The Blink of an Eye

 The lifespan of a human is perhaps 80-90 years and increasing with every generation. That's a lot of living for an organism. It's easy to forget that for most species life is much shorter and much harder. There is a rough rule of thumb that the larger the organism the longer the lifespan the graphic below illustrates this quite neatly.

There are complex ecological reasons for this involving life history strategies and energy flow but in essence, species generally exhibit one of two life strategies. Complex large animals have longer lives than smaller less complex ones. These strategies reflect two extreme modes of reproduction and survivability and can explain why and how different species behave the way that they do.

The two strategies are r and K. r/K selection was developed in the 1960s as part of MacArthur and Wilson's famous theories on Island Biogeography. The theory dictates that species have either an r or a K reproductive strategy. r-strategists are related to the rate of production of a species and so these species produce large numbers of offspring, have short lifespans, and have a low probability of survival. 

K-strategists are dictated by the carrying capacity of an ecosystem, these species have fewer young and live longer. Offspring develop slower and they tend to have higher greater parental care and therefore greater chance of survival.

All this information is pertinent at this time of year as the country erupts in a reproductive fever. Everywhere organisms are mating and having young and it is in this month that one of the organisms that typifies r-selection is abundant.

May is the time in which Mayflies emerge from our rivers in great clouds of dancing pixies. On some rivers, this display of flying mayflies is awe-inspiring but on my patch, it is somewhat subdued. It is still fascinating and this year has been particularly good. There are in fact 51 species of mayfly in the UK and they play an important role in the ecology of a river. They provide food for fish of many species as well as birds given the huge mouthfuls I saw the local Great Spotted Woodpecker taking into its nest.

On my stretch, I managed to identify two species, the Common, or Green Drake Mayfly (Ephemera danica) pictured below and Drake Mackerel Mayfly (Ephemera vulgata). These mayflies have hindwings and three tails. These species may be simple but they are an ancient species, mayflies were around before the dinosaurs, and they are a very successful species.

Most mayflies live but a few hours some as much as a day. I say mayflies, what I actually mean are the adult forms. They emerge from the water in mid-may as dull-winged insects, they then fly into undergrowth and moult again into a much brighter mating form.

The males dance above the water with females darting into the cloud to select a mate where they mate on the wing before the female descends to the water below. She will lay her eggs in the water and then exhausted collapse.

We tend to pity the mayfly's short lifespan but that is only the adult form. The eggs hatch into larvae which will spend up to two years developing on the river bed feeding on algae and vegetation. So feel a little less sorry for the mayfly, yes their appearance to us is fleeting but they in fact have a reasonable life out of sight. The paternal sacrifice of the adults feeds the bellies of fish and birds in a complexly balanced ecosystem. 

And to be philosophical for a moment a two-year lifespan may seem like a blink of an eye to us but this species has lived on earth for perhaps 300 million years whilst Homo sapiens has existed a mere 300,000 years, now who lives in a blink of an eye.

Harmony in nature?

 My long-term camera trapping project whilst giving me fascinating glimpses into animals' private lives also highlights interesting species interactions.

It is surprisingly uncommon for more than one species to appear on camera at the same time. Birds are much more tolerant of each other and so different species can be seen together but mammals are much more wary and when two species do meet it is interesting to see what happens.

For the last few weeks, I thought I had identified two different foxes using the site based on ear patterns. I had 'Speckles' who had orangey specks to the backs of their ears and 'Black-Ears' an individual with completely black ears. It turns out this wasn't as good an identifier as I thought. Two foxes were sighted this week, both with black ears. The interaction between the two was interesting, the last interaction was a post-aggression bout of gekkering but these two individuals seemed much more comfortable with each other.

What was more interesting was the presence of a male muntjac. This youngish male is missing one antler and is present whilst these two foxes are. It seems unconcerned by them but was still wary, you can see it keeps an eye on where they are but is relaxed enough to settle into some grooming. 

This may seem like unusual behaviour for predator and prey but in actual fact, it is unlikely that any fox would actively hunt an adult muntjac. The risk of injury would be too great for a fox to risk, one wrong move and its ability to hunt later could be impaired. Unlike wolves, foxes are not pack animals. They can exist in extended family groups and it's common for two vixens to work together to raise young but this never extends to cooperative hunting. A pair of foxes would have more chance of bringing down a deer but this has never been a hunting strategy. Foxes fill a niche in which they scavenge and prey on rodents and birds, pigeons and pheasants being a favourite.

This clip shows three individuals sharing the same space and time, it's a rare illustration of a certain harmony in nature, a knowledge of eaches position in the ecosystem, and an awareness of the nature of the other.  It is sometimes too easy when wildlife watching to focus on the individual but a better understanding is gained when you consider the individual or the species in the context of the interconnectedness of the habitat. Nature is wonderful and much of that wonder comes from the complexity, thousands of species in an ecosystem reliant on one another woven into an intricate pattern of inter-reactions.