Last Week of the Semester: Human Ecology, Reflections, and Process

Chapter 12: Human Ecology

            In this chapter Jim touches upon an issue which has always bugged me: the exclusion of humans as a part of ecosystems. I’ve been somewhat perplexed by the distinction that is traditionally made between what is “artificial”, i.e. human, and what is “natural”, i.e. everything else. There is no arguing that humans have a very unique ecology relative to other animals (even within primates), but we evolved by the same natural processes that other organisms do, and we are subject to the same types of ecological constraints (even if we are somewhat off the charts relative to everything else).

            Human ecology is a very interesting but poorly understood topic (at least at the time this book was published). This chapter places humans into two interesting contexts. The first context is as the keystone species of the ecosystems that we so significantly shape. The other context is that of an invasive species, our role in introducing other invasive species, and our negative impact on the rest of earth’s biota. I will focus on this latter topic briefly and leave everything else for class discussion.

            Given that the patterns we see with regards to fragmentation of populations of endemic species and the degradation of habitat make absolutely no sense except in the light of human activities, isn’t it counter intuitive to treat humans as separate from nature? There is also the issue of whether or not introduced species should unilaterally be considered bad. The chapter cites some examples of unique ecosystems where invasives have increased local diversity. I find the example from page 220 particularly intriguing: here you have a dam that was constructed (a human activity) which creates an environment that endemic species are not adapted to, but which invasives can be successful in. If you MUST have the dam, which is better: an ecosystem with no fish, or a new ecosystem consisting of introduced species? In fact, Jim presents a fairly long list of instances where invasive ecosystems are not entirely bad. That’s not to say they are always good, there are just as many examples of invasive species causing the demise of important keystone endemics. Once again, I think using a macroecological approach and looking at the bigger picture is beneficial.

            After reading this chapter I asked myself, what is the human niche? I don’t think I can even begin to answer that question.

Chapter 13: Reflections and Process

            I’m not going to say much, other than Jim encourages us to go out and use the macroecological approach to study the systems we find interesting. The three areas he cites as having especially large opportunities are the identification and characterization of statistical patterns, evaluating hypotheses, and interdisciplinary collaboration. 

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John Alroy’s 2001 Paper: A multispecies overkill simulation of the end-Pleistocene megafaunal mass extinction

            While I could dispute whether or not the end Pleistocene extinction was a “mass” extinction, I thought it was a fun paper and I liked it very much. He presents the results from a mechanistic model which invariably predicts the demise of North American megafauna. This model incorporates parameters and causal mechanisms from the published literature; these are listed in the first full paragraph of the second column of the first page.

            The model can more or less predict which organisms go extinct (with a couple exceptions) and does a fair job at estimating the timing of extinctions. The result is the same without invoking climate change or preferential hunting of large animals. In summary, humans didn’t have to go out killing every last large animal on the continent to cause an extinction. The model suggests that humans would have to preferentially prey upon small animals to prevent the extinction from occurring.

            There are two really important items I want to highlight. First, John’s paper invokes human ecology in addition to that of megafauna to characterize the extinction. That’s why I thought it was such an appropriate choice for this week. Second, I think this paper does a good job of highlighting the mechanisms that can send organisms into an extinction spiral. His model doesn’t even include the compounding effects humans likely had on Pleistocene ecosystems: disease, burning, modification of landscapes, to name a few. These are some things I think we can spend some time talking about during the discussion. I’d also like to hear what people thought about the model, and the data that went into it. There is a long (very long) SI that goes with the paper, which I fully admit I won’t have a chance to look at before class tomorrow. If anyone else can chime in on that, that would be awesome.