Size Really Does Matter!

As much as you might like to believe, in the natural world size really does separate the winners and the losers. From interspecific competition to global geochemical cycles the size of the earths inhabitants can have a profound effect on the way ecosystems function. There is a need to study the relationship between size and function in order to predict how communities will change in the future and the effect of this on our planet.

Many animal species exist in groups or at large population densities in relatively small areas. Often within these groups there can be and order of dominance or and assignment of roles. One of the most familiar examples of this are in primates. Because this family is so close to our own, in fact we belong to the same family as the great apes Hominidae, we have developed an interest in their social structure and they have become synonymous with research worldwide across many disciplines. Primates are advanced mammals with complex social structure. Many primates exist in groups where some form of dominance is established. Often the most dominant member is the largest or oldest male or female. This pattern can be seen throughout the animal kingdom from elephant seals to British Deer. The largest member comes in to dominance often through brute force and can be ousted at a later date. The biggest and strongest individuals get the best mates, the best feeding grounds and therefore create a loop where they continue to be the strongest by having access to the best resources.

Even in altruistic communities size is important. These organisms all serve together for the benefit of one individual who has become dominant, being born with a silver spoon in their mouth. Queen ants and bees have been born in to royalty and fed only the finest of foods. Therefore the dominant individual is usually the largest and the larger the colony they rule over, the more offspring they can raise and more successful they become.

Occasionally it is not beneficial to the organism to be larger, but the benefits may be transmitted to others such as us humans. An example of this occurs in our marine world, our oceans contain vast numbers of microscopic organisms called phytoplankton. These singled celled algae transform the suns energy in to energy for survival via a process known as photosynthesis. They are crucial to the functioning of the planet producing almost half the oxygen in our atmosphere and making up the base of marine food webs, from the fish we eat to the ocean giants. It is an understatement to say that these creatures are vital to life on earth. However new studies have shown that the size of phytoplankton is reducing in response to climate change and ocean acidification (Finkel et al., 2010). This not only leads to a reduction in primary productivity in our oceans but also has significant implications on our oceans ability to sequester carbon. If you follow the story of climate change you may be familiar with the fact that our oceans can absorb excess CO2 from our atmosphere, acting as a carbon sink and potentially combating climate change. However its not just a case of CO2 dissolving in to the ocean, the carbon is absorbed by the phytoplankton and fixed in to their framework. Phytoplankton have relatively short life cycles and when they die they sink to the bottom of the ocean, taking the carbon with them. However it has been shown that this only occurs in larger phytoplankton which are heavy enough to sink out of the surface waters. Small organisms are rapidly recycled and the carbon doesn’t easily leave the system (Pesent et al., 2000). Therefore if phytoplankton are getting smaller then there is less of a carbon sink in our oceans. This reduces the oceans ability to sequester carbon and can potentially accelerate climate change further.

Courtesy of my good friend and artist Laura @phytoplanktonic

And so there will always be winners and losers, however the winners are those with that little bit extra…. in this case size! With an unpredicatable and possibly turbulent future, it is important that we consider what makes a winner and what impact environmental changes will have upon this. We need to follow these impacts through the ecosystem identifying knock on effects which will most likely uncover that even the smallest changes can have potentially catastophic impacts on the earth as we know it.


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