Arguments published, in order:
Complexity, ecosystem . . .
Design of vertebrate eye
Expanding forests . . .
Complexity, ecosystem and the art of the soluble
A pond, a meadow and a forest, in Poland. Photo credit Wikipedia
This photograph illustrates three characteristics of a central European landscape that in popular speech are often called ecosystems. A scientific and formal definition of an ecosystem is more difficult. The boundaries of the forest are vague. How many species of the forest are included in this system - all the trees, but what about all the smaller plants and the microbial life of the soil? System implies functional interconnections between most or all parts of the system but in the vast assemblage of species within a forest how can this be possible? The complexity of it all seems overwhelming. Some ecologists simply use the term assemblage instead of ecosystem, avoiding the implications that system has of something designed and operated by people.
The alternative perspective for gaining understanding of how a lake or meadow or forest works as a whole is to study its parts, as defined by those species that are accessible to be counted, measured and weighed. How those species might interact with others close by is best understood by studying how they have evolved by natural selection to survive and reproduce well within the forest. Examples of how ecological complexity can be approached to provide useful understanding of the dynamics of forests and other parts of the landscape are discussed in this argument.
For the full version of this argument: 'Complexity, ecosystems and the art of the soluble' download here.
Good or bad design of the eye of vertebrates?
Human eye. Credit: Petr Novák, Wikipedia
The eye is the most important sense organ for us humans. It is very well studied for medical reasons and eye has been important in the development of ideas about how life evolved. One aspect of studies on the evolution of our eyes and those of vertebrate animals generally is the proposition that the design is poor when compared to cameras. If the evolved design is poor, then it cannot be the work of an intelligent designer. Not only is the vertebrate eye compared unfavourably to cameras but also to the eye of squids and octopuses.
Seemingly the problem with our eyes is that the light sensor, the retina, is the wrong way round! The photoreceptor cells, face away from the incoming light. Bad design? Moreover, they are covered with layers of nerve cells and blood vessels. An octopus has eyes with the photoreceptor layer facing towards the lens, and with the nerve cells going beneath this layer as they lead from the retina to the brain.
Our eyes work well because of the inverted retina, not despite it. The problem of obstruction by nerve fibres and blood vessels is solved at the spot where light is naturally focussed. Here the layer of nerves is thin and the blood vessel layer is reduced. Our retinas have the highest demand for oxygen of any tissue in our bodies. To supply the retina there is a special blood system as network of small vessels that envelope the outside of the eyeball and press against the outermost retinal layer providing a very high rate of exchange with the retina. This entire adaptation for vision of high information content is physically possible only with an inverted retina.
For the full Argument, with references download the file here:
Are the world's forests really expanding?
Forest cover in part of North America mapped using satellite data; yellow to blue = least to most.
Newspaper and television reports of deforestation and forest fires in the context of the climate crisis are dramatic and depressing. But is this the whole story or is there more happening to forests at the global scale that is cause for optimism and incentive to action? Yes is the short answer, but as often with anything ecological the story contains accounts of reliable research that seem contradictory. This essay presents the case for optimism when these varying studies are balanced against each other for a global perspective based on three mechanisms by which forests can expand.
Growth of plants depends on photosynthesis which requires light, carbon dioxide, water and mineral nutrients. The CO2 is a scarce nutrient for plants but increasing in concentration in the atmosphere. This increase is equivalent to a fertilizer for growth and can be demonstrated experimentally and measured as extra biomass as wood per unit area. CO2 is also a greenhouse gas that heats the atmosphere and changes seasonal climates. When leaf-bud in a deciduous forest starts earlier and leaf-fall starts later there is a greening of the forests that can be mapped using data from satellites. The longer the season the greater the annual growth and this can be estimated as mass of wood per unit area per year. A third way in which forests expand is by regeneration on land they formerly occupied or by spread into new areas of land by the hectare or square kilometre.
For the full version download the file here: