An official website of the United States government
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
Loss of native herbivores triggers diversity decline of ephemeral plant communities
Abstract AimEvaluate the temporal changes in species diversity, composition, and structure of ephemeral plant communities and the seed bank in response to long‐term herbivore exclusion over 11 years in plots with and without herbivores. LocationNorth‐central Chile. MethodsWe obtained information on ephemeral vegetation cover in August and September using the intercept point method and recorded seed abundance in April. The Bosque Fray Jorge National Park Long‐Term Socio‐Ecological Research (LTSER) provided these records covering 11 years (2009–2019). From the original experiment of 20 plots, we used eight plots divided into two treatments: four plots allowed free access to all herbivores (with herbivores), while the other four plots excluded herbivores (without herbivores). ResultsWe found that Hill–Shannon diversity increased in plant communities with herbivores and a temporal increase in the cover of the dominant species,Plantago hispidula, under herbivore exclusion. In wet years, species richness and temporal turnover of plant communities increased independently of treatment. Although seed abundance differed among treatments and years, population structure remained constant over time and among treatments, suggesting that the seed bank acts as a buffer against shocks that modify plant community dynamics. Structural equation modeling revealed that precipitation, via its positive effects onPlantago hispidula, increases native plant richness to a greater extent than herbivores. However, in the absence of herbivores, precipitation directly affects native species richness. Moreover, we found that precipitation also influences the native species richness of the seed bank, both directly and indirectly, although its impacts exhibit a time lag. ConclusionsOur study demonstrates that the temporal dynamics of ephemeral plant communities and seed banks in semi‐arid ecosystems are strongly coupled to climate variability, highlighting the vulnerability of these communities to biodiversity loss and climate change.
more »
« less
- Award ID(s):
- 2025816
- PAR ID:
- 10518108
- Publisher / Repository:
- Journal of Vegetation Science
- Date Published:
- Journal Name:
- Journal of Vegetation Science
- Edition / Version:
- 1
- Volume:
- 34
- Issue:
- 5
- ISSN:
- 1100-9233
- Subject(s) / Keyword(s):
- dominance, herbivores, long-term experiments, plant diversity, Plantago hispidula, seed bank, small mammals, temporal turnover
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Whether wild herbivores confer biotic resistance to invasion by exotic plants remains a key question in ecology. There is evidence that wild herbivores can impede invasion by exotic plants, but it is unclear whether and how this generalises across ecosystems with varying wild herbivore diversity and functional groups of plants, particularly over long‐term (decadal) time frames.Using data from three long‐term (13‐ to 26‐year) exclosure experiments in central Kenya, we tested the effects of wild herbivores on the density of exotic invasive cacti,Opuntia strictaandO. ficus‐indica(collectively,Opuntia), which are among the worst invasive species globally. We also examined relationships between wild herbivore richness and elephant occurrence probability with the probability ofO. strictapresence at the landscape level (6150 km2).Opuntiadensities were 74% to 99% lower in almost all plots accessible to wild herbivores compared to exclosure plots.Opuntiadensities also increased more rapidly across time in plots excluding wild herbivores. These effects were largely driven by megaherbivores (≥1000 kg), particularly elephants.At the landscape level, modelledOpuntia strictaoccurrence probability was negatively correlated with estimated species richness of wild herbivores and elephant occurrence probability. On average,O. strictaoccurrence probability fell from ~0.56 to ~0.45 as wild herbivore richness increased from 6 to 10 species and fell from ~0.57 to ~0.40 as elephant occurrence probability increased from ~0.41 to ~0.84. These multi‐scale results suggest that any facilitative effects ofOpuntiaby wild herbivores (e.g. seed/vegetative dispersal) are overridden by suppression (e.g. consumption, uprooting, trampling).Synthesis. Our experimental and observational findings that wild herbivores confer resistance to invasion by exotic cacti add to evidence that conserving and restoring native herbivore assemblages (particularly megaherbivores) can increase community resistance to plant invasions.more » « less
-
Abstract Anthropogenic nutrient enrichment and shifts in herbivory can lead to dramatic changes in the composition and diversity of aboveground plant communities. In turn, this can alter seed banks in the soil, which are cryptic reservoirs of plant diversity. Here, we use data from seven Nutrient Network grassland sites on four continents, encompassing a range of climatic and environmental conditions, to test the joint effects of fertilization and aboveground mammalian herbivory on seed banks and on the similarity between aboveground plant communities and seed banks. We find that fertilization decreases plant species richness and diversity in seed banks, and homogenizes composition between aboveground and seed bank communities. Fertilization increases seed bank abundance especially in the presence of herbivores, while this effect is smaller in the absence of herbivores. Our findings highlight that nutrient enrichment can weaken a diversity maintaining mechanism in grasslands, and that herbivory needs to be considered when assessing nutrient enrichment effects on seed bank abundance.more » « less
-
{"Abstract":["This study investigated the question, "Does climate change\n affect vegetation and seed bank composition in desert\n grasslands?" The work was done in the Sevilleta National\n Wildlife Refuge, New Mexico, USA, in in the Extreme Drought in\n Grassland Experiment (EDGE). Vegetation and seed bank species\n composition were recorded in black grama (Bouteloua eriopoda) and\n blue grama (B. gracilis) grasslands at Sevilleta. At each site, two\n rainfall manipulations and ambient controls were established in 2013\n (n=10). Treatments included extreme drought (-66% rainfall\n reduction) and delayed monsoon (precipitation captured during\n July-August and reapplied during September-October). Aboveground\n species composition was assessed and composite soil samples were\n collected in 2017, five years after the experiment started. Seed\n bank composition was evaluated using the seedling emergence method.\n Rainfall treatments increased aboveground species richness at both\n sites, and seed bank richness only in the blue grama community.\n Vegetation cover was reduced by both rainfall manipulations, but\n seed bank density increased or remained the same compared with\n controls. In aboveground vegetation, cover of annual and perennial\n forbs increased, and dominant perennial grasses decreased. In the\n soil seed bank, species composition was similar among all treatments\n and was dominated by annual and perennial forbs. The seed bank was\n more resistant to drought than aboveground vegetation. Because seed\n banks enhance long-term community stability, their drought\n resistance plays an important role in maintaining ecosystem\n processes during and following drought in these grassland\n communities."]}more » « less
-
The harsh geophysical template characterized by the urban environment combined with people’s choices has led ecologists to invoke environmental filtering as the main ecological phenomena explaining urban biodiversity patterns. Yet, dispersal is often overlooked as a driving factor, especially on expanding vacant land. Does overcoming dispersal limitation by seeding native species in urban environments and increasing the functional or phylogenetic diversity of the seeding pool increase native plant species diversity and abundance in urban vacant land? We took an experimental approach to learn how different dimensions of plant biodiversity within an augmented regional species pool, via seed additions, can explain variation in community structure over a 3-year period. Vacant lots were cleared and manipulated with seeding treatments of high or low phylogenetic and functional diversities from a pool of 28 native species. Establishment success, total native cover and native species richness were followed and compared to cleared, unseeded control lots as well as un-manipulated lots. Seeding increased native plant abundance and richness over uncleared plots, as well as cleared and unseeded control plots. Phylogenetically diverse seed mixtures had greater establishment success than mixtures composed of closely related species. Diversifying seed mixtures increased the likelihood of including species that are better able to establish on vacant land. However, there were no differences in varying levels of either functional or phylogenetic diversity. Augmenting the regional species pool via diverse seed mixtures can enhance native plant cover and richness under the harsh environmental conditions conferred by land abandonment.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1111/jvs.13210
