Science Literature

People who love the countryside and open places tend to value biodiversity and rich ecosystems. There is a perception that a high species diversity helps to stabilise ecosystems by buffering the effects of environmental change, and in addition create ecosystems with greater functionality. According to MacDougall et al. (2013), "Biodiversity can stabilize ecological systems by functional complementarity, with different species thriving under different conditions." However, scientific underpinning has lagged behind tacit knowledge and we are faced with the growth of monocultures in agricultural husbandry and commercial land use. Nevertheless, the situation is changing, and the benefits of biodiversity are being increasingly recognised. Researchers face the problem of complex patterns of human interventions.

"Human land management is often persistent, by intentional (for example, fire suppression and overfishing) or inadvertent (for example, nitrogen pollution) disturbances that homogenize both resident diversity and environmental conditions. Persistent disturbances obscure diversity-stability relationships because they can affect ecosystem function independently of diversity, as when overgrazing directly decreases production and provides opportunities for invasion. Because persistent disturbances can also drive species loss, false positives may arise between diversity and ecosystem function, in which reductions in diversity and function are correlated but have weak mechanistic connections." (MacDougall et al. (2013), page 86)

"Biodiversity is vital for our survival and is a key measure of the health of our planet." (Source here)

Two studies have been published recently that develop the themes of (1) biodiversity promoting more resilient ecosystems, and (2) biodiversity expanding the functionality of ecosystems. First, we consider the issue of resilience.

The study area is in the Pacific Northwest of North America on grasslands described as oak savannah. Human influence has resulted in a loss of plant diversity but an increased yield of grass production. The grasslands are said to remain "resilient to invasive species and climate fluctuation". The research programme involved the periodic burning of experimental plots followed by recovery. The results show that grasslands "were able to recover from burning only in areas that had a relatively high diversity of native plants". By contrast, the species-poor grasslands were rapidly invaded by tree species with the resulting collapse of the savannah ecosystem.

"Our work demonstrates how persistent human activity can homogenize the structure and function of ecological systems, while simultaneously weakening diversity-related compensatory mechanisms needed to respond to sudden disturbance. These findings are consistent with previously demonstrated connections between diversity and ecosystem function, in which a larger portfolio of functional strategies within a community provides insurance against sudden environmental change. Given that many terrestrial systems possess this signature of compositional homogenization owing to persistent human activity, there may be a similar vulnerability to sudden environmental change that will be only evident after the collapse occurs." (MacDougall et al. (2013), page 88)

The second study was concerned with trees, and particularly with the link between ecosystem diversity and ecosystem services (functions). Again, tacit knowledge has recognised the connections before being able to document them by rigorous research.

"Ecosystems provide a wealth of benefits to human society, and the provision of such ecosystem services depends fundamentally on functions performed by organisms. This has led scientists to enquire how the diversity and composition of communities may regulate ecosystem functions. A large body of evidence has established that species diversity promotes ecosystem functions under experimental conditions. There are, however, many exceptions to the positive diversity-function relationship." (Gamfeldt et al. 2013, page 2)

The need is for research designed to look at multiple functions at a regional scale, leading to a more holistic assessment of an ecosystem. The researchers studied plots in production forests. These were relatively species-poor. The maximum recorded was 10, and only 1.5% of the plots hade more than 5 species. They identified six ecosystem services, including tree biomass production.

"Our results from boreal and temperate production forests show that the relationships between tree species richness and multiple ecosystem services were positive to positively hump-shaped, and that all services attained higher levels with five tree species than with one species. Although the relatively high level of tree biomass production with five compared with one tree species may seem both impressive and surprising, we note that similar effect sizes have been found previously. [. . .] There are, unfortunately, no previous studies on the relationships between tree species richness and the other five services that allow for comparisons with our findings." (Gamfeldt et al. 2013, page 2,3)

The paper has an interesting discussion of trade-offs leading to an explanation as to why diversity should be more prominent in strategic thinking in forestry.

"[O]ur results suggest the importance of tree species mixtures for the continued provisioning of ecosystem services from the 2-billion hectares of forest in the world currently managed as production forests or used for multiple purposes (55% of all forests). [. . .] Although the trade-offs we found imply that it will be difficult to maximize all ecosystem services simultaneously at the stand scale, the positive relationships between tree diversity and individual services suggest that adjacently located monocultures would not optimize the provision of ecosystem services at the landscape scale. Instead, adjacent stands, each with multiple species but in different combinations, might be the best way to provide multiple ecosystem services at the landscape scale." (Gamfeldt et al. 2013, page 4)

Some of the deeper issues relating to diversity are explored further below. Research findings are now complementing tacit knowledge that diversity is beneficial for ecosystems and for agriculture. This means that diversity promotion should be an integral part of the different ways we interact with ecosystems - whether for husbandry or for conservation. In other words, 'diversity by design' should be the way we think about human intervention. We might also reflect on 'diversity by design' without human intervention. This means that if the ecosystems we see around us witness to an intelligent Designer, then 'diversity' is a keyword. If this avenue of thought is valid, the inference can be made that mechanisms will exist for promoting diversity. We may then envisage machinery for engineering ecosystems to match environmental constraints. This leads to a highly dynamic perspective of organisms and one that confronts some very stereotyped popular views about design thinking.

The stereotype was advanced by Charles Darwin in his On the Origin of Species. Darwin claimed that if animals and plants were created, they would not display changes. Belief in a Creator, he argued, leads to a doctrine of fixity of species. So any evidence of variation was used to argue for evolution ("my theory") rather than creation. He wrote (Chapter XIV, Page 458): "Authors of the highest eminence seem to be fully satisfied with the view that each species has been independently created", but nowhere did Darwin support this statement with quotations or references to scholars who upheld the doctrine of the fixity of species. He asserted it, and his readers soaked it all up. It has been endlessly repeated over the years, and is part of school textbooks - so the next generation of students is programmed to think like Darwin. The reality is that the fixity of species was not held by scholars contemporary with Darwin. For example, Darwin should have known that his creationist mentor, Professor John Stevens Henslow, had embarked on a research programme to probe the limits of variation of selected plants (Kohn et al. 2005).

If we start with evidence (that diversity is beneficial) and infer that mechanisms exist for promoting diversity, then we will approach the observational data quite differently from Darwin and the Darwinists. We will recognise mechanisms that deliver diversity (e.g. via recombination of DNA during sexual reproduction). We will find that the genome exhibits plasticity, so that many phenotypes can emerge from the same genotype. Scholars today are developing understanding of phenotypic plasticity - a phenomenon that owes nothing to Darwinism. For more on this topic, go here. For case studies, go here and here.

'Diversity by design' is a rational and reasonable starting point for the study of ecology. Those who set out with this perspective will find that they travel along a different path from the one taken by Darwin, and it leads to quite different conclusions. This is a Kuhnian paradigm shift. Dominant and recessive genes are the tip of the iceberg! Speciation that is rapid, rather than gradual, is an indication of diversity by design. When we find non-random mutations or mutation hot spots, these are pointers to designed mechanisms. Epigenetics has the potential for expanding our understanding of the ways for diversity to develop. The more diversity by design is probed, the more it presents itself as a viable and interesting research paradigm.

Diversity loss with persistent human disturbance increases vulnerability to ecosystem collapse
A. S. MacDougall, K. S. McCann, G. Gellner & R. Turkington
Nature, 494, 86-89 (07 February 2013) | doi:10.1038/nature11869

Long-term and persistent human disturbances have simultaneously altered the stability and diversity of ecological systems, with disturbances directly reducing functional attributes such as invasion resistance, while eliminating the buffering effects of high species diversity. Theory predicts that this combination of environmental change and diversity loss increases the risk of abrupt and potentially irreversible ecosystem collapse, but long-term empirical evidence from natural systems is lacking. Here we demonstrate this relationship in a degraded but species-rich pyrogenic grassland in which the combined effects of fire suppression, invasion and trophic collapse have created a species-poor grassland that is highly productive, resilient to yearly climatic fluctuations, and resistant to invasion, but vulnerable to rapid collapse after the re-introduction of fire. We initially show how human disturbance has created a negative relationship between diversity and function, contrary to theoretical predictions. Fire prevention since the mid-nineteenth century is associated with the loss of plant species but it has stabilized high-yield annual production and invasion resistance, comparable to a managed high-yield low-diversity agricultural system. In managing for fire suppression, however, a hidden vulnerability to sudden environmental change emerges that is explained by the elimination of the buffering effects of high species diversity. With the re-introduction of fire, grasslands only persist in areas with remnant concentrations of native species, in which a range of rare and mostly functionally redundant plants proliferate after burning and prevent extensive invasion including a rapid conversion towards woodland. This research shows how biodiversity can be crucial for ecosystem stability despite appearing functionally insignificant beforehand, a relationship probably applicable to many ecosystems given the globally prevalent combination of intensive long-term land management and species loss.

Higher levels of multiple ecosystem services are found in forests with more tree species
Lars Gamfeldt, Tord Snall, Robert Bagchi, Micael Jonsson, Lena Gustafsson, Petter Kjellander, Maria C. Ruiz-Jaen, Mats Froberg, Johan Stendahl, Christopher D. Philipson, Grzegorz Mikusinski, Erik Andersson, Bertil Westerlund, Henrik Andren, Fredrik Moberg, Jon Moen & Jan Bengtsson.
Nature Communications, January 2013, 4, 1340 | doi:10.1038/ncomms2328

Abstract: Forests are of major importance to human society, contributing several crucial ecosystem services. Biodiversity is suggested to positively influence multiple services but evidence from natural systems at scales relevant to management is scarce. Here, across a scale of 400,000 km2, we report that tree species richness in production forests shows positive to positively hump-shaped relationships with multiple ecosystem services. These include production of tree biomass, soil carbon storage, berry production and game production potential. For example, biomass production was approximately 50% greater with five than with one tree species. In addition, we show positive relationships between tree species richness and proxies for other biodiversity components. Importantly, no single tree species was able to promote all services, and some services were negatively correlated to each other. Management of production forests will therefore benefit from considering multiple tree species to sustain the full range of benefits that the society obtains from forests.