Download Stage proposal

Master thesis Proposal
Timothée Carnus, M2 EBE
Supervisors: Alvin Helden, UCD School of Biological and Environmental Sciences, Belfield
Dublin 4 email: [email protected]
John Connolly, UCD School of Mathematical Sciences, Belfield Dublin 4
email: [email protected]
John Finn, Teagasc Research Centre, Johnstown Castle, Co Wexford
email: [email protected]
The idea that more diverse systems are more productive and more stable is of direct relevance
to agriculture. In short, are species mixtures more beneficial than less complex assemblages
such as those found applied in the majority of the more intense agricultural production
systems? This question is being studied with particular reference to grass sward productivity,
stability and nutrient use, within the context of a multi-country project: COST action 852. The
experiments are specifically testing the underlying ecological concepts (at the plant
interaction level) of the diversity/ecosystem function relation (i.e. greater diversity provides
higher productivity, better resistance to invasion and more efficient nutrient use). This study
proposes to use the results of a novel experimental design and statistical modelling (RGRDConnolly & Wayne, 2005) which disentangles the different contributions of species identity,
functional group diversity, species richness and relative abundance in particular. The
experiment focuses on the implications of evenness of species by systematically varying the
relative abundance of different species. This is a highly novel approach in diversity/function
studies, and has not been conducted in field experiments before now.
Firstly, this experiment has been set up to test various plant interaction hypotheses within the
context defined above. Secondly, an interest has developed in determining the extent of
arthropod diversity in agricultural landscapes and in their potential uses as indicators of land
management and diversity in general (Altieri, 1999; AgBiota, G. Purvis et al.). Therefore, in
view of this, it appears that making the link between sward diversity and insect diversity and
furthering the understanding of this potential link is important. How do more complex
mixtures affect insect communities on a local scale? Eventually, it would be feasible to
construct a model taking mechanistic processes into account to predict the outcome of the
experimental analysis following resource-consumer (plant, herbivore, predator) interactions.
The design of the experiment defines the plant community structure and allows its modelling.
It should therefore be possible to follow its effect on other levels of diversity. The proposed
study will focus on the effect of plant community structure and diversity on aboveground
insect community structure (herbivores, predators and parasitoids). The study of this response
in the ecology of the arthropod population to plant community structure will try to elucidate
various aspects of this relation.
Arthropods were collected using a suction sampler in spring and in summer for the years 2004
and 2005. This data has been sorted to order (Diptera, Coleoptera, Araneae, Bugs,
Hymenoptera and Other) and the majority has been identified to species or family level. The
plant community data includes initial sowing frequencies of each species in each plot,
biomass, (incidence of invasives, relative abundance of the four plant species in 2004 and
2005,). There is also as set of data on insect communities of neighbouring fields and field
margins for possible extrapolation.
Models generally predict an increase in insect diversity with an increase in plant species
diversity due to the increase in resource diversity (e.g. Lawton, 1978, Tilman, 1986). Whereas
a number of empirical studies confirm this prediction and have shown the importance of
taxonomic plant diversity in determining herbivore and higher trophic level insect diversity
(Siemann, 1998), an understanding of the underlying mechanisms has been elusive. Taking
into account functional group significance in determining host plant-insect interaction has
provided some insight (Symstad et al., 2000) as has taking a landscape-scale diversity
approach (Schweiger et al. 2005), but questions remain as to which effects are more important
on a local scale (Perner et al., 2005).
It will be assumed that the insect communities are at a dynamic equilibrium. The disturbance
created by the regular cutting of the sward will in fact simulate “natural” export of biomass in
an agro-ecosystem (silage cutting or large herbivore), while fertiliser input will mean the
system isn’t entirely deficient.
Hypotheses:

The structure of the plant community in terms of species evenness has an effect on
primary production, and thence indirectly on arthropod community structure and
diversity. The response is likely to be quite complex. The design of the experiment is
limited to only 4 plant species from 2 functional groups, the patterns observed in the
insect response will also be related to herbivore functional groups. For example, in
plots dominated by clover, weevils are more likely to be present, while the plots
dominated by grass will most likely contain leafhoppers.

Species evenness will play a role in the success of “unplanned” diversity through its
hypothesised local effect on invasion. This will also have an indirect effect on the
insect community (i.e. plant diversity remains constant therefore the insect community
has more time to adapt specifically to the resources present)

Host plant-insect interactions can be very specific (ie one plant  one insect). This
will vary according to the age of the community and the amount of disturbance under
which it evolves. But will the structure and diversity of the arthropod contingent vary
proportionally to plant species evenness?

Mechanisms determining insect community assemblage are intrinsic to plant
community supporting it. In the case of this experiment, the insect species will be
disturbance-withstanding species or early colonisers, “r-strategists”, and therefore
more generalist than one would expect to find in a natural, undisturbed grassland
ecosystem. This implies that arthropod community diversity and structure will not
only be dependant on the diversity of the plot (species and evenness elements) but
rather on diversity of the surrounding landscape. However, if we assume that plant
diversity effects are local effects, then even though the diversity of the landscape will
define the available pool of insect diversity, the plot level plant assemblages will
determine the small scale effects. Indeed, we can predict that different feeding
“guilds” out of r-strategists will be distributed according to the diversity variable.

These grassland arthropod communities are dominated by predators in the form of
spiders, as well as specific parasitoid Hymenoptera (there are exceptions). Looking
specifically at Araneae species is it possible to make assumptions of top-down,
bottom-up or ratio dependent control of community diversity? Are other
groups/species better indicators of insect community structure (eg herbivorous)?

Because they are generalists and need plant architecture to suit the construction of
their web, spiders are largely dependant on grassland structural diversity rather than
species diversity (competition? Exclusion? Etc.). Their diversity is not expected to be
directly correlated with plant diversity. Will it be correlated to herbivore diversity and
thence indirectly with plant diversity? Will plant evenness have an effect on the
structures available to spiders and hence on their diversity?
This Master’s thesis corresponds to the preamble to a PhD study of an experimental
investigation into the insurance hypothesis (exposed in slightly more detail at following web
page: http://www.teagasc.ie/johnstowncastle/fellowship12.htm)
References:
Altieri (1999) The ecological role of biodiversity in agricultural ecosystems. Agriculture
Ecosystems and Environment, 74, 19-31.
Connolly, J. & Wayne, P. (2005) Assessing determinants of community biomass composition
in two-species plant competition studies. Oecologia, 142, 450-457.
Lawton, J. H. (1978) Host-plant influences on insect diversity: the effects of space and time.
In: Mound, L. A. & Waloff, N. (eds), Diversity of insect faunas. Blackwell, pp.105–125.
Perner, J.,Wytrykush, C., Kahmen, A., Buchmann, N., Egerer, I., Creutzburg, S., Odat,
N., Audorff, V. & Weisser, W. W. (2005) Effects of plant diversity, plant productivity
and habitat parameters on arthropod abundance in montane European grasslands.
Ecography, 28, 429-442.
Siemann, E. (1998) Experimental tests of effects of plant productivity and diversity on
grassland arthropod diversity. Ecology, 79, 2057-2070.
Schweiger, O., Maelfait, J. P., Wingerden, W., Hendrickx, F., Billeter, R., Speelmans, M.,
Augenstein, I., Aukema, B., Aviron, S., Bailey, D., Bukacek, R., Burel, F., Diekötter, T.,
Dirksen, J., Frenzel, M., Herzog, F., Liira, J, Roubalova, M. & Bugter, R.(2005)
Quantifying the impact of environmental factors on arthropod communities in agricultural
landscapes across organizational levels and spatial scales. Journal of Applied Ecology, 42,
1129-1139.
Symstad, A. J., Siemann, E. & Haarstad, J. (2000) An experimental test of the effect of plant
functional group diversity on arthropod diversity. Oikos, 89, 243–253.
Tilman, D.(1986) A consumer-resource approach to community structure. Am. Zool. 26, 5–22.
Selected Publications:
Ramseier, D., Connolly, J. & Bazzaz, F.A. (2005) Carbon dioxide regime, species identity
and influence of species initial abundance as determinants of change in stand biomass
composition in five-species communities: an investigation using a simplex design and RGRD
analysis. Journal of Ecology, 93, 502-511.
Hassall, M., Helden, A., Goldson, A. & Grant, G. (2005) Ecotypic differentiation and
phenotypic plasticity in reproductive traits of Armadillidium vulgare (Isopoda: Oniscidea).
Oecologia, 143, 51-60.
Helden, A.J. & Leather, S.R. (2004) Biodiversity on urban roundabouts – Hemiptera,
management and the species-area relationship. Basic & Applied Ecology, 5, 367-377
Finn, J.A. & Gittings, T. (2003) A review of competition in north temperate dung beetle
communities. Ecological Entomology, 28, 1-13.
Hassall, M., Helden, A. & Benton, T. (2003) Phenotypic plasticity and interpopulation
differences in life history traits of Armadillidium vulgare (Isopoda:Oniscidae). Oecologia,
137, 85-89.
Helden, A.J. & Dixon, A.F.G. (2002) Life-cycle variation in the aphid Sitobion avenae: costs
and benefits of male production. Ecological Entomology, 27, 692-701.
Finn, J.A. & Giller, P.S. (2002) Experimental investigations of colonisation by north
temperate dung beetles of different types of domestic herbivore dung. Applied Soil Ecology,
20, 1-13.
Finn, J.A. (2001) Ephemeral resource patches as model systems for diversity-function
experiments. Oikos, 92, 363-367.
Connolly, J. & Wachendorf, M. (2001). Developing multisite dynamic models of mixed
species plant communities. Annals of Botany 88, 703-712.
Connolly, J., Goma, H.C. & Rahim, K. (2001) The information content of indicators in
intercropping research. Agriculture, Ecosystems and Environment, 87, 191-207.
Connolly, J., Wayne, P. & Bazzaz, F.A. (2001) Interspecific Competition in plants: how well
do current methods answer fundamental questions? The Am. Nat., 157, 107–125.
Finn, J.A. & Giller, P.S. (2000) Patch size and colonisation patterns: an experimental analysis
using north temperate coprophagous dung beetles. Ecography, 23, 315-327.
Wayne, P.M., Carnelli, A.L., Connolly, J. & Bazzaz, F.A. (1999) The Density-Dependence
of Plant Responses to Elevated CO2: Stand-Level Productivity. Journal of Ecology, 87, 183192.
Finn, J.A., Gittings, T. & Giller, P.S. (1998) Aphodius dung beetle assemblage stability at
different spatial and temporal scales. Applied Soil Ecology, 10, 27-36.
Connolly, J. (1997) Substitutive experiments and the evidence for competitive hierarachies in
plant communities. Oikos, 80, 179-182.
Connolly J. & Wayne P .(1996) Asymmetric competition between plant species. Oecologia,
108, 311-320.