Over the past 30 years, leading scientists in ecology and conservation biology have been claiming a biodiversity crisis, and have documented global extinctions of birds and mammals occurring at rates that greatly exceed pre-industrial times. The dominant narrative is one that claims biodiversity is in decline, and that ecosystem services depend on biodiversity (many of such services are enjoyed by humans).
A study by Worm et al. 2006 found positive relationships between diversity and ecosystem functions and services. Specifically, they found that “the societal consequences of an ongoing erosion of diversity appears to be accelerating on a global scale”, and that this trend “projects the global collapse of all taxa currently fished by the mid–21st century.” In fact, the only marine fish documented to have gone extinct is the Galapagos Damsel, believed to have never recovered from a temporary increase in local water temperatures during the El Niño–Southern Oscillation of 1982 and 1983 that caused their prey source, plankton, to decrease dramatically.
As it turns out, the story is not quite so simple. A recently published book titled ‘Effective Conservation Science: Data not Dogma’ contains a chapter titled ‘Are local losses of biodiversity causing degraded ecosystem function?’ authored by Dr. Mark Vellend, a professor at Universite de Sherbrooke. In this chapter, Dr. Vellend addresses this “biodiversity crisis”, pointing out that the arguments about biodiversity decline was intact up until about 15 years ago, when Sax et al. 2003 showed that fewer species globally does not imply fewer species regionally or locally. Specifically, the number of non-native species established either matched or greatly exceeded the number of recently extinct species, within regions.
Their findings demonstrated a dramatic increase in species richness of plants and fishes on oceanic islands since the arrival of humans within the past few thousand years. They also found increases in richness within continental regions since the arrival of Europeans within the past few centuries (see Figure 1). The most striking result showed that colonizations of islands by plants have “outnumbered extinctions to such an extent that a typical oceanic archipelago is now home to roughly twice as many plant species than were present prior to the onset of intense human occupation. These results” Vellend wrote, “run strongly counter to the biodiversity-crisis narrative.”
These conflicting arguments demonstrate that long-term changes in species richness have been the subject of recent debate. Specifically, global richness is declining, but it is unclear whether sub-global trends differ. The question remains: do global and sub-global time series have opposing trends? A recent study by Batt et al. 2017 addressed this knowledge gap by testing for multi-decadal trends in marine species richness around North America. Their results supported the conclusion that regional richness trends are generally positive around the world and across ecosystems. Specifically, they found long-term trends in regional species richness were positive in nine open marine ecosystems, meaning the average number of different species found in these regions from 1970-2010 has increased (see Figure 2). Further, their findings “suggest that the spatial dynamics of individual species are closely tied to richness dynamics, which might explain differences between local, regional, and global trends.”
While the evidence does appear to be mounting in support of species richness increasing in individual ecosystems, acceptance of reports perceived to be against the dominant narrative may be limited. That is, any report that does not claim biodiversity as being in decline may not be as well-received and as likely to be published as their doomsday counterparts. In the book ‘Effective Conservation Science: Data not Dogma’, Dr. Vellend wrote about warnings he received about the political dangers of reporting results from a study he and his colleagues had carried out that contradicted the assumption that local-scale plant biodiversity loss is widespread. Similar studies have also been criticized for their potential political implications. “A worrisome implication of this sentiment is that the burden of proof might not be equal from study to study, but rather depends on how the results align with conventional wisdom or political priorities,” wrote Dr. Vellend. “If a given study finds evidence that supports the value of biodiversity conservation, can we hold such studies to a lower standard of “demonstrating results beyond a reasonable doubt”? Should we preferentially promote the publication of such studies in high-profile journals so that the public can reach the conclusions we would prefer them to reach?”
This highlights an important point about walking the fine line between scientific objectivity and political advocacy. Should we avoid publishing results that go against the status quo for fear that media reporting will misinterpret results? No, we should not. Instead, the former should be valued over the latter, and publications should be held to the same high standards regardless of whether or not they support popular political positions. While it is true that some media reporting tends to skim over results and highlight false or misleading results, this should not encourage the scientific community to publish “preferential” results only, and they should unite in an effort to clear up any misleading reporting. This, after all, is the key reason the website on which you are currently reading this article exists.
Rather than being viewed as findings that go against the status quo, evidence demonstrating biodiversity stasis over time at local and regional scales will hopefully be viewed as an added data point that will help us to improve our understanding of ecosystem trends and drivers and assist in better predicting and managing changes in biodiversity.