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Interaction strength in an intertidal rocky habitat: an observational approach

Heij, M.E. de (1999) Interaction strength in an intertidal rocky habitat: an observational approach. Master's Thesis / Essay, Biology.

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Abstract

Knowing the structure of the food web within a community is of specific importance for the understanding of the dynamics of a community, which can lead to better predictions on how the system will react on (environmental) changes. For each combination of two species related to each other as predator and prey, the total impact of the predator species on the prey species can be calculated. This 'species impact' can be quantified by multiplying the effect individual predators have on the (entire) prey population — i.e. the 'per capita interaction strength'- with the density of the predator population. The most common approach of studying interaction strength between species in a community has been an experimental one. Recently, an observational approach has been developed, as an experimental approach can not be applied for all predator-prey relations. The observational approach has originally been developed to study interaction strengths between shorebirds and their prey. In this study the feasibility of the observational approach to study the effect of a marine predator - the starfish Pisaster ochraceus - has on various prey species of an intertidal rocky shore community is tested. Results show that Pisaster feeds selectively upon mussels even though other prey species are available. Acorn barnacles are avoided when possible or eaten in relation to their abundance. At the two sites tested Pisaster has a stronger per capita effect upon the mussel population than on the acorn barnacle population; other prey species remained more or less unaffected by the predation activity of the starfish. The predator has a stronger per capita effect upon the mussel population than on the barnacle population. In comparison with a previous study on the same species, the 'per capita effect' and 'species impact' were surprisingly low. Even though the starfish has proven to be a 'keystone species', the effect of the starfish on the prey population found ii this study was only comparable with that of a weak predator. The feasibility of the observational approach is discussed and it is indicated for which parameters more experiments are required before the observational approach can be used for this starfish.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Biology
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 07:44
Last Modified: 15 Feb 2018 07:44
URI: http://fse.studenttheses.ub.rug.nl/id/eprint/9434

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