Michael Clinchy

Post-Doctoral Fellow

Ph.D., University of British Columbia, 1999
M.Sc., Queen's University, 1990
B.Sc., University of Toronto, 1988

Department of Zoology
University of Western Ontario
London, Ontario, N6A 5B7

Phone: (519) 850-2533
FAX: (519) 661-2014


Curriculum Vitae

Research Interests

Possum Links (PhD Thesis, demographic model)

Clinchy, Haydon & Smith Simulations

Selected Publications

Curriculum Vitae

C.V. in PDF (Adobe Acrobat) format

C.V. and website last updated December 7, 2001

Research Interests

Current Research

Synergistic effects of food and predation on the physiological ecology of songbirds

Numerous studies have shown that animals balance the risk of predation against time
spent foraging.  Synergistic effects of food and predation on demography ought to be
the norm if such individual-level phenomena have population-level consequences.
Nonetheless, since population-level experiments on terrestrial vertebrates are rare,
and bifactorial experiments are rarer still, synergistic effects of food and predation on
demography have only recently been shown in mammals and have never before been
demonstrated in birds.  Over the past 2 years I have been collaborating with
Prof. L.Y. Zanette (U. Western Ontario) in conducting a 4-year, 2x2, manipulative
food addition plus natural predator reduction experiment on 14 populations of
Song Sparrows (Melospiza melodia).  Our results provide the first evidence of
synergistic effects in birds: territories subject to the combined food addition + low
predator treatment produced 1.5 times more young per season than would be
expected if the effects of food addition and predator reduction were independent
and additive.  This synergistic effect is similar in magnitude to those (1.5-1.9 > additive)
recently shown in mammals.

Prof. R. Boonstra (U. Toronto), a principal investigator on both of the recent mammal
studies, hypothesized that the individual-level mechanism responsible may be the
physiological stress effects induced by protracted hunger and chronic risk of predation.
Unfortunately, this hypothesis could  not be fully evaluated before the termination of the
earlier experiments.  The Song Sparrow experiment thus provides a unique opportunity
to address this hypothesis.

This research unites my expertise with Prof. Boonstra’s.  We are collaborating with
Prof. Zanette and Prof. J.C. Wingfield (U. Washington), the world’s leading expert on
physiological stress in songbirds, in comparing the levels of stress experienced by adult
and nestling Song Sparrows subject to each of the four experimental treatments
(high predator, unfed; high predator, fed; low predator, unfed; low predator).  Stress
levels are quantified by measuring corticosterone, glucose, and free fatty acid
concentrations in blood samples.  The consequences of chronic stress should be
reflected in anaemia (poor condition), low white-blood-cell counts (impaired immunity),
lower body weight, lower fecundity, greater fluctuating asymmetry(developmental
anomalies) in offspring, and poorer offspring survival.

Ph.D. Research

Does immigration "rescue" populations from extinction?

Metapopulation dynamics theory has grown by leaps and bounds in recent years.
Metapopulation models suggest that immigrants often help "rescue" populations from
extinction.  This is one of the primary rationales behind movement corridors for
conservation.  Metapopulation dynamics are generally inferred from the presence and
abundance of a target species in a survey of suitable habitat patches.  Such surveys
rarely include basic demographic data such as sex ratio and age structure, and do not
attempt to measure immigration directly.

Working in collaboration with Dan Haydon and Andrew Smith, we have developed
simple stochastic models that simulate the effects of spatially correlated disturbances
affecting spatially clustered populations.  Such disturbances can generate patterns of
patch occupancy consistent with the "rescue effect", even though dispersal is not involved.
Similarly, patterns of patch occupancy consistent with the "rescue effect" are to be
expected in any taxa, such as mammals, where there is male-biased dispersal.  Males
are more likely to be found in isolated patches, and isolated patches consisting entirely
of males are obviously doomed to extinction.  All this indicates the necessity for a more
rigorous empirical approach to the study of metapopulation dynamics, involving
direct measurements of the actual contribution of immigration to recipient population
dynamics in the field.

I am presently completing a series of papers reporting results from a spatially and
temporally replicated removal experiment conducted on common brushtail possums
(Trichosurus vulpecula), in a landscape with no physical barriers to dispersal.
I chose the common brushtail possum as a 'model' medium-sized marsupial herbivore.
Among mammals, Australia's medium-sized marsupial herbivores have been by far
the most adversely affected by recent human disturbance.  Australian species
account for roughly half of all mammalian extinctions in the past 200 years.  More
than one-third of all studies on mammals cited in a recent review on the efficacy of
movement corridors for conservation involved presence/absence surveys of
Australian marsupial possums and gliders.  Yet, my results show that even when
movements of only one home range length (about 200 m) are defined as dispersal,
immigration contributes only 1 % to the growth rate of recipient populations.
Parentage analysis using microsatellite DNA indicated that almost all daughters
settled on or adjacent to their mother's home range.  My results suggest that
presence/absence surveys do not provide sufficient evidence as to whether or not
immigration "rescues" populations from extinction.

Radio-collared adult female common brushtail possum (Trichosurus vulpecula)

Possum Links

Model of possum demography in XLS (Microsoft Excel 97) format

Clinchy (1999, Ph.D. thesis) in PDF (Adobe Acrobat) format

Clinchy, Haydon & Smith Simulations

This document provides the source code for the simulations discussed
in Clinchy, Haydon & Smith (Pattern does not equal process: what does
patch ocupancy really tell us about metapopulation dynamics?)

Clinchy, Haydon and Smith Source Code in PDF (Adobe Acrobat) format

Selected Publications

Clinchy, M., Krebs, C. J. and Jarman, P. J.  2001.  Dispersal sinks and handling effects:
     interpreting the role of immigration in common brushtail possum populations.
     Journal of Animal Ecology, 70:  515-526.

1.  An evaluation of the potentially adverse effects of measurement must be made before
     concluding that one is dealing with a 'dispersal sink'.
2.  We conducted a spatially and temporally replicated removal experiment on common
     brushtail possums (Trichosurus vulpecula) in uniformly suitable old-growth eucalypt
     forest in south-eastern Australia, that was designed to address the question: does
     immigration 'rescue' populations from extinction?
3.  Despite taking precautions to minimize potential harm, analyses indicated some
     evidence of an adverse effect of handling on the survival of pouch-young and strong
     evidence of effects on adult survival.  In addition, symptoms of stress associated with
     handling observed at our site, corresponded to symptoms reported in connection with
     the long-term (15 + years) trapping study on possums conducted by Efford et al. in the
     Orongorongo Valley (OV) of New Zealand.
4.  Initial projections from a demographic model indicated that the resident population
     at our site was not replacing itself (births < deaths), suggesting that the site was a
     dispersal sink.  This was inconsistent with the fact that the site was in prime habitat.
     Moreover, the measured rate of true immigration in response to experimental removals
     was not sufficient to maintain the population density.  Using data from Efford (1998),
     our model confirmed his suggestion that the OV site also appears to be a dispersal
     sink for possums, despite being in prime habitat.
5.  When otherwise undiagnosable deaths among adults were assumed to be due to
     handling and 'right-censored' (excluded), the projection was that the resident
     population at our site was stable (r = 0), and therefore not in need of 'rescue' by
     immigration.  Similarly, when survival estimates for the OV site were corrected by
     the same amounts, the projection was that the population at that site was also stable.
6.  Most vacancies created by our experimental removals were filled by neighbouring
     residents that expanded their ranges into the removal areas.  We suggest that the
     artificial 'removal' of residents as a consequence of deaths due to handling, may often
     induce an influx of such apparent immigrants, thereby giving the impression that
     immigration is 'rescuing' populations from extinction.

Clinchy, M., Haydon, D. T. and Smith, A. T.  2001.  Pattern does not equal process:
     what does patch occupancy really tell us about metapopulation dynamics?
     American Naturalist, accepted for publication September 2001.

Patch occupancy surveys are commonly used to parameterize metapopulation models.
If isolation predicts patch occupancy this is generally attributed to a balance between
distance-dependent re-colonization and spatially independent extinctions.  We investigated
whether similar patterns could also be generatedby a process of spatially correlated
extinctions following a unique colonization event (analogous to non-equilibrium processes
in island biogeography).  We simulated effects of spatially correlated extinctions on patterns
of patch occupancy among pikas (Ochotona princeps) at Bodie, California, using randomly
located ‘extinction discs’ to represent the likely effects of predation.  Our simulations
produced similar patterns to those cited as evidence of balanced metapopulation dynamics.
Simulations using a variety of disc sizes and patch configurations confirmed that our results
are potentially applicable to a broad range of species and sites.  Analyses of the observed
patterns of patch occupancy at Bodie revealed little evidence of ‘rescue effects’ and strong
evidence that most re-colonizations are ephemeral in nature.  Persistence will be
overestimated if static or declining patterns of patch occupancy are mistakenly attributed to
dynamically stable metapopulation processes.  Consequently, simple patch occupancy
surveys should not be considered as a substitute for detailed experimental tests of
hypothesized processes, particularly when conservation concerns are involved.

Johnson, C. N., Clinchy, M., Taylor, A. C., Krebs, C. J., Jarman, P. J., Payne, A.,
     and Ritchie, E. G.  2001.  Adjustment of offspring sex ratios in relation to availability
     of resources for philopatric offspring in the common brushtail possum.  Proceedings
     of the Royal Society of London, Series B, 268: 201-205.

The Local Resource Competition (LRC) hypothesis predicts that where philopatric
offspring compete for resources with their mothers, offspring sex ratios will be biased in
favour of the dispersing sex. This should produce variation in sex ratios among populations
in relation to differences in the availability of resources for philopatric offspring. However,
previous tests of LRC in mammals have used indirect measures of resource availability,
and have focussed on sex ratio variation among species or individuals, rather than local
populations. Here we show that the availability of den sites predicts the offspring sex ratio
in populations of the common brushtail possum. Female possums defend access to dens,
and daughters but not sons occupy dens within their mother's range. However, the
abundance of possums on our study areas was determined principally by food availability.
Consequently, in food-rich areas with high population density the per capita availability of
dens was low, and the cost of having a daughter should have been high. This cost was
positively correlated with male biases in the sex ratio at birth.

Clinchy, M.  1997.  Does immigration "rescue" populations from extinction?
     Implications regarding movement corridors and the conservation of mammals.
     Oikos, 80: 618-622.