An official website of the United States government
This study examines how global changes in large herbivore populations (declining wild herbivores and increasing domestic herbivores) interacts with climate to influence plant communities by utilizing a large herbivore exclosure experiment in an oak savanna ecosystem in California with three herbivore assemblages (all herbivores, cattle-only excluded, all large herbivores excluded) across a topo-climatic gradient. Samples of plants were collected and processed to measure specific leaf area (SLA), leaf area (LA), and leaf dry matter content (LDMC). Additional traits (leaf nitrogen content and seed mass) were determined via web database searches. The finding of this study highlight complex interactions between herbivore assemblages and climate.
more »
« less
Interactive Effects of Climate and Large Herbivore Assemblage Drive Plant Functional Traits and Diversity
Large herbivore communities are changing globally, with populations of wild herbivores generally declining while domestic herbivore populations are increasing, influencing ecosystem function along with the impacts of climate change. Manipulative experiments have rarely captured the interaction between patterns of large herbivore assemblage change and climatic conditions. This interaction may affect the functional traits and functional diversity of herbaceous communities; this requires investigation, as these metrics have been useful proxies for ecosystem function. We used a large herbivore exclosure experiment replicated along a topo-climatic gradient to explore the interaction between climate and herbivore assemblage on community-level functional traits and the functional diversity of herbaceous plant understories. Our findings demonstrate interacting effects between large herbivore assemblages and climate. We found a shift from drought-tolerant traits to drought-avoidant traits with increasing aridity, specifically with regard to plant leaf area and specific leaf area. We also determined that plant community responses to grazing changed from an herbivore avoidance strategy at drier sites to a more herbivore-tolerant strategy at wetter sites. We observed that the effects of herbivores on community-level traits can sometimes counteract those of climate. Finally, we found that cattle and large wild herbivores can differ in the magnitude and direction of effects on functional traits and diversity.
more »
« less
- Award ID(s):
- 1900502
- PAR ID:
- 10673289
- Publisher / Repository:
- Plants
- Date Published:
- Journal Name:
- Plants
- Volume:
- 14
- Issue:
- 8
- ISSN:
- 2223-7747
- Page Range / eLocation ID:
- 1249
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Large mammalian herbivores exert strong top‐down control on plants, which in turn influence most ecological processes. Accordingly, the decline, displacement, or extinction of wild large herbivores in African savannas is expected to alter the physical structure of vegetation, the diversity of plant communities, and downstream ecosystem functions. However, herbivore impacts on vegetation comprise both direct and indirect effects and often depend on herbivore body size and plant type. Understanding how herbivores affect savanna vegetation requires disaggregating the effects of different herbivores and the responses of different plants, as well as accounting for both the structural complexity and composition of plant assemblages. We combined high‐resolution Light Detection and Ranging (LiDAR) with field measurements from size‐selective herbivore exclosures in Kenya to determine how herbivores affect the diversity and physical structure of vegetation, how these impacts vary with body size and plant type, and whether there are predictable associations between plant diversity and structural complexity. Herbivores generally reduced the diversity and abundance of both overstory and understory plants, though the magnitude of these impacts varied substantially as a function of body size and plant type: only megaherbivores (elephants and giraffes) affected tree cover, whereas medium‐ and small‐bodied herbivores had stronger effects on herbaceous diversity and abundance. We also found evidence that herbivores altered the strength and direction of interactions between trees and herbaceous plants, with signatures of facilitation in the presence of herbivores and of competition in their absence. While megaherbivores uniquely affected tree structure, medium‐ and small‐bodied species had stronger (and complementary) effects on metrics of herbaceous vegetation structure. Plant structural responses to herbivore exclusion were species‐specific: of five dominant tree species, just three exhibited significant individual morphological variation across exclosure treatments, and the size class of herbivores responsible for these effects varied across species. Irrespective of exclosure treatment, more species‐rich plant communities were more structurally complex. We conclude that the diversity and architecture of savanna vegetation depend on consumptive and nonconsumptive plant–herbivore interactions; the roles of herbivore diversity, body size, and plant traits in mediating those interactions; and a positive feedback between plant diversity and structural complexity.more » « less
-
Abstract The replacement of grasses by shrubs or bare ground (xerification) is a primary form of landscape change in drylands globally with consequences for ecosystem services. The potential for wild herbivores to trigger or reinforce shrubland states may be underappreciated, however, and comparative analyses across herbivore taxa are sparse. We sought to clarify the relative effects of domestic cattle, native rodents, native lagomorphs, and exotic African oryx (Oryx gazella) on a Chihuahuan Desert grassland undergoing shrub encroachment. We then asked whether drought periods, wet season precipitation, or interspecific grass–shrub competition modified herbivore effects to alter plant cover, species diversity, or community composition. We established a long‐term experiment with hierarchical herbivore exclosure treatments and surveyed plant foliar cover over 25 years. Cover of honey mesquite (Prosopis glandulosa) proliferated, responding primarily to climate, and was unaffected by herbivore treatments. Surprisingly, cattle and African oryx exclusion had only marginal effects on perennial grass cover at their current densities. Native lagomorphs interacted with climate to limit perennial grass cover during wet periods. Native rodents strongly decreased plant diversity, decreased evenness, and altered community composition. Overall, we found no evidence of mammalian herbivores facilitating or inhibiting shrub encroachment, but native small mammals interacting with climate drove dynamics of herbaceous plant communities. Ongoing monitoring will determine whether increased perennial grass cover from exclusion of native lagomorphs and rodents slows the transition to a dense shrubland.more » « less
-
Abstract Plant traits can be helpful for understanding grassland ecosystem responses to climate extremes, such as severe drought. However, intercontinental comparisons of how drought affects plant functional traits and ecosystem functioning are rare. The Extreme Drought in Grasslands experiment (EDGE) was established across the major grassland types in East Asia and North America (six sites on each continent) to measure variability in grassland ecosystem sensitivity to extreme, prolonged drought. At all sites, we quantified community‐weighted mean functional composition and functional diversity of two leaf economic traits, specific leaf area and leaf nitrogen content, in response to drought. We found that experimental drought significantly increased community‐weighted means of specific leaf area and leaf nitrogen content at all North American sites and at the wetter East Asian sites, but drought decreased community‐weighted means of these traits at moderate to dry East Asian sites. Drought significantly decreased functional richness but increased functional evenness and dispersion at most East Asian and North American sites. Ecosystem drought sensitivity (percentage reduction in aboveground net primary productivity) positively correlated with community‐weighted means of specific leaf area and leaf nitrogen content and negatively correlated with functional diversity (i.e., richness) on an intercontinental scale, but results differed within regions. These findings highlight both broad generalities but also unique responses to drought of community‐weighted trait means as well as their functional diversity across grassland ecosystems.more » « less
-
The U.S. Pacific Northwest (PNW) hosts an extensive suite of Miocene-aged fossil plants sites, with the potential to document changes in plant community ecology in response to regional climatic change during the Miocene Climatic Optimum (MCO; 17-14 Ma) and the ensuing Middle Miocene Climatic Transition (MMCT; ~14 Ma). The MCO was the most recent period of sustained global warming and thus provides some analogy to anthropogenic climate change. An important component of characterizing plant community ecology is the diversity and prevalence of ecological strategies present within a community. Many previous paleoecology studies rely on a nearest living relative approach to infer components of ecological strategy (e.g., plant functional types) from fossil plant assemblages. In contrast, much work in neo-ecology stresses the importance of functional traits in elucidating prevalent ecological strategies and functional diversity within plant communities. Here we take advantage of exquisitely preserved leaf compression fossils from Clarkia, northern Idaho (~16.9 Ma), representing the height of the MCO, to measure leaf functional traits and elucidate ecological strategies of dominant species in this ancient temperate mixed conifer-deciduous-evergreen forest. We focus on 13 species, representing the most abundant angiosperm taxa in the assemblage, including Betula, Castanea, and Quercus. We reconstruct assimilation rates using gas exchange modeling, address leaf hydraulic efficiency by measuring leaf vein density, and reconstruct water use efficiency by accounting for the ratio of carbon assimilation to transpirational water loss. As these species are prevalent in many other Miocene floras of the PNW, this study provides a benchmark by which to interpret changes in the dominance or presence of these species through time and, by inference, how Miocene climatic changes impact the functional composition and diversity of this forest type. We are also providing an example of how present-day mixed deciduous forests may respond to current anthropogenic changes in CO 2.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.3390/plants14081249
