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Contributed Poster

Poster Type: Contributed Poster

Poster Session:: Communities: Spatial Patterns And Environmental Gradients

PS 13-132 - Competition and aspect contribute to saxicolous lichen species distribution on serpentine outcroppings

Monday, August 15, 2022

5:00 PM – 6:30 PM EDT

Located in: ESA Exhibit Hall

Coauthor(s)

Ts

Tim sisneros

University of California Los Angeles, United States
AC

Avalon Conklin

University of California Santa Cruz, United States
CH

Charles Hu

University of California Merced, United States

Presenting Author(s)

KG

Kathryn Gerhardt

University of California Santa Cruz, United States

Background/Question/Methods

This study was conducted on serpentine outcrops in Sedgwick Reserve, California where we observed numerous different species of lichen growing on the same rocks. There exist mechanisms that allow for many species to coexist on the same limited resources including, niche partitioning, and the theory of intransitivity (an ecological game of “rock-paper scissors”). Our study investigated the distribution of lichen communities on serpentine outcroppings to evaluate if the coexistence mechanisms of niche partitioning and/or intransitivity could be maintaining the diversity of species that we observed. We identified five different common species of crustose lichens to focus on. To test for niche partitioning, we sampled random rocks on the outcrops and took photos of a flexible quadrat placed on the north, east, south, west, and top faces of the rocks. We analyzed the percent cover of our lichen species using imageJ software to see if the species were distributing by rock face. To observe competitive interactions, we deliberately found rocks where two of our lichen species were growing next to each other to observe. We counted a win as one species growing on top of the other and quantified the proportion of wins to losses in each pairwise interaction.

Results/Conclusions

We observed a clear hierarchical competitive system with no evidence of intransitive interactions. We found that different lichen species distribute themselves differently according to the aspect of the rock on which they grew (n =175, p = < 0.0001) providing evidence for niche partitioning. The aspect of the rock was also found to support the variance in the distribution of the lichen species (n = 175, p = < 0.0001). In competitive interactions, the most common lichen observed was the second strongest competitor. The strongest competitive species however covered the least area on any rock face. This may indicate that lichens are most successful when adopting strategies that included both fast growth and some level of competitive overtopping ability. Competition via overlapping may be too energy-intensive in harsh environments. Although a thick growth form might be better at directly overtaking other lichens, the area that the lichen can overtake per unit time may be severely reduced with this strategy, especially on an easily erodible rock surface such as serpentinite. These findings have implications for not only the energetic trade-offs that may accompany competitive strategies but for the ability of species to coexist via spatial resource partitioning.