Tuesday, 9 July 2013

What is the influence of climate change on Tanzanian protected areas?

Pangani Longclaw Macronyx aurantiigula is perhaps the best example
of a species extending west, having colonised Serengeti recently.
It's been a long time since I posted anything here - sorry! I have another common birds post in progress, but just keep failing to finish it off. In the mean time I thought I'd talk about one of my own papers that came out a few weeks ago that explores how Tanzanian bird distributions are changing (sorry, it's pay to view, but if you want a copy email me and I'll send it!). This analysis is a fairly major result of my collaboration with the Tanzania Bird Atlas and represents the combined efforts of a very large number of people, volunteers and professionals, who contribute invaluable data to Neil and Liz Baker - I know some of you read this, so firstly, thank you, and secondly, I hope you appreciate seeing how we can use these records to do interesting and (I hope!) useful research.


So, what did we do? In brief, we took all the records of some 139 savannah bird species and lumped them into two different time periods - 1960-1989 (before most of the current climate changes had generated much change) and since 2000. We then built statistical models that accounted for changing patterns in observer effort, to identify places where each species had colonised or vanished (local extinction) between the two time periods. As well as telling us where these birds occur, this also allowed us to identify the climate that was preferred by each species during the initial time period. We then analysed these changes to look for consistent patterns in the places where colonisations or local extinctions had occurred, looking particularly at changes in climate suitability for each species, trends in land degradation, and protected area status in each place.

From Beale et al 2013 The overall pattern of changes in distribution among 139 Tanzanian savannah bird species. (a) Continuous presence, (b) colonisations, (c) local extinctions, (d) continuous absence. Square size indicates average transition probability across all 139 bird species, with colonisations and extinctions magnified 10 times relative to continuous presence and continuous absence.
We discovered some very strong patterns as many savannah birds are changing their distributions at the moment. There's a general movement of dry country species to the north and west (see map of overall changes). These changes parallel many observations of range change in temperate regions where climate change is the likely cause, as birds respond to changing temperatures by moving north. In Tanzania we found that the overall pattern of colonisations was associated with climate change - dry country birds moving into areas with newly longer dry seasons - but that local extinctions are driven primarily by land degradation, not (yet) by climate change. Over and above this broad pattern is a strong association with protected areas: as birds colonise new areas where the climate is improving for them, so too do they preferentially occupy protected areas. Equally, because protected areas successfully buffer the impact of land degradation, local extinctions are less likely to have occurred in protected areas. The obvious consequence is that the value of current protected areas is growing. This is particularly important, as it has been suggested that climate-induced distribution shifts might move species from protected areas, leaving the current protected area network in the wrong place. Our results suggests that, at least at present, keeping current protected areas safe is an effective response to climate change, which is doubly surprising as the protected areas were originally identified to protect mammals and no real consideration was given to birds or anything else

Another classic dry bush species, the Scarlet-chested Sunbird
is not yet shoing major movements.
So, that's what I think is interesting about the work. There's still a lot of work to go: I still don't really know the details of why many of these species are changing ranges: they are clearly responding to changing rainfall patterns, but the effect that causes this is not direct, it must be mediated through some very subtle change in the environment. My guess is that rainfall patterns might be altering grass quality (without altering the habitat: these areas are still bush/grass savannas), which might in turn influence a range of invertebrates that the birds follow, but there are lots of questions still to answer here! Keep sending your records in...

Main Reference:
 ResearchBlogging.org Colin M. Beale,, Neil E. Baker,, Mark J. Brewer,, & Jack J. Lennon (2013). Protected area networks and savannah bird biodiversity in the face of climate change and land degradation Ecology Letters DOI: 10.1111/ele.12139

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