A 20-year Record of Alpine Grasshopper Abundance, with Interpretations for Climate Change

A 20-year capture-recapture study of alpine grasshoppers spanned three distinct sequences of abundance, featuring in turn dis-equilibrium, equilibrium and secondary cyclic equilibrium. This succession of population patterns in the most abundant species, Paprides nitidus, retained high stability between generations. It arose via superimposed life-cycle pathways and adaptive responses between grasshopper phenologies and their environmental constraints. The responses were identified by correlation coefficient analysis across extensive matrices (11 500+ correlations) of environmental records x time-lagged grasshopper estimators. An estimator of resident population members performed better than total population estimators. The observed retention of population stability despite shifts in the patterns of abundance implies some predictability, and potential effects of climate change (increased temperature, rainfall and raindays) are examined in a context of global warming. It is concluded that flora and fauna could eventually become depleted in alpine regions due to the displacement of grasshopper populations to vegetation-scree margins where physical weathering and vegetation instability are often pronounced. The highly flexible P. nitidus life cycle emphasises a high level of variation in egg phenology, whereby alternative overwintering pathways (quiescence, diapause, extended diapause) lead to variable life-cycle durations. The schematic cycle accommodates two quite different species, Sigaus australis and Brachaspis nivalis, and is probably applicable to New Zealand's alpine Orthoptera in general. Population mortality sequences are identified throughout the cycle, and the 20-year census history suggests that a classic predator-prey response may arise between a native skink species (Reptilia) and grasshoppers.