It’s been a good few weeks with many of our papers coming out online early – for example, I highlighted one last week on ecosystem function breakdown from global warming.
Although this has been out for a few weeks, our new paper lead by PhD candidate Xingli Giam (formerly of National University of Singapore, recently completed Australian Endeavour Scholar, now at Princeton University and all-round up-and-coming research star), and with contributions from Hugh “Vascular” Tan and Navjot Sodhi of National University of Singapore and me, is entitled Future habitat loss and the conservation of plant biodiversity (just published online in Biological Conservation).
This one is a bit of a complicated one, so let me walk you through it.
Plants not only represent a huge component of global biodiversity (~320 000 species), they represent the ‘habitats’ in which animals live and provide the major source of nutrients to food webs. They also provide most of our food and other materials essential for human existence. Basically we’d be screwed without them.
Because so many of the world’s biomes are severely threatened now because of massive habitat loss, degradation, over-exploitation, invasive species, extinction synergies and climate change, we need to maximise our efficiency in protecting what’s left. While global prioritisation schemes have a fruitful scientific history since Myers & colleagues’ classic paper (see Biodiversity Hotspots), there are a number of problems that plague the concept and its implementation.
Apart from the most serious problem of the difficulty of convincing governments and the people who elect them that we are losing way too much biodiversity for our own good, there are some other issues with the ‘Hotspot‘ concept. First, there are many, many different ways to prioritise areas for conservation, and most of them give rather different prioritisations (see Brooks and colleagues’ classic paper on the subject). Second, none of the global prioritisation schemes explicitly consider future habitat loss patterns and the rising effects of climate change (although a few studies have predicted future plant extinction patterns based on land-use and climate change projections (Thuiller et al. 2005; Van Vuuren et al. 2006).
Because we expect species already threatened to be more vulnerable to extinction in the future than non-threatened species, future projections of conservation need realistic estimates of threatened species distributions in addition to the predicted magnitude and extent of future habitat loss.
We therefore assessed the exposure of threatened plant biodiversity to land-use and climate change-driven habitat loss up to year 2050 by testing the hypothesis that countries with higher threatened plant species richness are likely to suffer from greater relative habitat loss given recent historical trends in loss.
To do this, we used the number of endemic plant species per country as a proxy for the number of threatened species and then used the residuals in the power-law endemic species-country area relationship as an index of endangerment.
The potential extent of future habitat loss owing to land-use and climate changes in each country was derived from the Millennium Ecosystem Assessment. We then determined which countries are most prone to plant biodiversity loss by by relating the current degree of plant species endangerment with the amount of projected total habitat loss.
Finally, because poorer countries have limited financial means for conservation projects such as the enforcement and monitoring of protected areas, we hypothesised that these might be at greater risk from habitat loss, direct harvesting, and encroachment of invasive alien species. Poor governance can result in the degradation of biodiversity owing to ineffective management and corruption, so we also identified countries of high conservation need by considering their wealth and quality of governance with the future plant species endangerment ranks.
Whew! Quite a list!
While I won’t focus to heavily on the mathematical side of things, I was particularly proud of our novel approach to fitting species-area relationships to estimate the total number of threatened species per country. We used probably one of the most parsimonious, model-averaged, biome-specific power-law approaches with the appropriate distributions developed to date, and I personally think our approach represents a major leap forward in species-area relationship fitting (with inspiration from Guilhamon and colleagues). But that’s another story.
Given the number of aims, there were quite a few results. I’ll just summarise the salient points:
- endemic species richness data were available for 196 countries
- 143 countries overlap with the network of Biodiversity Hotspots and they contain 206905 endemic plant species
- the remaining 53 non-Hotspot countries contain only 7812 endemic species
- the highest relative index of plant species endangerment was in tropical America, tropical Asia and southern Africa
- the five countries with the highest endangerment are: Papua New Guinea, New Caledonia, South Africa, Indonesia, Colombia
- in Hotspot countries, the index of current plant species endangerment was positively correlated with future climate change-driven and climate change-driven habitat loss
- countries with the highest future plant species endangerment are concentrated around the equator
- the following countries were ranked in the category of greatest conservation need based on economic condition: Democratic Republic of Congo, Ethiopia, Kenya, Madagascar, Nepal, Tanzania, Tajikistan
- the following countries were classed in the category of greatest conservation need based on quality of governance: Angola, Cuba, Democratic Republic of Congo, Ethiopia, Laos, Myanmar, Nepal, Tajikistan, Venezuela
- there was a high overlap between the countries prioritised based on economic condition and those prioritised based on quality of governance
I think the major take-home message is that we need to consider an array of factors when prioritising regions for conservation need. It’s not enough to count species, one must also account for the mathematical uncertainty of region-specific endemism patterns, future habitat loss, climate change, and a country’s wealth and governance quality. We’ve come a long way since Biodiversity Hotspots!
Giam, X., Bradshaw, C.J.A., Tan, H., & Sodhi, N.S. (2010). Future habitat loss and the conservation of plant biodiversity Biological Conservation DOI: 10.1016/j.biocon.2010.04.019