Arctic Warming and the Atlantic-Pacific Fish Interchange

by Kyle Jensen

For most of the Quaternary Period the inhospitable environment north of the Arctic Circle has served as a biotic barrier between Northern portions of the Atlantic and Pacific oceans. Through it is known that interchange across the Northwest and Northeast passages has occurred, currently only 135 of over 800 fish species found above 50° of latitude are found in both oceans. Continued warming may result in the reopening of these passages resulting an accelerated interchange of species between the Atlantic and Pacific as species follow favorable conditions into higher latitudes. This may also lead to increased movement of fishing and shipping vessels through these channels, which could facilitate further interchange. This has the potential to impact the food webs and biodiversity of systems in both of these oceans, the consequences of which would affect ecosystems currently comprising 39% of global marine fish landings. To analyze potential impacts of future species interchange, Wisz et al (2015) has made forecasts of potential distributions for 515 fish species. Continue reading

Are species distribution models validated by field trials?

by Kyle Jensen

Invasive species, especially plant species, are one of the greatest current threats to the Earth’s biodiversity. It is feared that with the advent of global warming areas favorable to such species will increase, especially for those invasives from warmer climates that have naturalized near areas of marginal temperature. This could have negative impacts on the diversity of exposed populations, so species distribution models (SDMs) have been developed to estimate possible future distributions of organisms. These models make predictions by relating occurrence data to environmental conditions, giving a general idea of how the potential threat of an invasive species may change over time, and suggesting possible mitigation activities. Such models however have rarely been tested against experiments from the field. Sheppard et al. (2014) seek to validate SDMs through field trials at varying sites based on suitability as predicted by SDMs. If the predicted success of species in the models matches those of actual field trials, then we could be more confident in ability of models to assess the risk of invasive success. The experiment also addresses the validity of the enemy release hypothesis, which is often assumed to be the case in invasive studies. The hypothesis posits that invasive species leave behind any natural enemies when they are introduced to a new environment, which would contribute to their success. This experiment questions that assumption and its use in SDMs. Continue reading

Hierarchical Responses of Plant-Soil Interactions to Climate Change

by Makari Krause

Ecosystems provide a multitude of services to humans, but one that will continue to grow in importance as climate change progresses is terrestrial carbon storage. In their paper, Bardgett et al. (2013) develop a framework for understanding the multiple mechanisms through which climate indirectly impacts the carbon cycle. These mechanisms are broken into three categories: individual responses, community reordering, and species immigration and loss. Individual responses only include changes to individual organisms without any alteration of the larger communities in which they live. While the individual responses occur in the short term, in the long term (years to decades) observable changes will occur within entire communities. This community reordering involves changes in the abundance of certain species but not the complete extinction of species or the invasion of new species. If the time period is extended even further there will be shifts in species resulting in the invasion of new species and the extinction of old ones. Each of these responses alters interactions between soil and plant communities and has associated implications for the global carbon cycle. Continue reading