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National Repository of Grey Literature 3 records found  Search took 0.00 seconds. 
Struktura společenstev hálky tvořících členovců na vrbách
 KADLEC, Jan
In this thesis, I examined ecological factors that affect diversity and abundance of galls on willows. I focused on the effects of host-plant phylogeny, host-plant defences, and the effects of interactions among herbivorous guilds. I show that gall abundace is mainly affected by host-plant nutrients, while the defensive traits have only marginal effect. The effect of host-plant phylogeny seems to differ betwen groups of gall-forming arthropod taxa, with several of gall forming species on willows being polyphangous and showing only limited response to willow phylogeny. On the whole, the response of gallers largely differes from the response of less specialized guilds of herbivores.
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Specificity of insect-plant associations and their role in the formation of plant defenses and speciation
 VOLF, Martin
The aim of this dissertation is to investigate what role insect-plant interactions play in the formation of host-plant defenses and in the diversification of both groups. We show that various groups of herbivore respond differently to host-plant defenses. Therefore plant defenses diversify into suites of complementary traits, as individual traits fail to provide protection against specialized herbivores. Further, we identify what levels of host-phylogeny shape the food-web structure of insect herbivores. We show that specialized herbivores are affected mainly by the terminal parts of the host-phylogeny. In contrast, more polyphagous guilds are affected mainly by the mid-levels of the host phylogeny because the effects of terminal or deeper phylogeny seem to be surpassed by other factors in more generalist insect species. In the last chapter, we show how specialized insect-plant interactions generated by tight insect-plant coevolution can influence the speciation in plants over environmental gradients.
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Insect herbivores drive the loss of unique chemical defense in willows
 VOLF, Martin
The thesis examines the effects of chemical and mechanical defensive traits on insects in a local community of 11 Salicaceae species growing in sympatry. The results repeated loss of willow specialized chemical defense. This could be due to its low protective value and high energy costs. Our study thus shows that the balance between costs and benefits of defensive traits is not necessarily in favor of specialized defenses and illustrates a process, which may lead to the reduction in a defensive trait.
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