Merry Christmas from the "Santa Spider"

Merry Christmas to all my readers! I hope you're all enjoying a good festive break from work, university and life. Whilst I'm sure you all have better things to do today than read my blog, I thought I would bring some ecology in to your day if you're up to it! The spider below is colloquially known as the ladybird spider or 'Father Christmas' spider, which as you can probably guess, is due to the bright red, white and black markings found on the males. It's one of the UK's rarest and smallest spiders and suffered from habitat degradation throughout the 20th Century.

Eresus sandaliatus, apparently trying to sniff out a female with organs on his legs; Source.

The spider is somewhat of a conservation "Christmas miracle" and has been brought back from the brink of extirpation in the UK to a now thriving population. The spider went from an estimated 50 individuals remaining in Britain in 1993 to well over 600 in 2000. The spider makes its home in heathland, which is one of the UKs most threatened habitats, and over 90% of it has been lost to development and agriculture since 1800. In Dorset, there has been concerted conservation efforts to restore the spider populations as well as protect heathland habitats. At one site there were only 7 spiders left, but there are now thriving and have been released from this site into other areas, where they have successfully colonised. Workers from the RSPB used plastic water battles filled with moss and heather to create houses for the spiders where they could breed safely.

A cute and inspiring conservation story - I try not to be too pessimistic on this blog!

 Merry Christmas!

Tiny spider is tiny; Source.

Plastic water bottle houses, Source.

Look Deeper: Extinction Risks to Soil Biota

Earlier this week, we celebrated World Soil Day (4th Dec). One of the key themes in this years festivities was to highlight the need to increase research into soil ecology and underground ecosystems. In particular, to warn of the potential underground extinction risks that we have an very limited understanding of. A new collection of papers has been published in Nature as part of World Soil Day to highlight these issues among other soil related discussions. So, in accordance, I will be bringing these issues to my blog to give us all an education about soil ecology, as despite the relative neglect compared other areas of ecology, the soil and its biota are fundamental components of all terrestrial ecosystems.

In order to form conservation approaches for underground ecosystems, we need a clearer understanding of the diversity and functionality of them. We know that soils provide vital ecosystem services, particularly for agriculture, so there is clear motive for conservation action - regardless of a lack of moral motive, as concern for things small and dirty tends to be less. The extent of biodiversity below ground is hugely unknown, partially due to the impracticalities of studying these organisms due to their size and inaccessible habitat.  As shown in the graph below, taken from one of the new papers, the vast majority of what lives in the soil is under 1mm in size. What the graphs also shows, however, is the extreme abundance of these organisms - over 1kg of bacteria per meter squared is an insane amount of individuals! Aside from our poor understanding of the diversity, other challenges for understanding potential extinction risks include the lack of suitable models, the complexity and density of microhabitats within the soil and uncertainty about temporal and spatial scales. I'm not going into these here, but they are all detailed here if you're interested!

Soil biota, shown by coloured crosses, are generally very small and very abundant ; Source. 

The most important extinction risk factors for soil organisms are not dissimilar to those faced by their terrestrial counterparts. Habitat loss, a concept we are all familiar with in relation to aboveground organisms, can cause equal disruption for soil ecosystems, for example through the fragmentation of the soil surface via urbanisation. This has been shown to link to declines in abundance of nematodes and other soil biota. Equally, climate change and global warming pose a threat just as they do to terrestrial and marine biomes. Extreme drought events can cause devastation of soil based habitats, for example. Climate change is also thought to have some more complex impacts on soils which can be equated to habitat loss, due to the degree to which the soils are changed. It has been shown that the increased atmospheric CO2 concentrations lead to a reduction of nematode diversity due to the loss of pore spaces in the soil which are required by the organisms. Soil habitats are also impacted by agricultural practices, such as tilling, irrigation and fertilization which impact both soil structure and composition. It is thought that these factors drive constant habitat loss for components of the subterranean community. Although it is difficult, as mentioned above, to know the extent of these impacts, we do know that many of the susceptible species, such as earthworms and mycorrhizas, are of major functional importance to their own ecosystems and ours. There are also potential risks from invasive species, but at a microbial level more than invertebrate, which have likely been spread as a result of travel and tourism. Many of the soil biota are highly specialized in their niche, which is commonly considered to make them more vulnerable to both invasions and extinctions.

So there are considerable risk factors stacked up against soil ecosystems, much as there are against the terrestrial. There has, unfortunately, been very little conservation action in comparison. Some studies have already documented local extinctions of earthworms and various fungi due to the factors discussed above. So perhaps we should start taking some action? This, if any, is a good time to start. 2015 is the International Year of Soils, as declared by the UN General Assembly, after-all. This declaration was made with the intent to raise awareness of the life-supporting functions of soils and to promote the importance of soils in achieving a number of the new 17 Sustainable Development Goals. I hope that you've learned something about the oft-neglected but important goings on beneath our feet, and that in future you might give them a thought in conservation discussions.

Happy World Soil Day! 

Invaders: A Response to Thomas and Palmer, 2015

Recently, a number of studies have highlighted that whilst we are suffering global biodiversity losses, local diversity is actually relatively stable, or in some cases increasing. This is due to a number of reasons, including increasing habitat heterogeneity and crucially the spread of strong generalist competitors. In the analysis conducted by Vellend et al., they found that whilst post disturbance was the only truly positive driver of vegetation change (as we would expect in accordance with the intermediate disturbance hypothesis, on which much of our conservation practice is based), invasion was the only factor which stood out as driving a decline in diversity.

Postdisturbance promotes diversity, whilst invasion seems to limit it. Source: Vellend et al., 2014

However, it is arguable that as the error margins cross zero, it is weak evidence for the derogatory effect of invasive species. Indeed, recent thinking has been that the impacts of invasions are not as significant as we have traditionally thought. Often primary production can be enhanced, and resident species do not always decline, overall less than half of the impacts were found to be statistically significant.  The study which this post focuses on, published earlier this year, focuses on the impact of invasive plant species in Great Britain. Across 479, sites, Thomas and Palmer found that diversity had actually increased, and that the negative impacts of invasive plants on British biodiversity had arguably been exaggerated.

Increased diversity of native species with non-natives, Source: Thomas and Palmer, 2015

Whilst their data is sound, I am inclined to disagree with their sentiment. Invasive species, particularly fauna but some flora as well, have had well documented negative impacts on native British ecosystems. Overall diversity can be a very crude measure of the health or success of an ecosystem, the composition is far more important - particularly if we are looking to safeguard our native biota. Yes, there may have been an increase in biodiversity, but is it the biodiversity we want? These patterns are not unexpected, invaders are particularly successful in frequently disturbed areas, which are also likely to be diverse areas due to the variety of niches to be exploited by fast growing colonisers. Indeed, if these areas are regularly disturbed, it will likely prevent competitive exclusion by the invaders and maintain diversity. This kind of ecosystem is far removed from our native climatic community of oak woodland. Perhaps I'm old fashioned, but I believe that our goals in conservation should be to maintain these native conditions as much as possible, rather than simply to maximise diversity.

Many examples of invaders, outside of the infamous grey squirrel, exist and are key issues in current British conservation.  The American Mink, which has all but wiped out our native Water Voles - diminishing populations by up to 94%. The signal crayfish, larger and more aggressive than to our native white clawed crayfish, are estimated to have reduced native numbers by 95%.  The aptly named Killer Shrimp spreads rapidly throughout freshwater ecosystems and has been shown to drastically decrease invertebrate and fish diversity, leading to simplification of food webs. Plants, as well, have had severe ecological consequences as invaders. Top of the most wanted list is Japanese Knotweed, which overruns fluvial ecosystems as well as much of our urban environment. There is even an invasive mouse which eats the chicks of a critically endangered Albatross species alive, documented in the British Overseas Territory Gough Island. The list goes on. The point is that there are many, many species which have and will have severe impacts on our native biota. The local lens must focus on what is actually happening in these local ecosystems, and we should be aware of what is happening to British wildlife before accepting sweeping generalizations that invaders have "no negative consequences for native diversity".

Purposefully evil looking pictures of invasive species

Habitat Fragmentation 1: The Need for Otter-ly Integrated Aquatic Systems

Habitat fragmentation is among the most blatant and well documented human abuses of our environment. The science behind it is not difficult to get your head around either - ever more isolated populations of both plants and animals are much less able to mingle with other populations and are therefore vulnerable to local extinctions (or extirpations). Simple metapopulation dynamics! There are many stories to tell about which species have suffered from this, and in a series of posts I plan to share a few of them, perhaps those which are not as immediately obvious.

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Eurasian Otters (Lutra lutra) are among Britain's cutest and most loved species. They suffered a very well documented and publicized decline throughout the latter half of the 20th Century, largely due to pesticide use, hunting and habitat loss. Thankfully, due to the ban of some of these pesticides and the implementation of conservation policies in the 80s and 90s, Otters have recovered from near extinction in Britain. As of 2011, Natural England announced that they were once again present in all English counties.  Hooray! But what do they have to say about habitat fragmentation?

Otters provide a perfect example to support the argument for landscape scale ecology, and conservation approaches that consider freshwater systems as an integrated whole.  Otters, among other creatures, utilise all components of the freshwater landscape: ponds and rivers, lakes and backwaters. In a study of the River Glaven in Norfolk, a well kept and highly interconnected river, droppings from the recovering otter population were found in a variety of freshwater habitats - showing distinct patterns throughout the year. In the summer, otters primarily fed on fluvial creatures such as the white clawed crayfish, but during the spring and winter, whilst the crayfish were hibernating and amphibians breeding, their diet consisted of >70% of still-water creatures. The study found evidence of otters in ponds over 1km away from the main river, which shows that even seemingly detached bodies of water are indeed integrated.

Map of otters in the River Glaven catchment, source: Sayer 2014

It is arguable that the otter populations in Norfolk would not have recovered as successfully if the habitat had been more fragmented. It is not only the otters themselves, relying on the ponds to feed them in winter, but the myriad of invertebrate and amphibian species that rely on the existence of a metapopulation to stabilise their demographics. Among those pond inhabitats with metapopulations are Great Crested Newts, Crucian Carp, dragonflies, mayflies, caddis flies... anything from a pond which ends in -fly really. All of these animals and the plants they feed on need a highly connected habitat to support their metapopulations and in turn they stabilise the ecosystem and support fluffier and more high profile predators like the otters. This is the case with any habitat, not just the ponds of Norfolk and as we considered the global picture of environmental change, we must not forget the little guys on the front lines that hold everything together. To those who are opposed to landscape scale ecology....

Upset Otter, source: QuickMeme