There are many estimates on biodiversity described much better than I can do by Zoest (1998). We know some 1.7 million well-described species but much more are unknown while some 100 000 species are lost since Linnaeus. The extinction rate is estimated 1000 per year now; the growth in evolution as 1 successful species per year. Though we now know the genome of some, we do not know yet how they work let alone we know their mutual relations. Even how our own species works is nearly completely unknown to us, though we already studied 3000 years on this topic. Having some success in medicine, we seldom understand exactly why. Compared with the combinatory explosion of unanswered questions we understand almost nothing, otherwise we could invent species. Possible principals punish researchers admitting that honestly and modestly. Mythmakers win the competition. However, myths may be useful for survival.
Every state bears its own responsibility in this multitude of species like a modern Noah. Though The Netherlands occupies less than 0.01% of the earth’s surface it entails approximately 35 000 (2%) of the earth’s number of known species. Our responsibility is proportional to their global, continental (blue list), national (red list) or local rarity.
The concept of rarity and thus responsibility is scale-sensitive.
Depending on the definition of health1 I estimate that roughly 80% of the human population is unhealthy. There are positive and negative relations between human health and biodiversity. The impact of biodiversity on human health is unknown. Perhaps a small organism in some square kilometres of the remaining rainforests is on the long term a necessary condition for our life by producing tiny quantities of chemical compounds conditioning processes in our body and mind as catalysts, but we do not know. How to calculate the risk of loosing them?
The reverse impact of human health and growth on biodiversity is better known but not certain.
Fig. 1 Estimated growth of world population
Health is a scale dependent concept in time. Though world population is not healthy on an individual level, in the long term we are a healthy species growing in numbers exponentially ousting other species, living twice as long than some centuries ago.
And we are not only expanding in number. Per person we need more and more living space in our homes and neighbourhoods. In a wider context we reduced the space we need for agriculture reducing biodiversity in rural areas at the same time.
Intensity of use
However, some 20 years ago Jong (1985) found the intensity of urban use in The Netherlands was highest in shops (135 hours/m2year). After shops came offices, social-cultural facilities, schools, home and garden (48 hours/m2year). The other hours of the year (counting 8760 hours) in the urban surface may be available for other species depending on the conditions we leave them by design and use (distinguished by time scale). Some species accept or even welcome our presence like that in step vegetation (for example greater plantain, rats, mosquito’s, sparrows). Could we welcome more rare species in our towns by creating ecotope cities or as Tjallingii (1996) stresses ecological conditions? How does it interfere with our health?
Londo (1997) considered diversity as a risk-cover for life. In the diversity of life there was always a species to survive or within a species a specimen that survived. Survival of the fittest presupposes diversity from which can be ‘chosen’ in changed circumstances. Diminishing biodiversity means undermining the resistance against catastrophes. From the 1.7 million species we know, we probably lost some 100 000. So, we not only introduce ecological disasters, but we also undermine the resistance of life against these disasters.
The curve of ecological tolerance relates the chance of survival of a species or ecosystem to any environmental variable, for instance the presence of water. In that special case survival runs between drying out and drowning (Fig. 2 ).
Imagine the bottom picture as a slope from high and dry to low and wet. Species A will survive best in its optimum. Therefore we see flourishing specimens on the optimum line of moisture (A). Higher or lower there are marginally growing specimens (a). The marginal specimens however are important for survival of the species as a whole.
Fig. 2 Ecological tolerance in theory and reality.
Suppose for instance long-lasting showers: the lower, too wet standing marginal specimens die, the flourishing specimens become marginal, but the high and dry standing specimens start to flourish! Long-lasting dry weather results in the same in a reversed sense. Levelling the surface and water-supply for agricultural purposes in favour of one useful species means loss of other species and increased risk for the remaining.
But there is a less friendly ecological lesson hidden within this scheme. Marginal specimens are important for survival of the species as a whole. A reservoir of unhealthy specimens favours species. Death regulates life. Health is also spatially scale-sensitive.