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The impact of herbivores on the growth expansion of aquatic plants
and helophytes
General context
Riparian vegetation (e.g. reed belts) is an important habitat for breeding marsh
birds and it helps to improve water transparency through several mechanisms.
However, they are currently lacking or decreasing in many nature areas. As
several herbivores (greylag geese, muskrats, coots, crayfish) are becoming more
and more abundant in the Netherlands and all these species forage on
helophytes, it is often hypothesized that the lack of expansion of helophytes into
the water is caused by herbivory. However, evidence on the general applicability
of this hypothesis is lacking.
Project outline
With an exclosure experiment we will test the effect of herbivores on the
development of the helophyte zone and the growth of aquatic plants. In
collaboration with water boards, exclosures will be placed in several fen areas
that differ in herbivore density. You are welcomed to participate in this large
scale experiment.
Duration (indicative)
6-9 Months.
Contact
Judith Sarneel or Liesbeth Bakker, e-mail: [email protected] or
[email protected], tel.: +31 (0)317-473557.
Can Water Level Fluctuations increase biodiversity of the riparian zone?
General context
In a previous experiment we discovered that seeds and seedlings in shorelines
are often washed away by waves, resulting in a very low establishment. This has
large consequences for biodiversity of riparian zones (ditch banks, lake shores
etc.). Especially in the Netherlands, where water tables are strictly regulated as
seeds are then deposited (in winter) in the same zone as where the water and
waves will be in spring. A more natural regime, where the water table drops in
spring and remains low during summer could enforce a higher biodiversity in the
riparian zone. Namely, seeds and seedlings might be safer as the waves have a
lower probability to reach the seedlings that emerge from the seeds deposited in
winter. Besides, a fluctuating water regime will result in a wider ecotone, by
which the germination and growth requirements of more species and seeds are
met. This leads to the hypothesis that a flexible water table will enhance
biodiversity.
Project outline
In 10 areas in the Netherlands, the water level will be regulated less strict,
allowing more natural water level fluctuations due to evaporation and
precipitation. This provides an ideal testing situation of the hypotheses
mentioned above. Besides, a mesocosm experiment will be designed to test the
interaction between water level fluctuations and germination and establishment
experimentally. You are invited to participate in one of these challenging and
innovative projects.
Duration
3-9 months
Contact
Judith Sarneel or Liesbeth Bakker
E-mail: [email protected] or [email protected]
Tel. +31 (0)317-473557
Ecosystem functions of invasive submerged macrophytes
General context
Freshwater ecosystems experience an increasing number of exotic species. Also, the number of
freshwater macrophytes found in The Netherlands is increasing due to invasive newcomers. This is
generally considered as a threat for native biodiversity. However, some invasive species that have
been here for a longer time, such as Elodea nuttallii that is here for more than a century already,
are now valuable food for waterfowl and form a habitat for numerous macrofauna species and
shelter for fish. Also, there are problems in eutrophic lakes to maintain or bring back a macrophyte
vegetation. Submerged macrophytes have a positive effect on water transparency. As some
invasive species can be very abundant, the question is whether they also have positive effects on
water transparency and quality.
Project outline
In this project the question is what the effects of invasive submerged macrophytes are on water
quality, transparency and other biota, such as macrofauna, and how these effects compare to
native submerged plants. Several approaches are possible: a field study to sample native and
nonnative submerged plants, attached macrofauna and the water surrounding them. Additionally,
mesocosm experiments can be designed to grow the native and nonnative plants under increasing
nutrient loading and compare their effects on water chemistry and algal blooms. Finally, palatability
experiments can be done to test whether invasive plants are good food for fish, crayfish and snails.
Duration (indicative)
4-9 Months.
Contact
Liesbeth Bakker, e-mail: [email protected], tel.: +31 (0)317-473557.
Herbivory in aquatic omnivores
General context
Most aquatic herbivores that consume macrophytes are in fact omnivorous. As most animal food
contains higher nutrient concentrations than plants, the question is why they eat plants and under
which conditions. These conditions could be differences in nutrient concentration in the
environment. Plants grown in nutrient rich water have a higher nutrient concentration than plants
from nutrient poor water. Do grazers have a preference for plants with a higher nutrient
concentration relative to nutrient poor plants? Do they prefer animal food over plants even when
plants are nutrient rich? And do temperature, and thus food requirements and digestion efficiency
affect food preference? These are very basic questions, but little is known about herbivory in
aquatic omnivores so there is a lot to discover in this field of research.
Project outline
Food choice experiments with ducks and/or crayfish and/or fish are possible to test preference of
animal versus plant food and the importance of nutrient concentration in the food items. This
project will be in cooperation with dr. Martijn Dorenbosch.
Duration (indicative)
4-9 Months.
Contact
Liesbeth Bakker, e-mail: [email protected], tel.: +31 (0)317-473557.
Causes and consequences of herbivore diversity: a comparison
between aquatic and terrestrial ecosystems
General context
Diversity of herbivore communities may affect the effect of herbivores on plants. For example the
amount of plants grazed may differ among herbivore communities composed of different amounts
of species as different herbivores may have additive or compensatory effects on plants.
Traditionally, the composition and effects of herbivore communities has been studied separately for
different ecosystems. At the NIOO we started a project that investigates similarities in herbivore
community diversity and effects of these communities across aquatic and terrestrial ecosystems.
We specifically look at the role of food quantity and quality and dispersal efficiency for the
composition of herbivore communities in different systems.
Project outline
Field and indoor mesocosm experiments are possible with macrophytes grazed by macrofauna,
algae grazed by zooplankton, terrestrial plants grazed by insects and plant roots grazed by
nematodes.
For the macrophyte part of the project indoor experiments can be done where planted macrophytes
of different quality and abundance are grazed by herbivore assemblages which differ in species
richness. This project will be in cooperation with dr. Tibor Bukovinszky.
Duration (indicative)
4-9 Months.
Contact
Liesbeth Bakker, e-mail: [email protected], tel.: +31 (0)317-473557