Biodiversity Loss and Cascading Effects

On November 18, 2007 I attended a lecture by Dr. Ricciardi of the MSE entitled “The Future of Biodiversity: How biological invasions and extinctions, driven by human activities, are re-shaping biodiversity on a global scale.” Ricciardi’s talk was split into four parts: He first talked about how many species there are on the planet, then moved to discuss how fast we are losing species, what the causes of biodiversity loss are, and finished by talking about what the consequences of biodiversity loss are.

Most of the presentation was comprised of case studies of biodiversity loss both in Canada and abroad. The two main causes for biodiversity loss are invasive species introductions and land use change (although there are other causes): both driven by human actions. While none of the information was complicated to understand I found that the pace of the talk was a bit too fast and that there was not one clear story to tell, it was just a collection of evidence to support that biodiversity loss is a wide-spread problem. What I found to be the most important part of the talk were the consequences of biodiversity loss: 1) an increase of instability, and reduction in resilience, 2) Loss of ecosystem function and ecological processes. When biodiversity is lost, nutrient and energy transfer in the food chain is disrupted and much of these resources are processed inefficiently, or simply lost within the system. The loss of a or replacement of a species by an invasive can have impacts that cascade through the food web and not only impact the species itself, but every other biotic and abiotic form that it interacts with.

The article that we addressed last week by Finlay and Vredenburg (2007) observed these cascading effects by assessing how trout addition to lakes impacted the mountain yellow-legged frog. While I have always understood aquatic systems to be the ideal study area due to the clear boundaries of a lakeshore (you know what comes in and out), this study proved that the introduction of an aquatic species can have impacts that reach far beyond the shore. Here, the mountain yellow-legged tree frog, a terrestrial species, had fewer food resources (insects) from the pelagic zone of the stocked lakes. The reduced populations of the frogs due to the trout additions, no doubt has consequences for its predators. Many people study how land use impacts aquatic systems (e.x. damming, changing stream courses, pollution, erosion, etc), however perhaps we should start to look at the interactions that run in the opposite direction: how species invasions in aquatic systems can have serious impacts to terrestrial systems. I think that overall, knowing the interactions back and forth between systems (here, land and water) gives more insight to policy makers and managers. Further, understanding the linkages back and forth encourages people to look at systems from an ecosystem approach prior to making changes. The assessment of trade-offs, what you gain by changing the landscape/adding a species compared to what the larger costs are, is essential to balance biodiversity and ecosystem function with the services we want to get from ecosystems.

3 Responses to “Biodiversity Loss and Cascading Effects”

  1. Culture Kid says:

    I find this an interesting post because it once again brings up questions of scale – this time, the proper scale for an ecological study. We’ve had many, many discussions regarding this contentious topic throughout our class, and this post demonstrates the fact that perhaps until recently, we only attributed the complications of scale to research involving humans – that is. And while the problems and ramifications of introduced species are indeed associated with humans, the chains of causality are more indirect than, for example, Line Gordon’s discussion of interruptions to global water systems from agriculture. Thus where does an ecosystem – directly or indirectly anthropogenic – begin and end? This question is becoming ever more central in an era of globalizing modernity and consequent environmental degradation.

  2. merle says:

    I want to take up this important question about the limits or frontiers separating (and also constituting) two adjacent ”beings”, where ”being” must be taken here in a very broad sense to refer to any unitary entity we might want to refer to. I think we must realize that the problem of determining where one ”being” ends and another begins does not arise only when we try to determine the exact line separating two ecosystems. It also arises if I try to determine with precision where my body ends and another begins, where my body ends and my environment begins, where an electromagnetic field ends and another begins, and so forth. This problem arises everywhere because we are responsible for dividing up the world as we do. It does not have to entail that our distinctions are arbitrary, but I will not go into this highly technical debate. For our purpose, I think it would be helpful first to realize that all disciplines have to face this problem and second to inquire at how they manage to deal with it.

  3. Jones says:

    I have a particular idea about this topic that intrigues me, but I have no way of exploring it, other than through speculation.
    As has been noted, the introduction of an invasive (another term that probably has its roots in a social construction of nature) can greatly disrupt the dominant relationships in an ecosystem, with unforeseen consequences reverberating throughout the whole of the system. But, on the other hand, a disrupted ecosystem provides opportunities for evolutionary adaptations to take place; evolution is dependent on a changing environment. Ecosystems and their organisms can experience rapid evolutionary change after the introduction of an alien species, since the new species can open up previously unavailable niches. Perhaps as we destroy ecosystems, and place a number of species at risk of extinction, we are also facilitating an outburst of adaptive evolution and creation that would otherwise not occur. Just as we can’t predict what will be lost when an alien species is introduced, we can’t predict what will be gained, if anything.