Trade routes and the evolution of transportation technology have increased the frequency and magnitude of non-native species invasions. The geographical isolation of species has been eroded by human travel and climate change has been found to increase habitat availability for non-native species. Invasions can have negative consequences for native species, ecosystem functioning, and the economy. In this essay, I discuss few examples in literature and suggestions of how ecological hypotheses could be addressed under the novel ecosystems framework, as it pertains to trade routes and movement of species.
Globalization is “the process in which people, ideas and goods spread throughout the world,
spurring more interaction and integration between the world’s cultures, governments and economies” (Globalization, n.d.). From an ecological perspective, the spread of goods and integration between economies also facilitates the release of non-native species, due to transport vectors and pathways increasing in number and frequency of use. Advances in navigation technology also mean that the speed and the scale of species movement will continue to increase (Figure 1).This creates an interesting phenomenon not only for biologists studying communities and their resilience, but also throws in a challenge for public policy and management of species.
Humans are removing barriers of dispersal for species. Now, non-native species have challenged expectations under various theoretical frameworks in population biology, population genetics, and ecology. For example, in island biogeography theory, distance to suitable habitat is a key predictor of species richness, however, in today’s world distance alone might not tell us much about the capacity of an area to carry certain number of species (Figure 2). When dispersal barriers are removed, we need to look at climate similarity (niche suitability) and transport vectors (propagule pressure) to better predict the success of a species in colonizing a new area. Capinha and colleagues (2015) empirically tested how a break in biogeographic boundaries via human transport makes climate and trade relationships the best variables to explain species distributions. Thus suggesting that climate and perhaps socioeconomic relationships will define the new biogeography of the Anthropocene. Other researchers are also drawing the same conclusions, such as Helmus et. al. (2014) in their study about Anolis lizard diversity among Caribbean islands. They concluded that the amount of economic trade via shipping was a better predictor of species diversity than geographic isolation alone.
Figure 2. (a) The linearization of the Caribbean anole species–area relationship (SAR) and (b) the flattening of the species–isolation relationship (SIR) after considering transport pathways. In this figure, blue-colored lines represent expectation under classic island biogeography, whereas red-colored lines was the trend found by Helmus et. al. 2014. The number of species used to be dominated by colonization and speciation, respectively. However, when considering modern shipping, colonization became the major force on all islands. Edited from: Helmus, M.R., Mahler, D.L., Losos, J.B. (2014). Island biogeography of the Antrhopocene. Nature, 513, 543-546
Erle Ellis, an American environmental scientist and member of the Anthropocene Working Group, lamented in an interview that ecologists are resistant to include human factors into ecological models (Singer 2014). Ambivalence continues around the idea of including human agency either as a component of novelty or as requirement for our studies on novelty going forth, perhaps since human influence is so prevalent.
Humans have been reshaping the Earth since the Late Pleistocene, altering the landscape, domesticating certain species and even expanding species ranges, and so it seems daunting to account for human influence in models. However, we are living in a time where our own technological advances provide us with powerful tools to study how our societies drive climatic and biogeographic patterns. We can now get detailed information from current and past legacies (stable isotopes, ancient and mtDNA, remote sensing, etc.) to quantify the extent and intensity of anthropogenic alterations and its effects on biodiversity. As evidenced in a paper on the anthropogenic shaping of global species distributions, Bovin et. al. 2016 used multiple molecular, computational and archeological evidence to show how human transformations have created novel ecosystems around the world. His group provided evidence that the changes in ecosystems and spread of non-native species were and still are primarily mediated by human migrations and their economies.
Non-native species transport and human agency are so intertwined that the way in which our economies work could dictate how many species – and at what rate- will assemble in a given area. This might mean that as more countries become active in the global trade network, inevitably, the risk of introducing species will increase. Further, the number of trade routes and number of visits can increase propagule pressure (introduction effort, or the number of individuals introduced to into a region) which is a key element of invasive species persistence.
A great opportunity for research given this situation is the study of novelty from the biotic perspective. One example might be by contributing to the body of research under the biotic resistance hypothesis, which states that diverse biotic communities are more resistant to an invasion. This hypothesis was based on Sir Elton’s work on how the combination of predation, competition, and aggression can act as a barrier to invasive species establishment and abundance. Nevertheless, there is still a lack of understanding on the mechanisms underlying the variation in susceptibility of biotic communities to species invasion. Under the novel ecosystem framework, we might be able treat trade routes as a source of biotic novelty. As a first step, we can identify older trade routes versus newer ones, quantify the number of native and nonnative species present and compare the species richness, evenness and function in each region at different scales from a port. A significant difference in these numbers can allow us to test hypothesis about biotic resistance to invasion. Further, by looking at differences in species function between two regions differing in number of trade routes and usage, we might be able to assess how trade routes can also serve as an agent of biotic homogenization.
Boivin, N. L., Zeder, M. A., Fuller, D. Q., Crowther, A., Larson, G., Erlandson, J. M., … Petraglia, M. D.(2016). Ecological consequences of human niche construction: Examining long-termanthropogenic shaping of global species distributions. Proceedings of the National Academy ofSciences , 113(23), 6388–6396. http://doi.org/10.1073/pnas.1525200113
Capinha, C., Essl, F., Seebens, H., Moser, D., & Pereira, H. M. (2015). The dispersal of alien speciesredefines biogeography in the Anthropocene. Science, 348(6240), 1248–1251.http://doi.org/10.1126/science.aaa8913
Globalization. (n.d.). Retrieved December 13, 2016, from https://www.merriam-webster.com/dictionary/globalization
Helmus, M.R., Mahler, D.L., Losos, J.B. (2014). Island biogeography of the Antrhopocene. Nature,513, 543-546. http://doi.org/10.1038/nature13739
Singer, E. (2014, October). Lizard stowaways revise principle of Ecology. Scientific American. Retreived from http://www.scientificamercian.com/article/lizard-stowaways-revise-principle-of-ecology
Ecóloga, Mujer y Puertorriqueña. Sarcástica, pero seria