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- Andersson, Petter
(författare)
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Olfactory cues and insects - scaling relations and immigration rates
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For herbivorous insects, location of host plants and habitat patches strongly depend on the type of sensory cue that is used during the search process and the probability of detecting a patch depends on the relative attraction between patches of different size. The visual impression of a patch increases predictably with the patch diameter and consequently, immigration rates of visually searching insects are often predicted by the scaling to patch size of visual cues. However, for olfactory cues, the relative attraction between small and large patches is unknown, but has been suggested to increase faster with patch size than visual information. In this thesis, I explore the scaling relation between olfactory cues and patch size. I measured odor attraction of patches of different size and estimated scaling rules for olfactory information. The estimated scaling rules were tested with simulations and a field experiment, where immigration rates of olfactory searching insects were quantified. The estimated scaling rules for olfactory information suggested that the relative attraction did not deviate fundamentally from the scaling of visual cues to patch size. Both the simulations and the field immigration experiment supported this suggestion. Therefore, I conclude that visual and olfactory cues scale roughly to patch size in a similar way, i.e. to the patch diameter. This thesis demonstrates the importance of considering species traits for the understanding of insect responses to habitat heterogeneity.
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| 2. |
- Andersson, Petter
(författare)
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Quantitative aspects of plant-insect interactions in fragmented landscapes : the role of insect search behavior
- 2009
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- Insects searching for host plants in the landscape are challenged by habitat fragmentation and heterogeneity. Host plants or habitat are usually distributed in scattered patches that may differ in size, shape and isolation. The ability of finding these patches strongly depends on the insect´s search behavior and the sensory cues used for detecting and locating patches. Here, I describe sensory systems of insects, such as vision, olfaction and taste, in relation to host plant search. I discuss quantitative patterns of insect distributions and density-area relations arising from search behavior. Migration pattern may be strongly affected by the cue used by the insect in the patch detection process. The relation between visual cues and patch size is well known, but we lack knowledge about how olfactory cues are connected to patch size. Since search behavior affects the spatial distribution of insects, I briefly describe consequences for host plants. Finally, I describe the main objectives of my PhD-project.
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| 4. |
- Dahlberg, Johan, 1978-
(författare)
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Range margins and refugia
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Species ranges are restricted in distribution by physical barriers, dispersal ability, abiotic factors such as climate and interspecific interactions. The responses of a species to environmental conditions and biotic factors determine its abundance, distribution and range limits. There are four possible responses for populations facing global climate change. They can acclimate, adapt, shift their ranges or go extinct. During unfavorable conditions populations may shift their ranges and survive in refugia with favorable environmental features. Thereafter they might be able to return to their former distribution when the conditions get favorable again. The term refugium has been used for large scale refugia such as interglacial and glacial refugia (macrorefugia), and for small scale refugia such as microrefugia. The existence of microrefugia is promoted by decoupling of the local climate from the regional climate because this buffers against climate change. Such decoupling is most likely to occur in heterogeneous landscapes. At a range shift, new microrefugia may arise at the eroding edge, while macrorefugia may form from a contracting main (continuous) range.
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| 5. |
- Fors, Lisa, 1976-
(författare)
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Interactions and Coevolution in Tritrophic systems
- 2012
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Ecological systems are usually complex, with a number of interacting species. These species interactions are commonly divided into two major groups: mutualistic and antagonistic. If the interactions are mutualistic, they are beneficial for all species involved, as in specialized relationships between certain plants and their pollinators. Antagonistic interactions, on the other hand, can be either competitive or trophic. Trophically interacting species are for example plants and their associated herbivores, predators and their prey or parasites and their hosts. In many of these interactions, some species are depending on others in order to survive. If one species changes, other species associated to it may have to adapt to the changes. This may lead to a process of reciprocal evolution between the interacting species, called coevolution. In this paper I start with a brief background on coevolution and local adaptation, and then describe some interactions in tritrophic systems. The tritrophic systems I focus on consist of plants, herbivore insects and parasitoids. I discuss some processes and mechanisms in these systems, such as host search, plant defense and the immune response in insects. In the end of the paper, a short description of my PhD-project is included.
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| 6. |
- Forslund, Helena, 1978-
(författare)
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Grazing and the geographical range of seaweeds : The introduced Fucus evanescens and the newly described Fucus radicans
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Along the coast of temperate oceans brown algae of the genus Fucus form dense stands on rocky shores and are keystone species of the coastal ecosystem. These large seaweeds are perennial and function as substrate for many sessile marine organisms, provide shelter for fauna and juvenile fish, and are food source. A number of abiotic (e.g. wave-exposure, salinity and substrate) and biotic (e.g. herbivory and competition) factors structures these communities and determines the abundance and composition of fucoids at each specific site. Earlier studies have shown that herbivores may reduce growth of fucoids, thus affecting their distribution, and at high densities eliminate the species from previously occupied sites. In my thesis I focused on investigating herbivore-seaweed interactions and whether such interactions could influence the geographical range limits of Fucus species. A set of laboratory bioassays and a field survey were conducted (1) to investigate the resistance to grazing by a generalist gastropod between introduced (to Sweden) and native (Iceland) Fucus evanescens (Paper I), (2) to study the distribution pattern of F. radicans and F. vesiculosus along the Swedish coast and specifically the southern limit of F. radicans, (3) to examine the abundance of herbivores in these two species, and (4) to test the hypothesis that Idotea baltica may contribute to restrict F. radicans to the Bothnian Sea (objective 2-4; Paper II). Fucus evanescens, a species that was introduced to the Swedish coast about 100 years ago, was found to be more resistant to grazing by L. littorea compared to F. evanescens from the native Icelandic populations. It was also shown to contain a higher amount of phlorotannins; a putative chemical defence to herbivory. This indicates that development of resistance to herbivory could be important for a successful introduction and survival in a new range. No gradual change in the proportion, measured as % cover of either F. radicans or F. vesiculosus was found inside the range of F. radicans and its southernmost limit was abrupt without any corresponding abrupt change in any abiotic factor, e.g. salinity. Herbivores, i.e. Idotea spp., Gammarus spp. and Theodoxus fluviatils were found to be more abundant in F. radicans than in F. vesiculosus thalli indicating a habitat preference for F. radicans. Further, Idotea baltica, whose range only overlaps with that of F. radicans in the south, was shown to prefer F. radicans over F. vesiculosus, possibly due to its lower content of phlorotannins. Based on these findings I propose that Idotea species may contribute in restricting the southern range of F. radicans, although further experiments, especially regarding competition with the larger F. vesiculosus need to be performed. In conclusion, biotic interactions e.g. the ability of to resist herbivore grazing by e.g. high phlorotannin content or having a structure less attractive as habitat to herbivores may be of importance in determining the geographic range of fucoids.
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