David Beeson, late August 2021
It could be argued that wildlife enthusiasts spend too much time looking and too little in thinking. I bet you disagree! Sure, I do. The sights and sounds of the natural world is alluring and gives me a buzz. I am never more content than exploring for the unknown or simply enjoying magnificent redwoods, oaks or a green scene. Yet, there is more to be had. Why is that plant there, but not living two kilometres away? How can a mole live underground, while a similar sized rodent needs the open atmosphere? That is ecology and ecology depends on the chemistry of the environment and the organism.
Oxygen ecology
Moles, bloodworms (Chironomid larvae, non-biting midges) and vicuna have the same problem. They dwell in oxygen-deficient places. Moles underground, the bloodworm in the mud of aquatic places and the vicuna high in the mountains. Oxygen is the vital component in aerobic respiration – the release of energy from organic materials that drives the organism’s metabolism. (Anaerobic energy release is less efficient and leaves potentially toxic end products such as ethanol or lactic acid.)
Atmospheric oxygen decreases with height and so the gradient from the air to the vicuna’s blood capillaries in its lungs is lower – and diffusion could potentially not supply enough for its needs. Blood’s oxygen-carrying pigments can combine with diffused oxygen and carry it away from the lungs, so maintaining a good diffusion gradient. That oxygen is then dumped (released) where the local oxygen concentration is low. There is a graph that explains this – the oxygen-dissociation curve. This varies with different oxygen-carrying blood pigments. Haemoglobin (Heme for you Americans) is less willing to pick up oxygen than myoglobin, for example.
Here I need to divert to chickens. How would you know if a butcher sold you leg or breast chicken meat? Colour. That’s because chicken legs work aerobically and to run away from a foxy predator they have an oxygen storing pigment, myoglobin, fixed in their muscles. Explosive flight, when the fox is just too close, is anaerobic and so breast (flight) muscle has no fixed myoglobin and is white. (Now you know why some supermarkets shine red light onto their beef displays – because beef also has myoglobin and the public seemingly believes the more the better.) Have you noticed how deeply coloured heart muscle is? Not sure about you, but the more oxygen reserves in my heart the better.
Myoglobin picks up oxygen better than haemoglobin, yet only releases it when body oxygen levels are low. Ideal for the vicuna and the mole.
A baby needs to change its blood haemoglobin type soon after birth as the oxygen conditions from the womb to air have changed.
Bloodworms can be very different organisms because this is a loose non-scientific name. Midge larvae and small aquatic (earth) worms have the same common names. Both habit oxygen-deficient, muddy environments and need haemoglobin-like pigments in their blood, while open-water relatives do not. Mud is both dense and absorbing of oxygen as organic material decays, but open water draws oxygen from its surface, so is richer. Open water livers do not need to waste resources in having the extra oxygen carriers. Different chemical conditions, different physiological answers.
There are many oxygen-carrying or holding pigments, even in plants such as legumes – that need it to aid nitrogen fixation.
Acidity ecology.
On one occasion I set my students to assess the numbers of earthworms in two different environments – a lawn and later an acid heathland. The technique was learned on the lawn first and the latter was on a field trip. They marked out a area with a quadrat and poured a mildly irritating chemical onto the soil. Worms move to the surface under such conditions and can be captured washed and counted. (You can do the same with a solution of mustard in water.) On the heathland they found no worms. Worms cannot cope with acidic soils, which partly explains why the humus does not become incorporated into the subsoil.
pH, the scientific measure of acidity, varies. pH 3.5 (acidic) or less is known and at the other extreme pH 9 (Alkaline). Most plants live in the pH 5.5 – 7.0 range.
Soil is composed of water, air, humus (decaying organic materials), rock particles and living organisms. The rock particles can decay and release their chemical components or surface chemicals can be released by chemical action or water flow. These chemicals may be needed for the plants’ metabolism, especially nitrates (or similar), phosphates and potassium (N, P, K) but also numerous other micro-nutrients (iron, manganese, cobalt etc). As the soil pH changes so these chemicals are held or released in various proportions, and there may be too many or too few for any specific plant. For example, calcicoles need to grow in calcium-rich soils, calcifuges where calcium is lacking. Calcicoles are found on chalky or limestone areas, calcifuges are not there but on acid heathlands where the calcium is leached out by the acidity.
In Wareham Forest the soils are acidic, yet the roadway through it was made from calcium-rich marine gravels and the flora is strikingly different.
As global carbon dioxide increases it enhances sea acidity and this can adversely affect the shell composition of molluscs and corals… it dissolves away. Atmospheric acidity impacts on lichens and their tolerance determines where they survive. Xanthoria, the yellow lichen often spotted on roofs, is quite acid-tolerant and is encouraged by bird excrement, so occurs frequently in urban places.
Life in the gut and other exciting places.
Of course, living in or from another organism poses more chemical issues. We will avoid Covid-19 and the chemical mechanisms of immunity or disease or death, but the alimentary canal is filled with acids (human stomach) and digestive enzymes designed to kill and break down organic matter. Our gut flora will need either a wonderous body coating or chemicals to neutralise their opposition. I well recall my first dogfish dissection, for its body cavity and gut was filled with parasitic worms. What a difficult spot to call home.
Okay, now where else do you not fancy living? As a bacterium on human teeth? A dung or sewerage works specialist? You’ve got it … the point I am making is that chemistry is always needed if the organism is to survive, and we know little or nothing about it. Now there are some great research projects for new graduate biologists or chemists.
So, give chemistry a thought. All organisms only work because of their chemistry. Biochemistry is the chemistry of life.
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Wildlife and Ecology, the Wildlife Encyclopaedia 