How does fragmentation affect biodiversity? A controversial question at the core of conservation biology

By Richard B. Primack, Abraham J. Miller-Rushing, Vincent Devictor

“A [tree] which it has taken two centuries to perfect, rising by slow stages into the heavens, has this afternoon ceased to exist… Why does not the village bell sound a knell? … The squirrel has leaped to another tree; the hawk has circled further off, and has now settled upon a new eyrie, but the woodman is preparing [to] lay his axe at the root of that also.”  Thoreau in his Journal. 

Does fragmentation harm biodiversity? For many years, most conservation biologists have understood the answer to be “yes.” It seems obvious—fragmentation divides landscapes into smaller patches that support fewer species. Edge effects further erode the ability of small patches to support many species. The negative effects of fragmentation are taught to students in introductory biology, ecology, and conservation courses, and affect conservation strategies and management. 

Forest Fragment in Costa Rica.

However, as we describe in a recent editorial, Fahrig and co-authors recently argued that the evidence base for these ideas, recommendations, and actions is not as strong as many think, largely due to the confounding effects of scale, habitat amount, and fragmentation. Their analysis even suggests that in many cases fragmentation might enhance biodiversity. Other conservation biologists have strongly disagreed with these findings, arguing that habitat fragmentation does harm biodiversity.

Getting the answer right in this debate is critical because it allows us to (1) understand the consequences of roads, development, and other fragmentation-inducing human actions on biodiversity; and (2) prioritize the protection and management of lands in cases when deciding between protecting large intact landscapes or fragmented landscapes with the same total amount of habitat. 

This debate highlights the need to make sure we continue to investigate questions central to conservation and check the evidence supporting our understanding and decisions. We think this process is healthy for the field, especially if we can keep dialogues productive and respectful. 

Key papers in the debate are linked below:

Fahrig, L. (2017). Ecological responses to habitat fragmentation.

Fahrig, L. et al. (2019). Is habitat fragmentation bad for biodiversity?

Fletcher Jr, R. J. et al. (2018). Is habitat fragmentation good for biodiversity?

Investigating ecological mismatches with citizen science

Posted by Abraham J. Miller-Rushing, Amanda S. Gallinat, and Richard B. Primack 

“I had three chairs in my house; one for solitude, two for friendship, three for society.” 

-Henry David Thoreau, Walden 

It’s tough to study how climate change disrupts interactions among species. Many interactions, like those between predators and prey, are typically hidden from view. However, creative use of citizen science can provide insight into these hidden interactions. In a recent article in the Proceedings of the National Academy of Sciences, researchers used online and virtual reality games played by volunteers and analyses of long-term citizen science field observations to explore changes in relationships between stinging bees and wasps, stingless hoverflies that mimic bees and wasps, and bird predators that like to eat hoverflies but avoid bees and wasps.

Fig. 1. In one online game, Hassall et al. used citizen scientists to identify the visual similarity between hymenopteran model (right) and syrphid mimic (left) pairs.

These scientists found that a warming climate is changing the relationships among the stinging bees and wasps, mimic hoverflies, and bird predators, likely to the benefit of bees, wasps, and birds.

Follow the links below for the paper by Hassall et al. and our associated commentary.

Hassall et al. 2018. Climate-induced phenological shifts in a Batesian mimicry complex. PNAS

Miller-Rushing et al. 2018. Creative citizen science illuminates complex ecological responses to climate change. PNAS

Opening our eyes to the world

Posted by Richard B. Primack

“The true harvest of my life is intangible - a little star dust caught,

a portion of the rainbow I have clutched.” 

Henry David Thoreau

Wonderous things are all around us if we only keep our eyes open. 

On October 24, as the Red Sox were about to play the Dodgers in Game 2 of the World Series, an incredible full rainbow stretched across the eastern sky, illuminated by the setting sun, linking together Boston University buildings. And the Red Sox won the game!

During a late autumn walk through the Hammond Woods in Newton, I observed an amazing hanging rock. This puddingstone rock is 2 ½ to 3 feet on a side, and probably weighs around 3,000 pounds. The rock has been suspended between these two rock faces for at least 12,000 years, but this was the first time I had noticed it in many decades of walks through the woods. 

The lives of Boston residents were enriched this year by Fog X Flo installations throughout the Emerald Necklace.  At set times, spray nozzles generated large fog banks, creating unique visual and atmospheric effects as they drifted across the landscape.  

Let’s resolve to be more awake to the world around us in 2019!