Many plant and animal species modify the habitat they live in with the aim to increase the suitability of their habitat for growth, reproduction and survival. Examples are beavers that construct dams, rabbits that dig holes, ants and termites that construct large mounds or earthworms that tunnel in soil. However, the changes they make in the physical state of their surroundings by building or tunneling also affects other species that co-occur with these so-called ecosystem engineers (EE). This makes EE very important organisms in ecosystems due to their often strong indirect and long-lasting effect on other community members. Their impact on community members is often larger than effects by competition or predation.
An important EE in salt marshes is the litter-feeding and bioturbating landhopper Orchestia gammarellus. Basically, this amphipode species of about 1.5 cm in body size acts as the earthworm of the salt marsh. Landhoppers dig into the soil to escape extreme climatic events, which results in a structured soil with an increase in pore space. In soils that are compacted due to trempling by large herbivores, the presence of O. gammarellus is important as it decompacts the soil due to bioturbation and, subsequently, increases soil aeration and water infiltration into the soil. This has beneficial effects on plant growth, but might also influence the abundance, diversity and functional composition of other soil fauna groups. It has been shown that the presence of other EE, such as muscle beds and sea grass beds on mud flats has a positive effect on the diversity of small invertebrates. Likewise, it is believed that the increase in soil structure and change in pore size distribution will affect small invertebrates, such as springtails and moss mites, that cannot bioturbate the soil and have to rely on the habitat modifications made by O. gammarellus.
The aim of this internship is to assess if presence of O. gammarellus indeed increases the diversity and abundance of springtails and mites, and if a relationship exists between changes in pore size distribution and the body size distribution of soil animals.
- Conduct analyses on animal community composition and body size distribution in field samples collected from areas with high and low soil compaction (i.e. grazed and non-grazed areas).
- Use NMRI techniques and digital image analysis to measure pore size distribution in soils as a function of the level of soil compaction due to trampling by large herbivores.
- Use statistical software to link body size distribution of soil animals to pore size distribution in compacted and non-compacted soils.
- Learn appropriate techniques to sample and identify soil fauna species.
- Use and learn basic methods in image analysis to analyze body size and pore size distribution.
- Maintain organized and consistent lab notebook and data management scheme.
Location and Timeframe
- Lab work will be conducted at the Vrije University, Amsterdam. Field work will be conducted at the salt marsh of the Island of Schiermonnikoog, in the northern part of The Netherlands.
- The Vrije Universiteit has a fully-equipped field station on the island, which allows for long stays on the island.