November 1, 2010 | 4
Why are we approaching biodiversity conservation from such different points of view?
We are currently rounding out the year 2010, proclaimed by the U.N. as the "International Year of Biodiversity." While the recognition of the importance of nature is extremely valuable, I’m left at a loss as to what a "year of biodiversity" really means.
Biodiversity is most often defined as the ‘number of species present in a given area’; however, to refer solely to the number of organisms present leaves out the most important aspect of any ecosystem: how these organisms interact. A simple species catalogue gives no indication about the relationships between organisms despite the fact that such relationships play a key role in shaping biodiversity. Researchers of biodiversity are rarely interested in the mere identification of species, they instead ask questions and gather data about how communities work – which is what will ultimately lead to effective maintenance of ecosystem biodiversity.
For example, a large-scale field study of plant-herbivore interactions in the forests of New Guinea undertaken by Novotny et al (2010) documents the abundance of feeding relationships in this complex food web. Over almost a decade of detailed field sampling, these researchers were able to identify 6,818 feeding links between 224 plant species and 1,490 herbivores, a feat that has yet to be repeated in studies of biodiversity. Though this work represents an almost unfathomable amount of effort, it is suggested that these figures may only represent 15 percent of total herbivore richness and interaction diversity in these lowland forests (Lewinsohn 2010).
Documentation of feeding links is a great place to begin mapping a food web, but it does not take into account the multitude of other possible interactions between species.
A study of biodiversity in the backwater lagoons of Jamaica illustrates this point beautifully. When threatened by predators, the sea urchin Tripneustes ventricosus affixes live snails (Cerithium litteratum) to the outer surface of its test. Urchins have been shown to pick up ten times as many snails in the presence of their predators, demonstrating the success of this technique as a predator deterrent (Coleman 2010). Snails that are picked up by urchins gain 47 percent less weight and have 75 percent less shell thickness than those that are unassociated with urchins; however, their overall survival rate is three times higher. Despite the fact that the snail-urchin interaction does not involve direct feeding (and would thus be missed by food web mapping) this relationship has direct benefits to the survival of both the urchins and snails, and is therefore an important component of the biodiversity of this ecosystem.
Another important consideration for studies of ecosystem biodiversity is an organisms’ role may not remain static through its lifetime. Unlike humans and many other mammals, most invertebrates, amphibians, and fish have markedly different behaviors as juveniles than as adults. This means that the potential for interactions between varying developmental stages of different species is virtually limitless!
A recent study on the relationships between spiders and grashoppers in North American forests illustrates that both predator/prey relationships and associated indirect effects are subject to the developmental process (Barton 2010). Nymphal grasshoppers (Melanoplus femurrubrum) are negatively affected by predatory spider (Pisaurina mira) presence; smallest instars experience the most negative effects, and adults are unaffected. Threatened nymphs feed on herbs instead of their preferred grass-based diet, which in turn has a positive effect on the grass community. Interestingly, when communities were experimentally warmed to simulate conditions of a changing climate, nymphal grasshoppers were no longer negatively affected by the predatory spiders. In the face warmer temperatures, spiders retreated to lower areas of the canopy, releasing the grasshoper nymphs from predation and indirectly harming the grass community (upon which the predator-free nymphs preferred to feed).
No organism is an island, isn’t that right?
The underlying message in the above examples is that interactions between organisms are diverse, complex, and certainly play a major role in defining the biodiversity of any ecosystem. Why then, is a current ‘conservation’ strategy aimed at preserving biodiversity completely ignoring their existence? "Managed Relocation" (MR), is a conservation strategy that has been gaining momentum in the past few years. It involves artifical expansion (via human intervention) of species’ ranges in the face of global climate change. Approximately 35 percent of all species could be at risk for climate-driven stress (Thomas et al. 2004), and proponents of MR suggest that the mere creation of parklands or nature reserves will not be enough to ensure their survival. Species that are unable to adapt to quickly changing environmental conditions, or species that physically cannot expand their ranges due to human-generated barriers like cities, are candidates for MR.
A recent review (Minteer and Collins 2010) suggests that the unprecedented stress being inflicted on natural ecosystems world-wide is enough to merit a significant change to traditional "Parks and Preservation" conservation strategies. It argues that the only alternative to implementing MR is widespread species extinction. The review outlines key areas for consideration of MR in any particular context, including how candidate species are chosen and the assignment of authority figures for species relocations. Though the idea of MR has become fairly widespread, there is little consensus about just how such a strategy could actually work.
"If we value wild species and wish to bequeath a significant fraction of global biodiversity to future generations, radical strategies like managed relocation may well be our last best chance." – Minteer and Collins 2010
Despite the lack of a consistent framework, there are several places where MR is already being practiced. A test study of two British grass-feeding butterflies (Melanargia galathea and Thymelicus sylvestris) was initiated in 2000 in order to test the effectiveness MR as a conservation strategy (Willis et al. 2009) since neither species is expected to be able to "keep up" with rapidly changing climatic conditions. Climate response surface models were used to extrapolate areas beyond the existing ranges that would be climatically suitable, and approximately 500 individuals of each species were individually caught and transferred to their relocation sites in Northern England. Both species relocations were deemed to be "successful" based on healthy, expanding populations for the next 8 years, leading the authors to proclaim that MR has the "potential to be a useful conservation tool to help limit the impacts of climatic change on species of conservation concern" (Willis et al. 2009).
An assisted migration adaptation trial (AMAT) has been on-going in the forests of British Columbia for just over two years (Marris 2009). Seedlings from 16 species of coniferous trees were taken from several spots in British Columbia, Washington, Oregon and Idaho and re-planted in several new sites in order to investigate the possibility of creating populations where they do not currently exist. Forest health in British Columbia has been drastically comprimised in the past decade due to uncontrollable outbreaks of the mountain pine beetle (Dendroctonus ponderosae). Ironically, the devastating pine-beetle outbreaks are themselves a product of global climate change. The AMAT is being implemented in order to mitigate the losses of several coniferous species whose ranges are predicted to stretch northward in the coming century. The rationale for both examples of MR in action remains the same: if species are unable to move themselves to suitable (future) climates, MR represents a way to prevent their extinction.
So how do those of us interested in biodiversity conservation reconcile these dichotomous points of view? Minteer and Collins (2010) have got a point: there is no denying that without the drastic practice of MR, we are likely to see the extinction of many species. However, the question remains: what is the most important aspect of biodiversity: 1) the species count or 2) the interactions that created the community in the first place? Is the answer somewhere in the middle?
No it’s not.
The answer lies in the beauty of the biology, and frankly MR ignores biology completely. By "saving" a given species through managed relocation, we are quite likely endangering many others. Studies of biodiversity do not treat organisms as independent entities, but studies of managed relocation do. Many species are going to go extinct in the face of global climate change – the damage has been done there’s nothing that can change it now. However, a greater number of species will be affected (in unknown ways) by ignoring the role of interactions in conservation management and placing species where they don’t belong. MR is therefore an impossible strategy for maintenance of biodiversity.
Barton, Brandon T. 2010. Climate warming and predation risk during herbivore ontogeny. Ecology 91:2811–2818.
Coleman, H. 2010. Complex species interaction in tropical backreef communities. Journal of Experimental Marine Biology and Ecology 393: 124-129.
Lewinsohn, T.W. 2010. A large trophic quilt. Journal of Animal Ecology 79:1143–1145
Marris, E. 2009. Planting the forest of the future. Nature 459: 906–908.
Minteer, B.A. and Collins, J.P. 2010. Move it or lose it? The ecological ethics of moving species under climate change. Ecological Adaptations 20: 1801-1804.
Novotny, V., et al. 2010. Guild-specific patterns of species richness and host specialization in plant–herbivore food webs from a tropical forest. Journal of Animal Ecology 79:1193–1203.
Thomas, C. D., et al. 2004. Extinction risk from climate change. Nature 427:145–148.
Willis, S. G. et al. 2009. Assisted colonization in achanging climate: a test-study using two U.K. butterflies. Conservation Letters 2:45–51.
The views expressed are those of the author and are not necessarily those of Scientific American.
ABOUT THE AUTHOR:
Carin Bondar is a biologist, writer and film-maker whose work has appeared on Discovery Network, Discovery World HD and online at National Geographic Wild. A former ballerina, she now holds a PhD in community ecology from The University of British Columbia. Her thesis work took her to the temperate rainforests of British Columbia and New Zealand where she researched community interactions of invertebrates in small streams. Dr. Bondar blogs at www.carinbondar.com, tweets as @drbondar, and has just released her first book The Nature of Human Nature. When she’s not absorbed in the wonderful world of biology, she is a busy mom of three young children.