Last month, new research was published in the journal PLoS ONE detailing a greater than 70% decline in flying insect biomass in protected areas in Germany. Even more concerning, these declines occurred in just under three decades. To identify biomass declines, the authors sampled flying insect communities in 63 protected sites over a 27-year period using malaise traps (essentially a large tent-like net that traps flying insects). Samples were collected across a habitat gradient, and the authors took into account various landscape and environmental variables that could potentially impact flying insect biomass. Their overall conclusion was that a dramatic decline in biomass has occurred at these sites and that this decline cannot be easily explained by the landscape, temporal, or climatic factors that were included in their analyses. It is currently unclear exactly what is driving this decline in insect biomass, but large-scale factors that act across multiple habitat types and impact communities even in protected landscapes are likely to blame.
These new findings add to a growing list of research documenting declines in a wide variety of invertebrate groups from ecosystems around the globe. For example, freshwater mussels have experienced severe population declines in many species and exhibit extremely high rates of endangerment. In some groups of invertebrates, population declines have been well documented, especially for groups like bees and butterflies that have economic importance or are colorful and widely observed. However, invertebrate population declines are generally less discussed than their vertebrate counterparts, despite the fundamental role that invertebrates play in ecosystem function and the severe negative impacts that these declines could have on other groups.
It is difficult to fully state the number of ways that invertebrates contribute to healthy ecosystems. Invertebrates far outnumber vertebrates in both diversity and biomass and most if not all ecosystems could not function without them. They perform a wide variety of ecosystem services, ranging from pollination to nutrient cycling to serving as an important food source for higher trophic levels. Along with amphibians, many species of invertebrates serve as links between aquatic and terrestrial ecosystems via yearly breeding events, which move nutrients and biomass between different environments. Invertebrates form the base of many food webs and are particularly important sources of food for many amphibians and reptiles. For example, larval flatwoods salamanders eat mostly small crustaceans, and hellbenders feed primarily on crayfish. Some invertebrates also act as important and efficient predators, particularly in fishless aquatic environments where tadpoles will alter their behavior to reduce their risks from an invertebrate predator. These many and complex ecosystem services make the preservation of diverse and abundant invertebrate communities an important goal that is often neglected in favor of more charismatic species.
In addition to the importance of invertebrates, this research also highlights a major conservation issue – the continued decline of certain species or groups in protected areas. Europe and the southeastern U.S. are actually very similar when it comes to protected areas. Both tend to conserve land as islands surrounded by an ocean of altered and degraded habitats. Dense road networks and unsuitable habitat patches make it difficult for many species to move and disperse effectively, decreasing gene flow. Conversely, other species, especially birds and flying insects, are capable of easily moving to habitats outside of protected areas, which may increase mortality risks. Furthermore, many factors (e.g., climate change, pollution, or disease) leading to population declines can impact species even when they occur completely on protected lands. Some severe amphibian declines caused by the Chytrid fungus occurred in populations that were otherwise protected.
Population declines on protected landscapes highlight the importance of population monitoring, not just for rare species, but also for common species that perform important ecosystem functions. Early warnings of declines are crucial to identifying problems and finding solutions. Finally, it also reinforces the importance of effective management on land set aside for conservation. Without good management that promotes healthy ecosystems, environments will continue to degrade regardless of whether or not they are protected.