Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

FNZ 39 - Molytini (Insecta: Coleoptera: Curculionidae: Molytinae) - Conservation Status and Value

Craw, RC 1999. Molytini (Insecta: Coleoptera: Curculionidae: Molytinae). Fauna of New Zealand 39, 68 pages.
( ISSN 0111-5383 (print), ; no. 39. ISBN 0-478-09325-X (print), ). Published 4 Feb 1999

Conservation Status and Value

Large weevil species are generally considered in New Zealand conservation biology (e.g., Ramsay et al. 1988, Thomas 1996) to be at threat from introduced rodent predators. There is some anecdotal and empirical evidence supporting this supposition. Bull (1967) provided evidence that mice prey upon L. huttoni adults, and Kuschel (1971) attributed the absence of H. stilbocarpae on Big South Cape Island - where it was once present - to predation by rats. While rodents undoubtedly prey on these weevils, other factors such as habitat degradation and destruction due to agricultural practices, reduction in the size and extent of host plant populations through browsing by stock and wild goats (Meads 1990), and even removal of the entire habitat through quarrying (which happened to a viable population of L. huttoni at Owhiro Bay, south Wellington coast) pose just as great a threat as rodents to populations of these endangered flightless species. Rodents may also compete for host plants with these weevils, as Roberts (1895) has noted that introduced rats feed on the roots of Aciphylla.

In 1980 H. spinipennis, H. stilbocarpae, H. tuberculatus, and L. huttoni were added to the protected fauna list in the Seventh Schedule of the Wildlife Amendment Act 1980. Being taxonomically and ecologically diverse, individually habitat specific, phytophagous on specific host genera, and easily identified, these relatively large weevils would seem to be an ideal biological indicator group for the purposes of conservation and environmental assessment.

There is increasing interest in utilising phylogenetic hypotheses as measures of biodiversity in prioritising, ranking, and targeting species for 'conservation value' (e.g., Williams et al. 1991, 1993, Faith 1994, Humphries et al. 1995). Application of the taxonomic root weighting method (Williams et al. 1991) to the phylogenetic tree provides a means of assigning quantitative values for each species or species-group in that tree (Table 3).

Fortuitously, root weighting analysis indicates that, given the present situation and current legislation, protection of these endangered, rare, and vulnerable species covers 39.68% of total taxonomic diversity of New Zealand Molytini. According to this method the next taxon that should be added to the protected fauna list is either H. pittospori or L. glacialis. Addition of either one or other of these taxa would bring protected taxonomic diversity coverage up to 48.49% of total taxonomic diversity for this group. Nearly 50% of total taxonomic diversity would therefore be protected by listing only 25% of species in this clade. Since three Hadramphus species are already on the list, it would be more desirable to conserve L. glacialis to maximise the number of clades protected. Root weight values can also be combined with information from geographic distribution, to identify and rank 'critical areas' for biodiversity preservation, by summing the percentage taxonomic diversity values for a selection of areas where two or more species occur (Table 4).

In setting conservation priorities taxonomic root weighting gives much higher weights to earlier diverging, basally branching taxa (Humphries et al. 1995). While there are sound reasons for assigning high conservation priority to taxa basal within their lineages (Stiassny & de Pinna 1994), weighting methods that emphasise their species-rich sister clades also deserve consideration. An alternative approach is to attempt to conserve taxa that may be able to support further evolution. This is the methodology advocated by Erwin (1991), who suggests that members of rapidly evolving clades or 'evolutionary fronts' have more potential to lead to future diversity than species-poor lineages. As basal lineages of New Zealand Molytini are species poor and have already received a much higher weighting in conservation prioritisation and legal protection, consideration should be given to protecting some of the more speciose high-altitude Lyperobius clades. Rather than adding a further early diverging species to the protected list, members of the montane to subalpine L. coxalis, L. hudsoni,or L. spedenii species-groups could be granted consideration as the next conservation priority. Placing priority on one or more of these speciose clades would also maximise the diversity of habitats occupied by the conserved species. At present most conservation effort and legislation are focused on basal lineages inhabiting coastal, lowland, and insular habitats.

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