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- Kolb, Gundula S., 1978-, et al.
(författare)
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Ecological stoichiometry and homeostasis of plants and invertebrates on and nearby heavily fertilized cormorant nesting islands
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Ecological stoichiometry has generalized the fundamental role of individual nutrient demand in all ecological processes and interactions. It implies that the elemental composition (C:N:P) of a consumer relative to the C:N:P of its resource determines its growth rate and thus secondary productivity. A central, but recently questioned, principle of ecological stoichiometry is the assumption that heterotrophs, in contrast to autotrophs, keep their elemental composition strongly homeostatic. Since neither the relationship between consumer C:N:P and its numeric response to changes in resource C:N:P nor the C:N:P homeostasis of arthropods have been extensively studied for arthropods, we used a natural gradient of N and P loads, in form of seabird and non-seabird islands, to investigate the stoichiometry and homeostasis of primary producers and invertebrates, both on and around islands. We then looked for causal relationships between stoichiometry and the level of homeostasis of a taxonomic group, respectively, and observed numerical responses to seabird fertilization. We found in accordance to principal theories that invertebrates, generally, strongly regulated their stoichiometry while autotrophs were stoichiometrically plastic. Thus, we found no causal relationship between consumer homeostasis and displayed numeric responses. Furthermore, we found only weak support for the hypothesis that the C:N:P of a taxa determines its numeric response to increased resource nutrient content (lepidopteran larvae had high P:C and high abundance on P-rich cormorant islands). We conclude that other species traits than nutrient content mainly determine the success of a taxa in a certain environment. Additionally, due to the strong effects of different level of homeostasis on ecological interactions, food web dynamics and nutrient cycles, we underline the need of further studies on the homeostasis of arthropods.
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- Kolb, Gundula S., 1978-
(författare)
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The impact of cormorant nesting colonies on plants and arthropods
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Seabirds concentrate large amounts of marine nutrients on their nesting islands. This nutrient input can have large consequences for island food webs and community structure. The high nutrient load may also cause runoff into surrounding waters and affect marine communities. In my thesis, I studied the effect of cormorant nesting colonies on the stoichiometry, abundance, species richness, and species composition of plants, algae, and invertebrates on land and in costal waters and investigated if differences in the elemental composition or homeostasis can explain differences in the numerical response among invertebrate groups. δ15N analysis indicated that ornithogenic nitrogen provided a significant nitrogen source for plants and arthropods on nesting islands and around high nest density islands also for brackish algae and invertebrates. Furthermore, nutrient runoff created a potential feed-back loop to spiders via chironomids. Cormorant nutrient input changed island vegetation and increased plant P and N content and epiphytic algae:Fucus ratio, but decreased plant species richness and vegetation cover. Invertebrates responded indirectly to these qualitative and quantitative changes in their food source and habitat, but also directly to cormorant subsidies. However not all taxonomic and feeding groups were affected and responses were both positive and negative. Differences in the numerical response among taxonomic groups could not be explained by differences in the level of homeostasis, since, generally, all invertebrates were strongly homeostatic. Similarly, consumer nutrient content was a poor predictor for displayed responses. I conclude that cormorant colonies have strong impacts on island vegetation and some consumer groups. However, even if they can decrease the species richness of some organism groups on their nesting islands, they increase the habitat heterogeneity in an archipelago and thus may increase the regional species diversity.
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