Mature forest canopies worldwide sustain an enormous diversity of arthropods, many of which are specialist natural enemies. However, with the exception of species that exhibit massive outbreaks, host-specific canopy arthropods are thought to have relatively little influence on tree health and overall forest productivity. My thesis examines the role of one such arthropod in a temperate forest stand in central Ontario. The maple spindle gall mite Vasates aceriscrumena (Riley) (Acari: Eriophyoidae) is a host-specific canopy parasite that induces galls on leaves of sugar maple Acer saccharum Marsh. I examine three diverse topics related to this host-parasite system: 1) the seasonal phenology of this mite in mature sugar maple canopies, 2) the impacts of galling on host physiology and growth and 3) the distribution of this mite across host ontogeny and within the broader context of the local forest community. With respect to phenology, I document a previously unobserved interaction between the gall-inducer and a gall-invading mite (ubiquitous in the canopy but new to science) and consequences of this on the bionomics of galling mite populations. This work is also the first to examine differential physiological responses to galling across two distinct stages in the ontogeny of the host. Infected leaves in mature trees show drastic reductions in gas-exchange processes (photosynthesis, stomatal conductance and water use efficiency) while infected sapling leaves show no such detectible responses. Further, I find a significant negative correlation between radial increment growth in mature trees and levels of mite galling, as well as significantly increased galling frequency in mature trees compared with understory saplings. Finally, I explore the relationship between galling abundance and abiotic and biotic variables within a large mapped forest plot and show that gall densities are most strongly correlated with local species diversity and less so with host densities. Overall, my research provides a new perspective on the influence of host-specific, dispersal-limited canopy arthropods as major drivers of ‘age-dependent’ reductions in physiological performance and growth of older trees and as natural enemies that are strongly associated with local forest community distribution patterns.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/26314 |
| Date | 22 February 2011 |
| Creators | Patankar, Rajit |
| Contributors | Thomas, Sean C., Smith, Sandy |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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