Many species globally are threatened by numerous biotic and abiotic stressors, resulting in declining population and shifts in ecosystem functioning.

Science recently released a special issue on defaunation, which spanned seven articles detailing the recent decline in animal species diversity and abundance.  Among others, the issue included two peer-reviewed articles, an opinion piece, and an analysis of national policies tied to global and local conservation strategies.  The statistics associated with defaunation are sobering, but the issue presents a few solutions to help us curb this global environmental crisis.

First, a damage assessment.  According to Defaunation in the Anthropocene, between 11,000 and 58,000 species go extinct each year.  At least 16% of all vertebrate species are endangered or threatened, and there’s been a 28% decline in their abundances since the 1970s.  Approximately 40% of invertebrate species are considered threatened, though less than 1% of described invertebrates have been assessed.  There is data to suggest that invertebrate species’ abundances are also decreasing, but it’s difficult to put an exact number on that decline since they are not as well monitored as vertebrates.  On a global scale, these statistics may be underestimated because our monitoring practices bias our data toward specific taxa.  Groups of large and charismatic organisms, like mammals and birds, get most of the attention because they are easier to monitor and more sympathetic than invertebrates, amphibians, and reptiles.  In some systems this is beneficial, where large mammals and birds are the most threatened and contribute significantly greater function to an ecosystem than smaller organisms.  However the opposite can be true in other instances, so it is critical that we prioritize greater sampling of underrepresented groups.

Additionally, there is concern that such measures of declines in species and abundance may not reflect the true extent of our ecological troubles.  Shifts in ecosystem compositions may not be reflected in a given measurement of biodiversity, yet are nonetheless indicative of environmental change.  The primary goal behind many conservation strategies has been to restore a species or population to a certain number.  While population viability is critical for any species, the authors argue that ecosystem functionality is a useful yet underutilized goal for conservationists.  With this goal, the composition of an ecosystem (i.e. the identity and abundance of resident species) can be more flexible, as long as the ecosystem functions in a similar way.  The issue with this then becomes how to measure ecosystem function, or rather, against what do we compare it?  Do we set an arbitrary time in history that we would like to restore it to, or do we attempt to maintain its function while integrated with a unique environment managed by humans?  Some proponents of the latter strategy see historical comparisons as unrealistic and uninformative, especially given our changing climate.  Regardless, restoring the functionality of ecosystems is a key predictor of the future success of not only animal and plant populations, but the human population as well.

One of the strongest arguments this issue makes derives from its use of specific economic values of animals and ecosystems.  According to the article Wildlife decline and social conflict, the harvest of land and sea animals accounts for $400 billion annually around the world.  Defaunation in the Anthropocene claims that pest control by native U.S. predators is worth approximately $4.5 billion annually, and that the decline in North American bat populations (a specific type of pest controller) has cost the agriculture industry $22 billion in lost productivity.  Insect pollinators are required for about 75% of the world’s food crops, and are therefore responsible for approximately 10% of the economic value of the entire world’s food supply.  According to the World Bank, food and agriculture represents about 10% of global GDP, which in 2012 was estimated at $72 trillion.  If we take total food supply to be approximately $7.2 trillion (again, estimating), then insect pollinators are worth around $72 billion dollars.  These estimates apply tangible figures to a broad and occasionally overwhelming issue, and may be good starting points to unite many different stakeholders under a common currency.

The article Reversing defaunation: Restoring species in a changing world details the different strategies conservationists use to preserve species abundances and their associated ecosystem functions.  These strategies can broadly be grouped into two categories, translocations and introductions.  Translocations involve moving individuals within their indigenous range to either reinforce a local population or to reintroduce them following a local extinction.  Introductions, on the other hand, move species outside of their indigenous range to prevent a global extinction of a species or to replace a lost ecosystem function.  Though planning a conservation strategy in terms of these labels can be useful for setting long-term goals, they are not mutually exclusive.  Certain strategies can incorporate aspects of both translocation and introduction, or can introduce a species both to preserve its numbers and to restore ecosystem functionality.  Therefore, it’s best to use these terms as guidelines for how to measure the success of any plan rather than as constraining requirements.

These losses in biodiversity, and their associated shifts in ecosystem functioning, are primarily driven by a combination of over-hunting, habitat destruction, impacts of invasive species, climate change, and disease.  The Defaunation articles make a point of addressing national policies aimed at preventing species extinctions, namely those regarding over-hunting and poaching.  Many of these policies simply impose penalties for illegal hunting rather than address the underlying causes of the issue, poverty and starvation.  While it’s unrealistic to expect a conservation plan to alleviate world hunger and income inequality, it may be useful to consider animal overexploitation as an unintended side-effect of the economic cycle caused by scarcity.  Supply and demand states that as a species becomes less common, its value on the market rises.  However, this scarcity also leads to a reduction in the amount caught per unit effort.  The rise in price drives a greater hunting effort by the sellers, further decreasing the population, and the cycle begins again.  Since many of these hunters are using their profits to feed themselves or their families, simply enacting penalties for poaching may not have the intended effect.  Overhunting is not a simple problem, and most likely will not have a simple solution.  However, the only way we can begin to address it is by determining its causes.

September 30, 2014