Marburg
2003
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| Online Access: | PDF Full Text |
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| Summary: | The main aim of the present study was to determine
how Chironomidae cope with the environmental changes to which
temporary pools are exposed. Are the species specifically
adapted to the habitat or opportunistic? The problem was
approached by: (a) an emergence study done in the Lahnberge
mountain range (Marburg, Hesse, Germany) on three pools that
were subjected to different lengths of drought (two of which
were really temporary and one semi permanent); (b) an emergence
study done in order to investigate the dispersal ability of
Chironomus dorsalis (colonizing experiment) in ten experimental
pools that had been exposed in the field in 1998 and that
mimicked spatially unstable pools; (c) laboratory
investigations of some fundamental biological characteristics
(role of temperature, photoperiod and density in growth and
development, drought tolerance and parthenogenesis) of the four
principal temporary pool dwellers Limnophyes asquamatus,
Paralimnophyes hydrophilus, C. dorsalis and Polypedilum tritum.
Contrasting with what is known for many other inhabitants of
temporary pools (e.g. mosquitoes or water beetles), the
temporary pool chironomids presently investigated showed only
one programmed life history trait - the way of the annual
timing - which is widespread amongst Chironomidae. All other
life history traits were highly flexible and consecutively
followed the actual situation within the habitat. The life
histories of Limnophyes asquamatus, Paralimnophyes hydrophilus,
Chironomus dorsalis and Polypedilum tritum are therefore rather
opportunistic. A mixture of r- and A-selected traits achieves
this enormous flexibility, which also seems to be widespread
amongst Chironomidae. The ability to enter dormancy when
environmental factors go below/beyond a given limit is the
central element of the species? life histories. I call
this capacity the quiescence strategy of Chironomidae, the
knowledge of which is still fragmentary. Facultative dormancy,
high levels of physiological tolerance of the larvae and many
r-selected traits, lead to a high plasticity of life histories.
The fine-tuning to the temporary habitat has been mainly
achieved by an adaptive improvement of a few preadaptive
properties present in Chironomidae: (a) The effective
colonization of spatially unstable temporary pools was mainly
achieved by the improvement of the dispersal abilities in
Chironomus dorsalis; (b) The improvement of larval drought
tolerance and its related features (such as acceleration of
development at high larval densities and the capacity for
terrestrial eclosion) enabled Limnophyes asquamatus,
Paralimnophyes hydrophilus and Polypedilum tritum to
effectively colonize spatially stable temporary pools. The
evolution of an expert invader as well as of drought tolerance
can be regarded as a strategy of being the first: the first
species present after pool formation has the decisive
advantages of (a) larger larval size in relation to other
potential competitors and; (b) low numbers of predators. Many
other insects of temporary waters were forced to evolve life
cycles specifically linked to drought because they are able to
survive drought only in a species-specific development stage
(e.g. the egg stage in mosquitoes). This was quite different in
the drought tolerant species investigated in the present study:
all instars proved to be drought tolerant and resumed
development without any risk whenever water was present.
Whether the high thermal coefficients (4-6) over a wide range
of favourable temperatures (5-15 °C) for growth and development
that were observed in Paralimnophyes hydrophilus are really an
adaptive feature still remains questionable. |
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| DOI: | 10.17192/z2004.0076 |