The timeless adage “sticks and stones may break your bones” takes on a fascinating twist when we shift our focus from playground banter to the intricate ecosystems inhabited by coastal giant salamanders. Beyond mere linguistic constructs, in the cool shadows of forests, sticks and stones emerge as geological and ecological forces shaping the destiny of these remarkable amphibians.
In the intricate tapestry of nature, coastal giant salamanders emerge as protagonists in a story woven by the elements of their habitat. The unseen threads of habitat conditions weave a narrative that stretches from the vastness of large creeks to the smaller silt-laden pools, where salamander larvae navigate a world influenced by water and earth.
The researchers of this study (henceforth referred to as the Orchestrators) embarked on this scientific odyssey into the Angelo Coast Range Reserve. The landscape and vegetation of this natural reserve in Northern California provided an opportunity to study the intersections of habitat and salamander diversity. By virtue of its protection, this area is a relatively undisturbed section of nature conducive to studying natural interactions. The quest of the Orchestrators was to uncover the nuanced ecological influences of creek beds and submerged rocks that govern Dicamptodon tenebrosus, or coastal giant salamander populations. These geological entities, often overlooked in the broader canvas of ecosystems, manifested as key questions of the complex ecological composition, potentially impacting salamander larvae population density and size. Forming oases of habitat for these majestic beasts, these regions are areas of high interest for conservation and biodiversity. Learning their essence and rhythms is an avenue for replicating more of these islands of song and sound, and the beginning of a safer future for the salamanders.
The symphony of nature played out in these waters, as larger creeks boasted a crescendo of cover rocks – a haven for macroinvertebrates. Changes in population of top predators can cascade to lower trophic levels, where consumers control the behavior and density of species lower in the web. For example whitetail dragonfly, where increased diversity of size classes led to cannibalism of smaller individuals through top-down trophic control. In coastal giant salamander, Dicamptodon tenebrosus, the abiotic factors that affect population density had been studied well before, but little was known about the effect of abiotic factors on larval body size. The criteria of the study conducted by the Orchestrators took into consideration creek size, density of cover rocks, silt levels, larval population density, and larval size. The Orchestrators hypothesized that larval population density would increase proportionally with higher density of cover rocks, lower percentage of silt, and larger salamander larvae. Larger islands would shape the growth trajectories of coastal giant salamander larvae, resulting in larger sizes. Conversely, the gentle murmurs of fine sediment in smaller creeks would compose a softer, yet more impactful undertone.
Venturing into this realm where scientific inquiry met the artistry of nature, the Orchestrators unraveled a tale where geological forces became the protagonists in a drama that transcended the boundaries between scientific exploration and the creative tapestry of the natural world. The South Fork Eel River, once inhabited by the Cahto people, bursts into song, but not all at once. The South Fork Eel River is the largest tributary of the Eel River, once inhabited by the Pomo people, a Native American people of California that relied on the salmon and steelhead. In little pools of twinkling notes, mystical waves wash over every nook and crevice. One of the pools was Fox Creek, with its medium flow rates, abundance of gravel, and high silt, with a drainage area (DA) of 2.8 km2. The second was McKinley Creek, with slower flow rates but higher silt, and a DA of 0.58 km2. The third was Elder Creek with fast flow rate and similar gravel and silt to McKinley Creek, with a DA of 13.5 km2. The Orchestrators crouched on the banks of each creek and observed the sounds that passed.
In gentle but firm movements, they dipped their hands into cool and clear water to select the individuals of study. In each stagnant, rocky pool were larvae that hid under rocks where they could find their delicious diet of mayflies, stoneflies, and damselflies provided by the sheltering rocks. The Orchestrators surveyed twenty pools per creek, measuring the duration and size of each section, limiting their studies to pools of 2 meters in length and width and 35 centimeters deep. To fully grasp the artistry of this performance, they counted all unembedded rocks over 7.5 centimeters to measure rock cover density, and calculated rock density by dividing the number of rocks by the pool’s area.
The salamanders in their creeks were measured by their snout-to-vent length (SVL), a metric akin to measuring human height, where the snouts of the larvae represent the front and vents the rear end. SVL is a common metric used in herpetology, the branch of zoology concerned with studying amphibians and reptiles. Relationships between rock and larval population density were analyzed using a statistical model to estimate linear relationships known as linear regression. Amidst the ebb and flow of this ecosystem, the conductor waved away.
In the aquatic symphony of coastal giant salamanders, rock abundance orchestrated a mesmerizing surge in Dicamptodon tenebrosus numbers, where the p-value, or probability due to chance, was less than 0.0001. Surprisingly, the percentage of silt cover remained a silent spectator in this watery performance, showing no significant effect on larval population density (p>0.88). Across diverse creek landscapes, the large creek flaunted rock-laden allure, with directly proportional rock coverage (p = 0.08), while small creeks unveiled a silt-rich spectacle (p<0.0001). Yet, amidst these ecological theatrics in the three creeks, larval density remained a harmonious constant, with no significant difference in their numbers (p = 0.93). In smaller creeks, the larval size also shrank, being significantly smaller than their medium and large creek neighbors (0.0002). To capture the essence of peer pressure, the presence of large D. tenebrosus had a marginally positive effect on the mean SVL of the remaining individuals in the same pool (p = 0.055). Nature’s captivating choreography unfolded beneath the surface, where rocks, silt, and salamanders composed an enchanting symphony of life.
Journeying through this theatrical performance brought the Orchestrators to the crossroads of salamander body size, their larval density, rock density of creek, flow speed, and silt levels. Data supported the Orchestrator’s hypotheses that the average larvae are sized smaller in a smaller creek than in medium and large sized ones. However, data less affirmed the claim that medium and large creeks would affect the larval body size.
In the staff of this ensemble, a higher density of rocks was hypothesized to be more homely for larvae due to the shelter provided for them. The larvae had options this way – more places to hide and nurture themselves. Incoming traffic from the flow of water brought more bugs and critters for larvae to feed on, increasing their chances of survival and their body sizes. Larger salamander larvae had greeted competitive and cannibalistic advantages as they could easily consume smaller larvae and shift trophic dynamics. Overall changes in adult salamander population impacted the larvae feeding behavior, and cascaded down to the ecosystem into the pool that is a trophic relationship. Abiotic factors at this intersectional crossroads affected the function of the top predator in the ecosystem, and could be an integral component of conservation efforts.
The elements in this universe compose a harmonious symphony, forming a complex interplay between individuals and ecosystems. The symphony in this world may be conducted by one master of the elements of nature, but not one masterpiece would emanate from an orchestra with one player.