Robert Lenthall Jefferies Collection

Permanent URI for this collection

https://hdl.handle.net/10315/9274

When Bob Jefferies died unexpectedly in 2009, Canada lost one of its most important Arctic biologists at a vital and significant time. Bob was a professor at the University of Toronto from 1974 to 2009 in the Botany Department, which later became the Ecology and Evolutionary Biology Department.

This sub-community in the Churchill Communities of Knowledge digital archive celebrates Bob's life and research legacy. From 1978 to 2009, Bob and his students carried out field research on the effects of herbivory on salt-marsh vegetation by lesser snowgeese at La Pérouse Bay, on the shores of Hudson Bay, east of Churchill, Manitoba. Bob is seen above, at Camp Finney (Nestor 2) during spring melt in June 1983. Bob also did research with his students in other parts of the Churchill region, and elsewhere in the Arctic.

Bob not only worked in northern Canada. He carried out research in California, where he was a post-doc with Emmanuel Epstein, at University of California at Davis, from 1962-64, and a Distinguished Visiting Professor at the Bodega Marine Laboratory (UC Davis) in 2002-03. Bob also studied salt-marshes in the United Kingdom and Europe.

Digitized versions of many of Bob's research accomplishments can be found in this collection, including his students' theses and dissertations, along with images and other forms of media.

Correspondence and information relating to Bob's participation in the Intergovernment Panel on Climate Change is also lodged here.

The programme from Bob's Memorial Celebration, held on November 9th 2009, can be found here

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Now showing 1 - 20 of 52

Open Access
A comparison of the growth responses of three sedges to foraging by lesser snow geese.
(1987) Kotanen, Peter M.
SUMMARY:
Open Access
A day off from field work, at Knight's Hill esker, near Churchill on Hudson Bay, Manitoba, Canada.
(1981) Bazely, Dawn R.
Open Access
A Remembrance and Celebration of the Life of Robert Lenthall Jefferies
(University of Toronto, 09/11/2009)
Open Access
Allochthonous inputs: integrating population changes and food-web dynamics
(Elsevier, 2004) Jefferies, Robert L.
Most ecosystems are recipients of allochthonous materials that enhance in situ productivity. Recent theoretical and empirical studies suggest that low to moderate inputs can stabilize food webs. However, depending on the trophic levels that use the resource, food webs can become unstable as inputs increase. Where large amounts of agricultural resources are transferred to natural habitats, trophic dynamics change: trophic cascades can occur and rare or uncommon species can become invasive. Rates of change in species abundances can also be amplified by the effects of changes in legislation and management practices on subsidized consumers.
Open Access
Burning garbage at Camp Finney (Nestor 2), La Pérouse Bay, Hudson Bay, Churchill, Manitoba, Canada, 1983.
(Jul-83) Bazely, Dawn
Open Access
Collection of e-mails sent from friends and colleagues of Dr. Robert L. Jefferies (Bob) with their reaction to his sudden death
(08/01/2012)
Open Access
Curriculum Vitae
(2011-07-27T14:54:48Z) Jefferies, Robert L.
Open Access
Dawn Bazely digging drainage ditches at Camp Finney
(Jun-84) Bazely, Dawn R.
Open Access
Dr. Robert L. Jefferies (Bob) at the Camp Finney (Nestor 2 site), La Pérouse Bay, Hudson Bay, Manitoba, Canada during spring melt.
(Jun-83) Bazely, Dawn R.
Open Access
Early spring (June) field work on the La Pérouse Bay salt marsh, Hudson Bay, Manitoba, Canada.
(Jun-81) Bazely, Dawn
Open Access
Experimental studies of the effects of grazing by captive goslings of the lesser snow goose on the vegetation of a subarctic salt marsh.
(1988) Hik, David S.
SUMMARY:
Open Access
Free amino acids in Arctic salt-marsh coastal sites and plant nitrogen acquisition
(Ottawa : National Library of Canada = Bibliothèque nationale du Canada, 2004) Henry, Hugh A.L.
The importance of free amino acids as a source of plant nitrogen was examined in an Arctic coastal salt-marsh. Concentrations of inorganic nitrogen in salt-marsh soils were low relative to those reported for most temperate soils, whereas soluble organic nitrogen concentrations of salt-marsh soils were relatively high; the median ratio of free amino acid nitrogen as a proportion of ammonium nitrogen was 0.36 and amino acid concentrations exceeded those of ammonium in 24% of samples. Growth of the salt-marsh grass 'Puccinellia phryganodes' on glycine in a continuous flow hydroponic medium was similar to growth on ammonium ions at an equivalent concentration of nitrogen. Furthermore, in short-term excised root uptake experiments, rates of glycine uptake were equal to rates of ammonium and nitrate uptake combined when roots were provided with all three nitrogen substrates at equal concentrations. Amino acid uptake relative to ammonium uptake was favoured at high temperatures, high salinity and low pH. Free amino acids turned over rapidly in the soil, with half-lives in the soil solution ranging from 8-23 h for glycine, compared with ranges of 6-15 h and 6-16 h for ammonium and nitrate ions, respectively. Plant incorporation of 15N tracer injected into soil cores was 56, 83, and 68% of incorporation by soil microorganisms for glycine, ammonium and nitrate ions, respectively. The simultaneous incorporation of 13C and 15N into plant roots following injection of 13C15N-glycine into soil cores indicated that at least a portion of this amino acid was absorbed intact. In a model of the dynamics of nitrogen movement in an Arctic salt-marsh grazed and grubbed by geese, the direct uptake of organic nitrogen by plant roots was required to obtain rates of mineralization consistent with empirical estimates. Overall, these results indicate that free amino acids are likely a substantial contribution to plant nitrogen nutrition in Arctic coastal marshes.
Open Access
Goose-induced Changes in Vegetation and Land Cover between 1976 and 1997 in an Arctic Coastal Marsh
(Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, 2005) Abraham, Kenneth F.; Jefferies, Robert L.; Rockwell, Robert F.
Since the 1970s, a breeding colony of lesser snow geese (Chen caerulescens caerulescens L.) at La Pérouse Bay, Manitoba, has grown 8% annually. This increase has led to significant loss of plant cover in all major salt- and freshwater coastal habitats between 1976 and 1997. A series of transects established in 1976 was resurveyed in 1997. Exposed sediment, extent and type of vegetative cover, and aquatic areas were recorded along transects using a classification of 12 a priori classes. Five regions within the colony were identified, and changes in vegetation cover differed among these and depended on unique combinations of vegetation class and year. Grubbing by geese has led to loss of graminoid plants, especially in intertidal and supratidal marshes. Exposed sediments have largely replaced previously vegetated areas since 1976. Species characteristic of disturbed sites have colonized exposed sediment with the most abundant species varying according to soil conditions. In intertidal marshes, willow cover declined in association with the development of hypersalinity after loss of the graminoid mat, but willow cover increased at the base of well-drained beach ridges and in a river delta with ample winter snow accumulation and freshwater flow in spring that protected ground vegetation. Most of the expected successional trends associated with isostatic uplift and changes in soil organic matter failed to occur because of intense goose foraging throughout the 20 years. The likelihood of sustained recovery of plant communities in the immediate coastal zone is very low, as long as goose numbers continue to increase. Indirect effects of vegetation loss (e.g., hypersalinity) and subsequent erosion of exposed sediments following grubbing will delay plant colonization and retard succession.
Open Access
In Memoriam - Jefferies was renowned Arctic scientist
(University of Toronto, 27/10/2009) Ferguson, Ailsa
Open Access
Is the decline of soil microbial biomass in late winter coupled to changes in the physical state of cold soils?
(Elsevier, 2010) Jefferies, Robert L.; Walker, Alan; Edwards, Kate A.; Dainty, Jack
During winter when the active layer of Arctic and alpine soils is below 0 °C, soil microbes are alive but metabolizing slowly, presumably in contact with unfrozen water. This unfrozen water is at the same negative chemical potential as the ice. While both the hydrostatic and the osmotic components of the chemical potential will contribute to this negative value, we argue that the osmotic component (osmotic potential) is the significant contributor. Hence, the soil microorganisms need to be at least halotolerant and psychrotolerant to survive in seasonally frozen soils. The low osmotic potential of unfrozen soil water will lead to the withdrawal of cell water, unless balanced by accumulation of compatible solutes. Many microbes appear to survive this dehydration, since microbial biomass in some situations is high, and rising, in winter. In late winter however, before the soil temperature rises above zero, there can be a considerable decline in soil microbial biomass due to the loss of compatible solutes from viable cells or to cell rupture. This decline may be caused by changes in the physical state of the system, specifically by sudden fluxes of melt water down channels in frozen soil, rapidly raising the chemical potential. The dehydrated cells may be unable to accommodate a rapid rise in osmotic potential so that cell membranes rupture and cells lyse. The exhaustion of soluble substrates released from senescing plant and microbial tissues in autumn and winter may also limit microbial growth, while in addition the rising temperatures may terminate a winter bloom of psychrophiles. Climate change is predicted to cause a decline in plant production in these northern soils, due to summer drought and to an increase in freeze-thaw cycles. Both of these may be expected to reduce soil microbial biomass in late winter. After lysis of microbial cells this biomass provides nutrients for plant growth in early spring. These feedbacks, in turn, could affect herbivory and production at higher trophic levels.
Open Access
Landscape view at Churchill, Manitoba, Canada, 1982.
(Aug-82) Bazely, Dawn R.
Landscape to the south of trail between Knight's Hill esker and launch, Churchill, Manitoba, Canada
Open Access
Lesser Snow Geese flying over salt-marsh flats at Moon La Pérouse Bay,1983.
(Jun-83) Bazely, Dawn R.
Lesser Snow Geese flying over salt-marsh flats at Moon La Pérouse Bay, Hudson Bay, Churchill, Manitoba, Canada.
Open Access
Letter from R.K. Pauchari, Chairman of the Intergovernmental Panel on Climate Change (IPCC), to Robert L. Jefferies acknowledging his contribution to the work which led to the Nobel Peace Prize awarded to the IPCC
(20/03/2008) R. K. Pachaur
Open Access
Letter to Dr. D.R. Bazely regarding the Jack Dainty Graduate Scholarship Fund
(08/01/2012) Jefferies, Robert L.; Harvey, Harold
Open Access
Michelle Kortnaar doing field work in the sub-arctic salt marsh of the Mast River Delta, at La Pérouse Bay, Hudson Bay, Canada
(Jun-81) Bazely, Dawn R.

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