Abstract
For ectotherms, environmental temperature is an important correlate of growth rate,
development time and final body size, with the dominant trend being an increase in growth
rate and a decrease in size at maturity as temperature increases. Approximately 99% of the
species on earth are ectothermic, relying primarily on external sources for their body heat.
Given the importance of body size in ecology and the desire to be able to forecast responses
to climate change, there is a need to understand the effects of temperature and diet on body
size in ectotherms, and how these environmental variables interact with genetic adaptation.
In this respect, the mountain stone weta Hemideina maori is a species of particular interest, as
it shows an increase in body size in both males and females, in association with increasing
altitude and decreasing temperature. Little is known about survival and longevity of H. maori
in its natural environment, but their relatively large size and flightlessness makes them an
ideal candidate for mark-recapture studies. This thesis aimed to: ( 1) examine potential
differences in the survival probability of adult alpine weta along an altitudinal and body size
gradient, using mark-recapture methodology; (2) determine the diet preferences of adult weta
at low, intermediate and high altitudes using vegetation quadrat surveys and faecal pellet
analysis and (3) use a common-garden experiment approach to determine whether variation
in body size could be attributed to variation in environmental temperature and/or genetic
adaptation.
Adult weta at high altitudes were significantly larger than at intennediate and low altitudes,
but there was no difference in monthly survival between weta at high and low elevation sites.
The 1nonthly survival probability of adult weta at the high and low elevation sites fluctuated
between 60o/o and 90o/o during summer and reached 95o/o over winter. Survival at the middle
elevation site was lower, with this difference fluctuating between 25 and 40o/o during
summer. The three highest ranking plant species in the diet of weta from all three altitudes
have an unusually high lipid content, indicating that high lipid species may be an important
diet item for H. maori. However, there was no difference in the diet preferences of adult weta
at high, intermediate and low elevations, suggesting that food quality does not have a strong
influence on body size. The results from the common-garden laboratory experiment revealed
a significant altitudinal difference in growth rate, with high altitude weta having a faster
growth rate, and low altitude weta a slower growth rate, under both warm and cool
temperature treatments. If fast growth is an unavoidable consequence of high environmental temperatures, then slow growth will be selected for in low altitude weta if it increases the
fitness of some other trait, such as larger adult body size and increased fecundity. At high
altitudes, delayed maturity due to slow growth and cool temperatures increases the risk of
1nortality prior becoming an adult, and selecting for fast growth at high altitudes may
represent a trade off between increased fecundity and minimising the risk of juvenile
1nortality. The results of this study are discussed in relation to the impact of global warming
on alpine weta populations.