Understanding the biodiversity-ecosystem function relationship: The effect of
specialist species on pollination efficiency
Soraya Villalobos, PhD student
Plant Biodiversity Laboratory, Department of Biological Science, University of
Calgary, Calgary (Alberta) Canada.
How do we prioritize species or areas for conservation? Species-rich sites may provide
more ecosystem function in terms of stability yet we know little about what features of
species-rich sites convey this increased ecosystem functioning (Cardinale et al 2000).
A common feature of plant-pollinator relationships in communities are to observe
a trend for very asymmetric interactions, where specialized plants are visited by
generalist insects and vice versa (Aigner 2001, Olesen & Jordano 2002). However for
reasons that are not yet clear, specialists are disproportionately present in communities
with high species richness, potentially because these communities foster more resource
partitioning. Information on whether pollinator species richness or increased pollinator
specialization offer enhanced fitness advantages to the plant community is not currently
available. This project aims to examine whether specialists (1) convey ecosystem
functioning; and (2) are replaceable by closely related species.
The features of communities that convey advantages in seed production can be
well characterized with new tools available from phylogenetics. The idea of a broad
generalization hypothesis has been mostly based on qualitative data with indirect
estimators of frequency rate and pollinator effectiveness. While previous studies indicate
that indirect measurements of interaction parameters as well as surrogates of
specialization are valid to study plant-pollinator assemblages (Ollerton et al. 2007), pairs
of reciprocal specialized species should be examined within the assemblage they interact
to form interaction network.
One reason why specialization traits and phylogenetic diversity have rarely been
related to pollination efficiency is that they require numerous samples with
spatiotemporal variability. The spatial variation in plant-pollinator interactions is
important to explain the role of pollinators as drivers of plant distribution, due to in
geographic context the environmental heterogeneity can influence the abundance and
patterns of pollinator visitations (Herrera 1988). However the effect of large-scale
geographical variation on plant-pollinator network and plant fitness across geographic
range is very often neglected from pollinator studies (Olesen and Jordano 2002). While
data exists on many networks most have occurred over a rather small spatial scale.
Published works that consider spatial variation are mostly focused on co-evolutionary
aspects of plant morphological variation instead of the nature and efficiency of the
pollinator process. Specifically across the Neotropics, most studies have been
concentrated in few countries and the data are truly too sparse to make solid conclusions
about spatial scale of variation and the ecological factors that underlie variation in
pollinator communities (Archer et.al., 2014).
The forest of Central America contains many species with severely restricted
natural ranges (Murphy and Lugo 1995) because they make up a corridor with flora and
fauna from two different ecozones: Nearctic (North America) and Neotropical (South and
Central America and the Caribbean islands). Specifically, Parque Nacional Cusuco
(PNC), a protected area in the northwest Honduras, is part of the Mesoamerica corridor
that encompasses several habitats with great diversity and high beta diversity framed
within large elevation rates and seasonal rainfalls. With such remarkable characteristics,
Cusuco provides the ideal scenario to assess the relationships between components of
species richness and plant-pollinator specialization.
This topic aims to build a quantitative flower-visitor network comparing real
estimates of plant-pollinator specialization within PNC. Dissertation students will have
the opportunity to ask many questions related to plant-pollinator assemblages (Bascompte
2009, Nuismer 2012). Projects could include 1) setting transects to register the
quantitative abundance of insect floral visitors per plant species and determining
interaction frequency among pairwise species, 2) capture floral visitors using insect nets,
pin specimens for taxonomical identification and recording biological attributes of plants
(e.g. symmetry, colour, size) and their floral visitors (body size, sociality). Additionally,
the plant-pollinator network reconstruction will allow students to address questions about
whether interaction matrices with a higher number of visitations resulted in increased
seed set.
Pinned and herbarium specimens will be sent to the University of Calgary to
determine their taxonomical category. Students will manage their own data and the data
collected for the entire plant-pollinator community as well. After the identification of
specimens, a phylogeny built with plant and visiting species list will be uploaded in a link
on the webpage of the plant biodiversity lab of the University of Calgary. Students will
be taught techniques in phylogenetics to analyse the plant-pollinator assemblages from
Honduras to determine what elements of species-rich communities convey ecosystem
functioning.
Literature cited
Aigner, P. A. 2001. Optimality modeling and fitness trade - offs: when should plants
become pollinator specialists? Oikos 95:177–184.
Archer, C. R., C. W. W. Pirk, L. G. Carvalheiro, and S. W. Nicolson. 2014. Economic
and ecological implications of geographic bias in pollinator ecology in the light of
pollinator declines. Oikos 123:401–407.
Bascompte, J. 2009. Mutualistic networks. Frontiers in Ecology and the Environment
7:429–436.
Cardinale B.J., Nelson K., Palmer M.A. 2000. Linking species diversity to the
functioning of ecosystems: on the importance of environmental context. Oikos 91: 175183.
Herrera CM (1988) Variation in mutualisms: the spatiotemporal mosaic of a pollinator
assemblage. Biol J Linn Soc 35:95–125
Murphy, P. And A.E. Lugo. 1986. Ecology of Tropical Dry Forest. Annual Review of
Ecology and Systematics 17: 67-88.
Nuismer, S. L., P. Jordano, and J. Bascompte. 2012. Coevolution and the architecture of
mutualistic networks: 338–354.
Olesen, J. M., and P. Jordano. 2002. Geographic patterns in plant–pollinator mutualistic
networks. Ecology 83 (9): 2416-2424.
Ollerton, J., Killick, A., Lamborn, E., Watts, S., & Whiston, M. 2007. Multiple meanings
and modes : on the many ways to be a generalist flower 56: 717–728.