Diversitätsmuster und Artenkomposition entlang von Stressgradienten in der Helgoländer Gezeitenzone.


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Markus.Molis [ at ] awi.de

Abstract

Diversity is affected by a variety of biotic and abiotic factors. To predict and appreciate how diversity is changing along various stress conditions an environmental stress model (ESM) (Menge & Sutherland) has been developed 20 years ago. Since then it has been adjusted to recent results of studies for a more accurate evaluation, concerning the pattern of diversity along stress gradients. For this model a unimodal graph is expected for diversity following a physical stress gradient. Weak competitors who are adapted to extreme conditions are responsible for the low diversity at high stress conditions, while the low diversity at low stress is a result of competitive exclusion of dominant species. We tested the ESM on three rocky shores differently exposed to wave action on Helgoland Island, Germany in a mensurate field experiment. Former research investigating the ESM in the rocky intertidal on Helgoland has not met the expectations of the ESM completely. To determine whether the ESM doesn't apply for Helgoland or if the experimental design lacked precision we altered the design to a higher vertical resolution of samples. We were taking samples from the beginning of May to mid June 2010. To be able to also adress biotic factors in our study we measured species composition besides diversity, species richness and evenness of macrobenthic organisms. On none of the three studied shores we could find a characteristic unimodal graph for the diversity along an environmental stressgradient accordingly to Menge & Sutherland (1987). However at the protected shore we observed an increase of diversity from high to low stress. The missing decrease of diversity in the lower eulittoral, is a result of the high density of microhabitats formed by macroalgae. Furthermore, we detected a connection between the patterns of diversity and wave exposure. Thus the observed diversity-pattern becoming flatter with an increase in wave exposure. A comparison of the diversity in two unlike habitats at the same shore aroused the consideration that abiotic factors might have different impacts on two different positions at the same shore. Concluding we found that the identity of species is important to comprehend the pattern of diversity following an environmental stress gradient. The ESM doesn't include this factor adequately and is therefore not a universal model applicable on all coasts. This is why we suggest that the ESM needs further development especially concerning biotic factors.



Item Type
Thesis (Bachelor)
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Peer revision
Not peer-reviewed
Publication Status
Published
Eprint ID
31825
Cite as
Bollen, M. (2010): Diversitätsmuster und Artenkomposition entlang von Stressgradienten in der Helgoländer Gezeitenzone. , Bachelor thesis, University Bremen.


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