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