In the year of the salamander people might wonder why we should care about plummeting salamander numbers, as this question is posed a lot when it comes to species conservation. Well for starters, just like you and me every creature has an intrinsic value, is valuable merely because it exists. It does not have to earn its right to exist, because who determines the criteria for earning this right and more importantly who could ever be the judge of that? The Buddha urged his followers to love every living being, be it human or animal (or otherwise). And this means to me that if we are responsible for declining numbers of animals we should try to help them and do our utmost best to keep them among us. But I understand that in our modern worldview valuing a creature just for its existence will not generate much applause (notice for instance how the unemployed struggle to find any meaning in their life, as they feel useless). But there are some very strong arguments to put forth that show how every species is indispensable to human well-being; alas we hardly take notice of these arguments. We fail to fully appreciate the importance of every part of an ecosystem and we fail to appreciate the vital role these creatures and ecosystems as a whole play in our everyday life. That’s why I want to discuss now a recently published research article that has demonstrated how woodland salamanders in temperate forests enhance carbon storage in the soil. A vital service to humankind as we have failed, up till now, to curb our greenhouse gas emissions sufficiently.
Before discussing the research into more depth, let’s focus first on the concept of ecosystem services, of which this carbon storage in the soil is a good example. Ecosystem services are defined as ‘the benefits that flow from nature to humankind’. This aligns pretty well with our modern worldview; even so much that it might seem to lean too much on the idea that nature has to be useful to humans to have any real value. However I find it to be a very useful concept, because it gives strong reasons for conservation and at the same time enables us to understand better the intricate relationships in the world around us. Those services have been recognized by scientists in the 19th century, but the concept of ecosystem services became really popular in the nineties and during the most recent years has received more and more attention from the scientific community. Good examples of these services are pollination of crops by insects, water purification, nutrient cycling and carbon storage, but also things like recreational opportunities, aesthetic and cultural value and provision of food. In short, the list is almost endless, of course because we rely entirely on our natural world for our well-being.
An important realm of research has been to determine how the provision of ecosystem services is influenced by biodiversity. Does the presence of more species mean that more ecosystem services are delivered to us or do some species have a much greater share in them than others? Although this is work in progress and no conclusive answers can be given, it seems that some species do contribute much more than others and therefore other species can be considered ‘redundant’. At the same time these ‘redundant’ species can step in and take over whenever an ‘important’ species is declining. This redundancy makes for a more resilient ecosystem that can therefore deliver a more stable flow of ecosystem services. For more in depth information about ecosystem services I refer you to the Millennium Ecosystem Assessment, a very ambitious project that set out to determine the state of our ecosystems and the services they provide. Just like biodiversity the flows of ecosystem services are decreasing and especially the people in developing countries are paying the price for this.
Amphibians provide us with ecosystem services as well. They range from direct services like food and medicines to indirect services like pollination, pest control and disease regulation. I will elaborate on these different services a bit. Frog legs are still considered to be a delicacy in the French cuisine and the Chinese giant salamander is highly prized for its meat in China. We could argue however that amphibians do not constitute the main ingredient in most people’s diet; more vital to the well-being of humanity as a whole is the potential for medicines that amphibians harbor: for example the toxic skin secretions of Atelopus zeteki show promising results in the treatment of cancer and the extinct gastric-brooding frog held the key to developing medicines against stomach ulcers. The indirect services have to do with the ecological role that amphibians fulfill: they mostly prey on invertebrates that, when they become too abundant, can have severely negative effects on crop yields and can lead to the rapid spread of diseases. For instance fly and dragonfly larvae can be host to human pathogens and are being kept in check by amphibians; just like caterpillars and leaf-cutting ants can decimate soybean yields and fortunately are on the menu of different toads. A world without amphibians therefore would give insects the freedom to proliferate exponentially at the expense of human well-being. Amphibians take part in pollination of different plant species as well: for instance maracuya and guava trees rely partly on pollination by several amphibian species.
What I haven’t mentioned is that amphibians like salamanders also positively can impact the uptake of carbon in the soil, thereby helping to abate climate change. A research recently conducted has shown this indirect service to occur in temperate forests in the United States. The authors set out to investigate the effects that woodland salamanders have in these forests on the density of invertebrates living on the forest floor that play an important role in recycling of leaf litter. As mentioned before, woodland salamanders are among the most numerous vertebrates in temperate forests, occurring in densities of 2950-18000 individuals per hectare. Although the term apex predator evokes images of white sharks hunting ferociously in the sea and lions dominating the plains of Africa, within this ecosystem salamanders can be considered top predators as well. And these apex predators are very important in keeping the ecosystem healthy. In the experiment in a conifer/hardwood forest in Northern California, adult male salamanders were put into a 1.5 m2 enclosure during two seasons in consecutive years. The enclosures were constructed in such a way that migration of prey invertebrates was made possible without salamanders being able to escape. During the experiment the scientists kept track of invertebrate densities and species composition and the amount of leaf litter present in the enclosure.
The results indicate the next findings: these salamanders have a profound impact on invertebrate densities and can influence species composition as well. These effects were tempered by an increase in moisture: in wetter seasons invertebrate densities soar and predation by salamanders has little impact. However, they still target specific species and thereby influence the species composition. The most important finding, in the light of climate change, was that the amount of leaf litter that is processed by invertebrates, making it biologically available again, decreases in the presence of woodland salamanders. This means that more leaf litter remains on the forest floor and will eventually end up in the soil through humification. In this way carbon is fixed in the soil and not released back into the atmosphere. Considering the soil is the most important terrestrial sink for carbon, salamanders can indeed play an important role in fixing carbon and abating CO2-emissions. A rough estimate by the researchers suggests that 200 kg of carbon per hectare extra is fixed into the soil due to the predatory activity by salamanders. This service is often overlooked, but occurs throughout ecosystems as also frogs and lizards can do the same in tropical forests. Sadly enough, these creatures that provide such a vital ecosystem service, are affected by climate change as well. Preserving them means we help ourselves and let’s hope this message reaches the general public as well!