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Two taxa, Tormus nitidulus Broun and Pyncnomerus latitans Sharp are treated as outliers in this study and are not included in the reconstructions shown in Figs. 6.6a-c, 6.7a-c or 6.8a-c. The reasons for excluding these taxa have already been discussed in Chapter 4 and are not repeated here.

Split climate envelopes

Some samples within the final palaeoclimatic reconstructions (Figs. 6.6a-c, 6.7a-c &

6.8a-c) contain multiple possible climate reconstructions for the same set of data (e.g.

samples H3, H7 and H11 in Fig. 6.6a-b; samples H3, H6, H7 and H11 in Fig. 6.7a-b;

samples H9 and H11 in Fig. 6.8b-c). While these “split climate envelopes” could result from taxa with poorly delimited climate ranges the MLE envelopes are consistent with the known habitats of the beetles causing the splits. Sample H3 (Fig. 6.6a, Fig. 6.7a) is an example. Most of the taxa in this sample are associated with forest environments (Table 6.1) but Aleochara hammondi Klimaszewski is a tussock grassland type and is now confined to alpine settings (Klimaszewski & Crosby, 1997).

While the present day vegetation of the West Coast comprises a sequence of floristic zones from shrubby forest at the coast, through lowland podocarp-beech forest on the coastal terraces, montane beech forest on the mountain slopes and subalpine grassland above the tree line (McEwen, 1987; Wardle, 1991), this was not the case during the period covered by this record. The palaeoenvironmental reconstruction for this site illustrates that the vegetation of the Westport region during the time period covered in this study comprised a mosaic of closed-canopy lowland forest mixed with shrubs and alpine grassland. This mosaic environment, comprising flora from a number of modern environments, would enable beetle taxa from different habitat types (e.g. forest and tussock grassland) to co-exist in the same general area so long as other factors (such as climate) were not limiting. This intermingling of taxa that in a modern day setting appear climatically segregated emphasises the need to understand the ecology of beetles when attempting to interpret estimates of glacial period palaeoclimate from fossil beetle assemblages.

Beetles and climatic limitations

Beetles are poikilothermic and low temperatures can have a multitude of effects. These include slowing of metabolism (Gillot, 1991), an inability to gain enough heat energy from the environment to complete development (Hodkinson, 2005), cell dehydration (due to the removal of water through freezing) (Franks et al., 1990) and the lethal crystallisation of water in insect tissues (Sinclair et al., 2003a). Beetles are therefore actively limited by cold temperatures and the low-end estimate of the MLE minimum winter temperature reconstructions may represent hard climatic limits below which a beetle taxon is less likely to survive. This suggests that it is a reliable estimate of the lower limit of minimum winter temperatures. On the other hand, the upper limit of the winter temperature reconstruction is based on ecological preferences as there is no physiological reason why warmer than average winter minima will limit the survival of taxa (so long as the temperature remains below the taxon’s upper thermal limit).

While the upper limit of the winter temperature reconstructions is unlikely to be physiologically limiting it does indicate an ecological preference and still provides useful data. As variation in the upper limit of a winter temperature reconstruction relates to the presence or absence of beetles with preferences for cooler conditions changes in the upper limit reflects variation in the temperature. For example, if taxa that prefer cold conditions disappear from a record then the upper limit of the reconstructed climate range will increase implying an amelioration of winter temperatures.

Like the beetle-based winter temperature reconstructions, the upper boundary of precipitation estimates are unlikely to be limiting as it is water stress, caused by loss of

moisture from the beetle to the environment, that is the physio-chemical limitation on beetle survival (Edney, 1977; Hadley, 1994). The only time a high level of precipitation is likely to be limiting is when it is high enough to result in flooding and drowning of beetles. As this is not a function of total rainfall, but rather individual rainfall events and the hydrology of the site, high-end estimates of precipitation are unlikely to be ecologically limiting. It is therefore the minimum estimate of the upper (pink) envelope (Fig. 6.8b-c) that acts as the robust limitation on precipitation reconstructions. The exceptions to this are reconstructed envelopes based around high alpine taxa which occur above the treeline (e.g. Aleochara hammondi and Adrastia nelsoni). Limiting factors in high alpine areas include a variety of factors including high UV radiation, low minimum temperatures and moisture stress relating to drought (Hodkinson, 2005). While sporadic droughts may indeed be limiting for these taxa we consider it unlikely that annual rainfall in excess of 4,000mm is required for A. hammondi to survive. It is more likely that winter minimum temperature is the limiting factor for these high-altitude taxa and consequently the upper estimates for samples constrained by alpine taxa alone (samples H11, H7, H6, H3 and H2) have been ignored. The elimination of A. hammondi from the precipitation reconstructions damps down a pattern which is visible with or without this taxon. As the upper estimated limit of the precipitation reconstructions reflects the ecological preference of the taxa in the assemblage variation in the upper limits is still representative of variation in the amount of precipitation.

While beetles do appear to distribute themselves in relation to mean summer temperature (Chapter 3) it is unlikely to be a direct physiological control on their distribution as