The vulnerability of flightless ground beetles (Carabidae) to climate change in the Australian tropical rainforest

Staunton, Kyran Michael (2013) The vulnerability of flightless ground beetles (Carabidae) to climate change in the Australian tropical rainforest. PhD thesis, James Cook University.

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Abstract

As climate change continues to threaten global biodiversity, knowledge of the fundamental processes influencing species' distributions is vital to determining their vulnerability. This thesis investigated the distributions of a diverse insect group, flightless ground beetles (Carabidae), in the tropical rainforests of Australia. Influences from abiotic (such as climatic) and biotic (such as lowland ant richness) factors were analysed in relation to this group and projections of future distributions, abundance and richness patterns determined under multiple climate change scenarios. This thesis is the most detailed ecological investigation into any flightless insect taxa as well as ants to date within the Australian World Heritage Wet tropics Area (hereinafter the "Wet Tropics").

Flightless ground beetle distributions were determined throughout the Wet Tropics using both spatial distribution modelling and standardised sampling across elevational gradients. The sampling of flightless ground beetles and ants occurred primarily using 210 pitfall traps across elevational transects from 5 separate mountain ranges throughout the Wet Tropics, between 2008 and 2010. Location data from this sampling was combined with data from the Queensland Museum to create spatial distribution models. Additionally, future vulnerability of flightless ground beetles was assessed in a climate change context, under multiple emissions scenarios using distribution modelling techniques. Changes in community patterns were investigated and linked to environmental factors across spatial and temporal frameworks. Finally, relationships between flightless ground beetle and ant (a suggested competitor) richness and abundance changes were investigated.

Flightless ground beetles predominantly inhabit upland areas characterised by stable, cool and wet environmental conditions. These beetles generally displayed highly restricted distributions, and therefore were most species-rich, in mountain-top habitats. Of the climatic variables modelled to best explain this taxa's species richness, maximum temperature of the warmest period contributed the most. These distribution and richness patterns supported the time-stability hypothesis (whereby, more climatically stable habitats contain greater diversity) as this group's primary habitat, upland rainforest, is considered to be the most stable habitat within the region.

In future, flightless ground beetles throughout the Wet Tropics are projected to substantially reduce their current range sizes, population sizes and species richness under all emission scenarios. These projections were determined using multiple emissions scenarios, derived from the Intergovernmental Panel on Climate Change's Special Report on Emissions Scenarios. Future ranges are projected to contract as distributions shift upwards and subsequently species richness is expected to decline. However, the greatest impact of climate change on flightless ground beetles was indicated to be extreme reductions in abundance, with 88% of species modelled predicted to decline in population size by over 80%, for the most severe emission scenario by the year 2080. Of this taxa, species currently restricted to more marginal mountain ranges (those characterised as drier and with lower summits) are projected to be the most vulnerable to climate change impacts. Seasonal investigations also indicate that, as flightless ground beetles are inactive during dry seasons, projected increases in dry season length will negatively affect this taxa. These results suggest that flightless ground beetles are among the most vulnerable taxa to climate change impacts so far investigated in the Wet Tropics. Such findings have dramatic implications for all other flightless insect taxa and, therefore, the future biodiversity of this region.

Flightless ground beetle communities are highly distinct between subregions throughout the Wet Tropics. Such high levels of dissimilarity of flightless ground beetle assemblages between subregional blocks were attributed to factors including: low dispersal between subregions, a high level of in situ evolution, extinction filtering events and current climatic conditions. Regarding current climatic factors, differences between subregional assemblages were linked to changes of: temperature seasonality, maximum temperature, precipitation seasonality, wet season rainfall and minimum temperatures. Furthermore, species richness and abundance of flightless ground beetles significantly increased with elevation throughout the Wet Tropics and therefore species generally inhabit cooler, wetter locations.

Richness and abundance changes of the flightless ground beetle community were not only strongly linked spatial variance in climatic factors, but also seasonal changes. Beetle activity increased between November and February (during the wet season) and correlated positively with changes in both temperature and precipitation. Across the Wet Tropics landscape, the precipitation seasonality of a site negatively correlated with both richness and abundance of flightless ground beetles. This pattern adds further support to influences from the time-stability hypothesis. Seasonal changes in environmental factors were strongly linked to changes in activity, richness and abundance of flightless ground beetles.

The literature suggests that flightless ground beetles display restricted mountain-top ranges due to either intolerance of lowland climatic factors or overwhelming competition from lowland ant species. Such suggestions were assessed by analysing co-located ant and flightless ground beetle data across multiple elevational transects.

Like flightless ground beetles, the ant community is strongly linked to climatic conditions. However, unlike flightless ground beetles, ants display highly similar assemblages within similar climates throughout the Wet Tropics, regardless of geographical distance, elevation, or potential barriers to dispersal. Consequently, the lowland ant community, which is highly species-rich, is expected to be able to easily migrate up mountains, as climatic conditions become favourable due to climate change. Such migrations would result in much greater species richness in future highland ant assemblages.

Negative correlations were revealed between flightless ground beetles and ant richness and abundance across the elevational gradients. However, despite such correlations, variances in both beetle abundance and richness were best-explained by climatic factors when considered in a combined statistical model. Subsequently, flightless ground beetles are considered to respond primarily to changes in climate, rather than ant richness or abundance, across the elevational gradients. Therefore, any future reductions in flightless ground beetles are expected to predominantly occur due to changes in climatic conditions rather than possible climate-induced changes in ant richness.

Flightless ground beetles are highly vulnerable to projected climate change impacts. This high sensitivity implies that similar flightless mountain-top taxa, the vast majority of which remain unstudied, may be similarly threatened by climate change. Future research must address this lack of understanding if climate change impacts on mountain-top ecosystems are to be comprehensively understood.

Item ID: 40690
Item Type: Thesis (PhD)
Keywords: ants; Carabidae; climate change; climate; ecology; flightless beetles; global warming; ground beetles; habitat management; Queensland; rain forest; rainforest ecology; rainforest; tropical climate; tropical rainforests; Wet Tropics of Queensland; Wet Tropics World Heritage Area; Wet Tropics
Additional Information:

Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2: Staunton, Kyran M., Robson, Simon K.A., Burwell, Chris J., Reside, April E., and Williams, Stephen E. (2014) Projected distributions and diversity of flightless ground beetles within the Australian Wet Tropics and their environmental correlates. PLoS ONE, 9 (2). pp. 1-16.

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Date Deposited: 01 Oct 2015 03:52
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050101 Ecological Impacts of Climate Change @ 34%
05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050211 Wildlife and Habitat Management @ 33%
05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050206 Environmental Monitoring @ 33%
SEO Codes: 96 ENVIRONMENT > 9603 Climate and Climate Change > 960305 Ecosystem Adaptation to Climate Change @ 34%
97 EXPANDING KNOWLEDGE > 970105 Expanding Knowledge in the Environmental Sciences @ 33%
96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960806 Forest and Woodlands Flora, Fauna and Biodiversity @ 33%
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