Ecological drivers of community assembly across taxonomic groups and trophic levels
Başlık çevirisi mevcut değil.
- Tez No: 401072
- Danışmanlar: PROF. ERIK JEPPESEN, PROF. JENS CHRISTIAN SVENNING
- Tez Türü: Doktora
- Konular: Çevre Mühendisliği, Environmental Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2013
- Dil: İngilizce
- Üniversite: Aarhus Universitet
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 204
Özet
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Özet (Çeviri)
This thesis aimed at elucidating ecological factors aff ecting community assembly in two study systems: (i) breeding bird communities sampled at 433 locations across north-west Turkey in 2009 and (ii) plankton communities sampled in c. 400 lakes across Denmark between 1989 and 2009. Community assembly is a complex phenomenon driven by the interplay between environmental species sorting, ecological interactions between species and dispersal, linking local communities with the surrounding communities as well as with their regional populations. Although the research on community assembly is century-old, current understanding is still poor, especially regarding the interaction of these factors across spatial and temporal scales. Five studies have been carried out in this thesis to obtain a better understanding of community assembly in space and time and the role of biotic interactions. Local richness and community composition of forest birds in the Istranca forests were signifi cantly related to forest structure, habitat diversity and altitude, while non-environmental spatial factors also had important, albeit weaker, eff ects, suggesting a secondary role of dispersal and/or biotic interactions. Local bird abundance was strongly linked with occupancy across the metacommunity (the bird communities in the Istranca landscape) as well as the species' regional population and range size across the western Palearctic. Null model analyses showed that bird occupancy was non-randomly related to species environmental niche. Furthermore, species abundance and occupancy across both the metacommunity and the whole western Palearctic were signifi cantly related to an independent species specialization index calculated for the French birds. Together these results indicated that forest bird community assembly is primarily controlled by consistent environmental species sorting across spatial scales and geography locations. Local environmental factors, mainly nutrients, were also the prime determinants of phytoplankton genera richness in 195 Danish lakes. The roles of lake water chemistry, lake morphology, land-use in lake catchments and climate in determining the richness of diff erent phytoplankton groups refl ect the diff erences in their ecology. There was spatial structure at local to landscape scale (< 30 km) in phytoplankton richness after accounting for the local environmental diff erences, probably refl ecting catchment-scale connectivity among lakes mediating the dispersal of organisms as well as matter and energy. The analyses also showed that phytoplankton richness and productivity (nutrients) were unimodally related and that the role of nitrogen was stronger than that of phosphorus in driving phytoplankton diversity in Danish lakes. Temporal analyses of 17 lakes, which were intensively monitored for 20 years, revealed synchronous changes in climate as well as in lake physico-chemical variables and plankton communities. Synchronous temporal changes in climate induced strong synchrony in lake physical variables (water temperature and stratifi cation) that are those most aff ected by the atmospheric energy fl ux. The synchrony in lake chemistry and plankton communities were stronger for lakes in recovery from earlier eutrophication, characterised by a strong decrease in phytoplankton biomass accompanied by enhanced water transparency as well as a change in the phytoplankton community composition from Chlorophyta dominance towards more heterogeneous communities with an increase in the richness of both plankton groups. A common increasing trend in plankton richness was observed across all lakes, coinciding with positive trends in temperature and precipitation as well as negative trends in wind speed, total nitrogen, NO3 and PO4 concentrations. Environmental control was not the only factor determining the plankton assembly in these 17 lakes. There was also signifi cant congruence between phyto- and zooplankton genera richness and community composition, even to a greater extent than that driven by their environmental relationships. This indicated that trophic interactions may also infl uence the plankton community assembly and positively aff ect the diversity of both groups. The strength of congruence weakened in highproductivity lakes, suggesting that the trophic coupling between plankton groups weakens with eutrophication, most likely because of high predation pressure on zooplankton due to high abundance of planktivorous fi sh in eutrophic lakes. Two events during the lake monitoring period enabled us to examine the cascading eff ects of the changes occurring at higher trophic levels on phyto- and zooplankton communities. Lake Engelsholm was subject to biomanipulation in 1993; large amounts of planktivorous fi sh were removed from the lake to help recovery from eutrophication. An immediate eff ect was evident, the phytoplankton biomass decreased 10-fold indicating a released predation pressure on zooplankton. Trophic interactions between phyto- and zooplankton favoured the diversity of both groups. The second event was the invasion of zebra mussels (Dreissena polymorpha) to Lake Faarup in 1993. The invasion also resulted in a decrease in the phytoplankton biomass; however, the eff ect was more gradual and the shift occurred with a four-year delay, refl ecting the time needed for zebra mussels to establish in the system. The invasion resulted in a decrease in the diversity of both phyto- and zooplankton, probably refl ecting selective plankton feeding by the zebra mussels. Overall, the analyses in this thesis refl ect the complex nature of community assembly. The assembly of forest birds and plankton communities was strongly driven by environmental conditions. However, the local communities were also linked with the regional populations, with some evidence also for dispersal-related effects, and their assembly was strongly infl uenced by ecological interactions across trophic levels. Therefore, the interactions between environmental species sorting, dispersal and complex biotic interactions at diff erent scales need to be further elucidated to obtain a better understanding of community assembly. Furthermore, studies aimed at understanding community response to global changes such as climate or habitat degradation should not only focus on the species direct response to the changing environment in isolation, but also include the potentially complex interactions among species as well as processes acting at regional scale.
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