Periodically I come across an article that announces a new level of depth discovered within terrestrial ecosystems, previously unknown interactions that singularly or through accumulation lead to significant changes in local biodiversity.
I was first made aware of the sheer depth of complexity throughout global environments during a third year module, ‘Conservation Biology’. This course introduced me to various new levels of ecological phenomena. In this post I would like to share a few such examples of environmental complexity using case studies that have interested me.
One such set of complex interactions is encompassed by the relatively new theory of indirect ecological effects. This theory states, in its simplest form, that one species can influence another that it has no contact with, due to both species interacting with a third mutual species (1). Such interactions have been demonstrated for instance between aphids, barley, rhizobacteria and parasitoid wasps. Here, the genotypes of the aphid and barley, as well as the presence/absence of rhizobacteria were found to differentially impact upon wasp fitness. Importantly it should be noted that whilst these indirect ecological effects span across 2 (or potentially more) species, the magnitude and direction of this effect is meditated by the genotypes of intermediate species.
The awareness that a species genotype can determine both the presence and phenotype of the biota with which it interacts, has serious implications for conservation. After all, in order for the outcomes of potential conservation schemes to be successfully predicted, all connections within ecosystems must be understood.
Another recent publication drew my attention towards a different set of interactions. It is well known that rich microbial communities live around plant roots, feeding of their photosynthetic exudates. Whilst certain communities of microorganisms (e.g. mycorrhizal fungi) have been extensively studied, and their interactions mapped, other symbiotic relationships remain mysterious.
One such state of symbiosis is the occurrence of disease suppressive soil, a phenomena studied in detail by Mendes et al., 2011 (2). His study identified, to my knowledge, the first example of microbial soil communities suppressing disease onset in a plant species. Interestingly disease suppression was concluded to be a result of specific concoctions of bacterial taxa. In other words the relative abundance of different taxa, not the presence or absence of specific groups, is the strongest indicator of disease suppressive soil. Moreover, further tests identified that many strains which lacked disease suppressive qualities in isolation, could work in synergy with other taxa within their micro-community to have an active effect.
With many thousands of microbial taxa in any one area, these synergic effects are impossibly hard to predict. Any one microbial genotype can interact with thousands of others, through an astronomical number of pathways that can lead to a massive variety of outcomes.
The final study I would like to talk about was enticingly titled ‘Alien worm invasion threat to forests’ on the BBC news website. Not surprisingly then, it concerns the threats of human induced earthworm migration on forest ecosystems (3).
The threat of invasive species is not a new one, nor is the realization that such problems are exacerbated by human transport of these species.
The problem with earthworms however, lies within how the public perceives these animals. Reputed for their roles in nutrient and mineral cycles, as well as in organic decomposition, many regard worms as healthy components to ecosystems, however this is not universally true. Some environments lack native earthworm species, a result of historical geological events. As such these ecosystems have not evolved to cope with the ecological consequences of invasive earthworm activity (4).
Negative effects reported from earthworm invasion include alteration of carbon and nitrogen cycles, acceleration in leaf litter composition and increased rates of soil erosion. Such alterations of natural cycles have the potential to alter entire ecosystems, threatening the biodiversity that exists within them (4).
To combat these threats, the authors believe it is first necessary to build public awareness around the issue at hand. The study referenced, identified that just 21% of earthworm users (e.g. fishers) were aware that the animals were invasive and as such, were happy to simply release them into the environment. Moreover, none intentional transportation of worms e.g. via grooves in car tires is also a significant source of translocation.
The authors suggest that challenging these misconceptions and empowering the public to ‘implement behavior that helps mitigate the introduction of earthworms’ is the best solution to tackling the threats of invasive earthworms (4).
In reality however, invasive species, once established are particularly difficult to dislodge, and the cost in monetary value as well as in man hours can be considerable.
This blog has discussed just a few examples of environmental complexity that I have come across. Indirect ecological effects, synergy within microorganism communities and the threats of invasive species. Interestingly, all the case studies I have mentioned have only been introduced to the scientific community within the last few years. This highlights just how quickly this field of ecology is growing, as well as how little we know about the subtle, dynamic interactions that determine the conditions of the ecosystems on which our species are sustained.
With incremental changes to ecosystems having demonstrably significant effects on biodiversity, the impacts of large-scale human manipulation is likely to have been underestimated by many.
Current trends of increasing extinction rates across plant and animal classes are set to continue whilst scientific knowledge struggles to catch up with, and repair the damage caused by human actions.
(1). Zytanska et al Ecology, 91 (6), Community genetic interactions mediate indirect ecological effects between a parasitoid wasp and rhizobacteria, 2010, pp. 1563-1568
2. Mendes et al., Science, 332, 2011, pp 1097-1100
4. Dara E. Seidl & Peter Klepeis, human ecology, 2011 Human Dimensions of Earthworm Invasion in the Adirondack State Park.