University of Groningen
Herbivore-mediated structural diversity of vegetation
Ruifrok, Jasper Laurens
IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to
cite from it. Please check the document version below.
Document Version
Publisher's PDF, also known as Version of record
Publication date:
2014
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):
Ruifrok, J. L. (2014). Herbivore-mediated structural diversity of vegetation Groningen: s.n.
Copyright
Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the
author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).
Take-down policy
If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately
and investigate your claim.
Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the
number of authors shown on this cover page is limited to 10 maximum.
Download date: 18-06-2017
Propositions/Stellingen:
1. The success of using herbivores as a tool to create and maintain structural diversity in the
vegetation depends strongly on herbivore body size, abiotic heterogeneity in the soil and
fluctuations in herbivore density in time and space (this thesis).
2. Small mammalian herbivores promote structural diversity of the vegetation under a more
relaxed set of conditions than larger herbivores (this thesis, chapter 2).
3. Herbivores are more likely to positively affect structural diversity of the vegetation in the
presence of abiotic heterogeneity, such as in soil oxygen, soil moisture, soil acidity or soil
salinity (this thesis, chapters 2 & 3).
4. Fluctuations of herbivore density (e.g. due to populations crashes) in time and space and
space (e.g. due to migrations and temporal inaccessibility) positively affect structural
diversity of the vegetation because:
a. a heterogeneous lawn-rough mosaic is then more likely to be maintained (this
thesis, chapter 2)
b. tree recruitment is enhanced during periods of low herbivore density (this thesis,
chapter 3 & 5)
c. grazing lawns that are created during periods of high herbivore density promote
woody species establishment during periods of low herbivores (this thesis, chapter
5)
5. A predator community consisting of mesopredators (e.g. fox) and large predators (e.g.
wolf) can generate strong fluctuations in density of small and large herbivores (this
thesis, chapter 6), which in turn may generate periods that favor tree recruitment.
Whether wolves would indeed generate such periods of enhanced tree recruitment in the
Oostvaardersplassen would need empirical testing.
6. Herbivores can be introduced as a management practice to create and maintain structural
diversity in the vegetation and plant species richness (this thesis chapter, 2 - 5), but only
under the right range of conditions. However, herbivores can also be introduced for their
own social and ecological value.
7. PhD candidates in the Netherlands should keep their status as employee (AIO) instead of
receiving a scholarship (bursary students).
8. Science would be more efficient, useful and fun if there would be more emphasis on the
accomplishments of the group rather than of the individual, and if more time is spend on
quality teaching and communication instead of on publications.