The Amazon Rainforest showcases tremendously high genetic diversity and species richness per unit area (Phillips et al., 1994), one of the highest worldwide. It's a global biodiversity hot-spot and is extremely important to preserve! Although the research into this may not be what you expect. The Amazon is actually classified as a zone of low vulnerability as far as biodiversity conservation efforts go. Despite this, it's also a zone of high irreplaceability due to its sheer amount of biodiversity being so ecologically important (Brooks et al., 2006). It's important to consider this when discussing the Amazon Rainforest, even though it may seem contrary to the narrative I've laid out so far. It's not quite as doom and gloom as it seems, but that doesn't mean there isn't a problem!
A recent study explored the effect of building dams for hydropower in the Amazon, Congo, and Mekong river basins and found a worrying correlation between fish diversity and the location of dams (Winemiller et al., 2016) (Figure 1). These basins contain approximately one-third of the world's freshwater fish species (2320 in the Amazon, 1488 of which are endemic), all of which are at risk of population decline. Figure 1 shows just how impactful dam constructions are on fish diversity, and the density of proposed dams in already-impacted areas is concerning. One bit of hope that Winemiller et al. point to, however, is that actual fish diversity is underestimated since multiple new fish species are discovered annually.
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| Figure 1: The distribution of existing and planned dams in the Amazon river basin and the species richness distribution. Areas of high dam density appear to coincide with areas of lower species richness. (Source: Winemiller et al., 2016) |
In terrestrial fauna, models suggest that significant land-use change in the central Amazon results in biodiversity loss by causing forest fragmentation (Dale et al., 1994). As forest is cleared for anthropogenic use, parts of the forest become isolated from each other, so the total available habitat area for species becomes smaller, particularly for relatively immobile species incapable of crossing these gaps. Ultimately, with a smaller living space, biodiversity rates decrease. Any guesses at what organisms have little to no gap-crossing ability whatsoever? That's right, plants!
The floral side of Amazonian biodiversity is a bit less clear though. According to Hopkins (2007), our knowledge of floral biodiversity in the Amazon is limited by a lack of data, since very few regions of the rainforest are well-documented. This suggests that what knowledge we have is very biased to these few regions and we have little understanding of how floral diversity is distributed across the Amazon. Hopkins' study actually indicated that four major regions of the Amazon basin are poorly understood and likely contain a significant number of plant species. This is particularly problematic given the fragmented nature of the Amazon under current forestry regimes and their propensity to house endemic species as a result (Dale et al., 1994). It's entirely possible that the biases towards certain regions and forest fragmentation mean that our estimates of total floral biodiversity are under or overestimated. Bloody forest clearing. We're compounding our own problems!
Land use change isn't the only thing likely to affect Amazon biodiversity in the future though. Climate Change is a pesky old thing! Increasing temperatures under climate changes and increased frequency of extreme weather events (that can often lead to fires) are predicted to cause habitat destruction and fragmentation, and subsequent species extinctions (Brodie et al., 2012). Though this is acknowledged to be under circumstances in which such changes result in organisms needing to change their habitat distributions in order to avoid rising temperatures under climate change. Unfortunately, Brodie et al. suggest that these extinctions would be the most severe in low lying tropical rainforest drainages, where organisms try to reach higher elevations where temperatures are cooler. Yep, that includes the Amazon.
Remember the anthropogenic fires I talked about in a previous post? Remember how our forest clearing is increasing the possibility of these? Well, yeah, we're ruining things again. If Amazonian ecosystems are unable to adapt or cope with increased fire frequency, then habitat destruction is going to increase as a result, and put a greater number of species at risk of extinction. Worst case scenario; some models have predicted that this deadly combination of climate change and land use change (I told you everything was interlinked!) will cause large scale drying in the Amazon and large enough increases in fire frequency to reach a tipping point in some parts of the Amazon by 2030, causing a shift to drier, savanna-like ecosystems (Nepstad et al., 2008). Figure 2 depicts exactly where this has been predicted.
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| Figure 2: The extent of predicted dry forest covering the Amazon by 2030 as a result of large scale drying under climate change. (Source: Nepstad et al., 2008) |
The profound negative impacts this would have on indigenous peoples is bad enough (Finner et al., 2008), let alone the decrease in biodiversity this would lead to. Tropical Savannah and dry ecosystems typically exhibit lower rates of biodiversity than tropical rainforests (WWF, 2006). Although Savannah ecosystems are still quite diverse, they do not make suitable habitats for most rainforest species that exist within relatively narrow climate envelopes. One thing to note though, is that this shift is projected by a model. It's not a given, so interpret this with a critical lens.
There's a lot science is unsure of or can't decide on, such as Amazonian floral biodiversity, or just how vulnerable the Amazon actually is. What we are quite confident about, however, is that this biodiversity hot spot isn't doing as well as it could be. A lot of species in the Amazon are at risk currently; we're just not sure how much risk. While significant Amazonian extinction may not occur within our lifetimes, we must be careful not to breach a tipping point in the Amazon to cause mass extinction in the future. We certainly don't want the Amazon to follow the same trend as the global genetic diversity planetary boundary.
And on that depressing note, I'm out. See you next time!
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