How animal “social networks” shape ecosystems
New research shows that cross-species social networks can determine how entire populations of wild animals grow and respond to environmental change, impacting the health of ecosystems.
We live in an age when social media connects human beings in profound ways, allowing individual actions to spread like wildfire and drive real change to our social, political and economic systems. But can the social networks of animals possess similar world-changing power? New research, led by my colleagues and I at the University of California, indicates that the answer is yes — and that understanding animal social networks is critical to conserving precious natural resources.
Why? It turns out that profound ecological consequences can emerge from simple copying behavior. When an individual needs something, it’s often very useful to observe and copy the behaviors of others who share that need. For example, if you’re looking for a good place to grab a bite, following crowds of other hungry people is a great way to find a reliable eatery. Similarly, if you’re a vulture looking for carcasses distributed randomly across a landscape, it makes sense to descend from the skies when you see other vultures descending, too.
These shared needs aren’t restricted to food: if you’re a zebra that wants to avoid getting eaten by a lion, and you see zebras and other lion prey fleeing for their lives, it’s probably wise to follow suit!
This may seem obvious; copying the behavior of others to meet one’s needs is a ubiquitous phenomenon in the human world and in nature. But what we are newly discovering is that when wild animals copy one another, it can determine how their populations and communities grow, function and respond to environmental change — and, ultimately, whether or not they will go extinct.
For example, take tropical coral reefs, a hyper-charismatic ecosystem. Coral reefs are not only unparalleled bastions for biodiversity, but they support the lives and livelihoods of hundreds of millions of people globally, through such industries as fisheries and tourism. My colleagues and I have an ongoing study on the social networks of mixed-species assemblages of coral reef fishes. In particular, we study large herbivorous fishes like parrotfish, tangs and rabbitfish, which perform a critical service to the ecosystem: they eat algae that, if left unchecked, can kill corals and destroy entire coral reefs.
Using some very unorthodox approaches involving massive underwater video camera stands, we have shown that, by simply paying attention to and following the movements of one another, the fish community is able to greatly increase how much algae it can consume. This is because fish not only follow one another into and out of dangerous feeding grounds where hungry sharks lurk, but when they’re surrounded by more fish, they stay in these feeding grounds for longer periods, eating more algae. Our findings indicate that by showing each other when to enter, stay in or leave dangerous feeding grounds, reef fish — even when they’re from different species — can help each other perform their ecologically critical function as well as survive.
This kind of pattern is not limited to coral reefs: in various ecosystems, the higher the number of similar animals in an area, the more potential opportunities for each individual to copy valuable behaviors — assuming there are enough resources to go around. This can cause what ecologists refer to as “positive density dependence”: a positive relationship between the density of a species in a habitat and the rate at which its entire population grows. This may sound like a good thing, but for species that are struggling, it could spell disaster.
The implication is that when humans reduce the numbers of wild animals by fishing, hunting, pollution or destruction of habitat, we’re not just losing individuals and species, but the loss may disrupt the animal social networks they belong to and endanger the critical ecological services these support, as in the example of fish removing harmful algae from coral reefs. Furthermore, by reducing animal populations, we may make these populations more susceptible to extinction through a dangerous feedback loop, in which loss of individuals and the information they provide to their social network reduces survival and reproduction for remaining individuals, leading to fewer individuals, and so on.
Gaining a better understanding of animal social networks — rigorously quantifying what may seem intuitive — should help us do a better job of figuring out improved approaches to ecosystem conservation and natural resource management. It’s a timely quest, especially given global efforts to improve food security and sustainability as the human population rises.
This is still only the beginning of the learning process. Moving forward, my team and I are beginning to harness the power of new technologies — including artificial intelligence — to collect and analyze big data from nature. Using this, we’ll build models that sharpen our understanding of how simple social behaviors can scale up to affect the natural world and, consequently, the human world.
For more of my research, as it unfolds, follow SciAll.org.
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