Roca Partida, part of Mexico’s Revillagigedo Archipelago, does not sound like much real estate. It is an isolated volcanic pinnacle surrounded by thousands of kilometres of open ocean, with steep walls dropping to around 263 feet (80 meters). It’s only about 328 ft (100 m) long, too, yet this tiny patch of rock attracts an impressive cast of predators, including four species of sharks.

One would think in such a tiny space, food and… well, space, are limited. So how can so many large predators spend time in such a small place without constantly competing with one another? One possibility is that they simply do not use the habitat in exactly the same way. Ecologists call this “resource partitioning;” essentially, instead of competing for precisely the same resources, species divide them up. One animal might feed on different prey, another might forage at a different time of day and another might occupy a different part of the habitat. In the ocean, where a three-dimensional world offers animals opportunities to move above and below one another, depth can become an important part of that equation. Researchers recently used acoustic and satellite telemetry alongside ecological niche modelling to investigate how four shark species use the vertical space around Roca Partida : Galapagos ( Carcharhinus galapagensis ), silky ( Carcharhinus falciformis ), silvertip ( Carcharhinus albimarginatus ), and whitetip reef sharks ( Triaenodon obesus ).

The results revealed some pretty striking differences! Galapagos and silky sharks generally stayed relatively shallow — their vertical niches were narrow, with the highest probability of occurrence around 82 ft (25 m) and very little use of depths below 164 ft (50 m). Silvertip and whitetip reef sharks, by comparison, used a broader range of depths and were more likely to occur deeper in the water column, with peak probabilities around 164 ft (50 m) for silvertips and 131 ft (40 m) for whitetip reef sharks. Of course, that means there was some overlap (particularly around 82 to 155 ft/25 to 35 m), but overall, the sharks were not simply swimming randomly throughout the water column. For example, silvertip sharks were significantly separated from that of the other species; some individuals spent much of their time between roughly 66 and 164 ft (20 and 50 m), while another spent most of its time much deeper, around 263 to 328 ft (80 to 100 m). But the researchers found considerable differences within species, too. Two whitetip reef sharks, for example, could use dramatically different portions of the water column: one might spend much of its time shallower than 66 ft (20 m) while another rarely ventured above that depth. Among silvertips, some individuals favoured relatively shallow waters while another repeatedly occupied much deeper habitat. Timing may also be another way to avoid competition. Galapagos sharks were detected predominantly at night while silky sharks appeared more often during the day, suggesting these species may partition the pinnacle not only vertically but temporally.

Think of it like a group of people sharing a house, except the house is Roca Partida. From the outside, the household uses the entire building. But inside, one person might spend almost all their time in the kitchen, another in the backyard and someone else claims the quietest bedroom with the nice bay window overlooking… well, in this case, water, but you get the idea. The overall space is broad, but each individual’s personal footprint is much smaller!

There is an important caveat, however. The sharks were not all tagged during the same periods, so differences between species could potentially reflect changes in environmental conditions rather than deliberate avoidance. Because of this, the researchers say the study cannot demonstrate that competition is definitely causing the observed patterns. Temperature could be one explanation to all of this; sharks often adjust their swimming depths in response to changing temperatures, and water temperature can affect metabolism and other physiological processes. But temperature alone did not seem to explain the patterns at Roca Partida, since the sharks generally encountered similar surface temperatures, while some individuals experienced surprisingly different temperatures at depth.

Prey distribution could be important here, then. Roca Partida is an unusually productive oasis in an otherwise nutrient-poor pelagic environment, supporting high concentrations of fishes. The pinnacle’s walls and crevices also offer potential feeding opportunities. Whitetip reef sharks have an advantage that the other species may lack (i.e., they can rest and maneuver close to the structure and extract prey from crevices). Then there is competition itself. Game theory models of habitat selection predict that animals can respond to both the availability of habitat and the presence of competitors. A species that is abundant may behave more like a habitat generalist while a less abundant species may specialize in particular habitat types. At Roca Partida, the abundant whitetip reef sharks broadly fit that prediction, whereas the silky and Galapagos sharks appeared more specialized, particularly toward shallower water. Silvertips, however, did not fit the prediction quite as neatly. Their vertical niche was broad despite their relatively low abundance.

Rarely does nature allow its animals to fit in the little neat boxes we create for them.

We still need to know what the sharks are actually doing in those different depths. Are they following particular prey? Avoiding competitors? Seeking specific temperatures? Conserving energy? Or are several of these forces operating simultaneously? The team of scientists say that future studies using stable isotopes, fecal DNA, accelerometers and animal-borne cameras could help connect where sharks swim with what they eat and how they behave while they are there. For now, Roca Partida offers a useful lesson in the complexity of coexistence: a habitat does not have to be large to support a diverse community. It’s fascinating how the many different ways of being a shark can fit into a tiny little dot in Latin America.