Abstract Detail


Peyton, Michael [1], Hotchkiss, Sara [2].

An investigating into the role of functional traits and spatial scale in Hawaiian understory responses to pig disturbance.

While the effects of species introductions on biotic interactions receive much attention1–3, non-native species can also profoundly affect abiotic conditions and disturbance regimes4–6. Disturbance facilitated by non-native pig activity has radically altered vegetation communities worldwide5,7–9. Hawai‘i, with no history of native ungulates but with substantial invasion by plant species adapted for ungulate disturbance6,10,11, provides an ideal test case to investigate the mechanisms driving differential species responses to ungulate activity. These effects likely vary by spatial scale12 since plant establishment and growth are influenced by the extent of disturbance within a habitat patch as well as within the surrounding habitat mosaic13. Species traits, particularly those involved in regulating carbon capture and dispersal, should influence responses14,15. Here we use the framework of resource “acquisitive” vs “conservative” leaf traits as described by the leaf economic spectrum16–18. Frequent disturbance typically favors species with fast growth rates and high dispersal ability to colonize recently cleared patches and persist as metapopulations on disturbed sites19. Thus, we hypothesize that species possessing resource acquisitive leaf traits and smaller propagules will be favored in the presence of pig activity.
We delineated four 1-km2 sites ranging from pig absence to high pig density on Kohala Mountain using monitoring data from Hawai‘i’s Natural Areas Reserve System and population density estimates from a 2018 camera trap survey. We conducted hierarchically structured understory vegetation surveys at two scales: small habitat patches in quadrats nested within local community assemblages along transects. We used linear mixed-effects models to test the effects of pig activity on native and non-native plant species richness. We used principal components analysis on key functional traits associated with growth and reproduction to understand trait differences among native and non-native species. We then investigated the role of plant function on the impact of soil disturbance using phylogenetically constrained multi-level models (MLM).
Disturbance at both spatial scales increased non-native plant richness while decreasing native richness. However, the effect of disturbance within individual habitat patches was mediated by the extent of disturbance in the surrounding community for non-native species. Species varied primarily in traits influencing leaf investment and carbon capture (PC1, 46.3% variance explained)16,18, and secondarily in traits influencing dispersal and stress tolerance (PC2, 24.7% variance explained)20,21. Non-native species more often exhibited acquisitive traits than did native species. The MLM confirmed that resource acquisitive species are favored in the presence of pig disturbance, likely due to the ability to establish and grow rapidly in cleared patches19,22 and the reduced investment cost of high-N leaves from increased nutrient availability in disturbed sites23. Species possessing acquisitive traits demonstrated divergent responses at patch and local scales to the interaction of light availability and disturbance, highlighting the influence of spatial scale on response mechanisms. Model results indicated dispersal and stress tolerance were not important drivers of species responses to disturbance, likely due to a lack of dispersal limitation. Thus, leaf construction and associated carbon capture rates are likely the primary factors driving turnover in response to pig activity.

1 - University Of Wisconsin Madison, Botany, 430 Lincoln Dr, Madison, WI, 53706, United States
2 - University Of Wisconsin-Madison, Botany, 430 Lincoln Drive, Madison, WI, 53706, United States

functional traits
community assembly

Presentation Type: Oral Paper
Number: EC09002
Abstract ID:694
Candidate for Awards:Ecological Section Best Graduate Student Paper

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