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Fire and grazing determined grasslands of central Madagascar represent ancient assemblages.

ABSTRACT: The ecology of Madagascar's grasslands is under-investigated and the dearth of ecological understanding of how disturbance by fire and grazing shapes these grasslands stems from a perception that disturbance shaped Malagasy grasslands only after human arrival. However, worldwide, fire and grazing shape tropical grasslands over ecological and evolutionary timescales, and it is curious Madagascar should be a global anomaly. We examined the functional and community ecology of Madagascar's grasslands across 71 communities in the Central Highlands. Combining multivariate abundance models of community composition and clustering of grass functional traits, we identified distinct grass assemblages each shaped by fire or grazing. The fire-maintained assemblage is primarily composed of tall caespitose species with narrow leaves and low bulk density. By contrast, the grazer-maintained assemblage is characterized by mat-forming, high bulk density grasses with wide leaves. Within each assemblage, levels of endemism, diversity and grass ages support these as ancient assemblages. Grazer-dependent grasses can only have co-evolved with a now-extinct megafauna. Ironically, the human introduction of cattle probably introduced a megafaunal substitute facilitating modern day persistence of a grazer-maintained grass assemblage in an otherwise defaunated landscape, where these landscapes now support the livelihoods of millions of people.

SUBMITTER: Solofondranohatra CL

PROVIDER: S-EPMC7287345 | biostudies-literature | 2020 May

REPOSITORIES: biostudies-literature

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Fire and grazing determined grasslands of central Madagascar represent ancient assemblages.

Solofondranohatra Cédrique L CL Vorontsova Maria S MS Hempson Gareth P GP Hackel Jan J Cable Stuart S Vololoniaina Jeannoda J Lehmann Caroline E R CER

Proceedings. Biological sciences 20200513 1927

The ecology of Madagascar's grasslands is under-investigated and the dearth of ecological understanding of how disturbance by fire and grazing shapes these grasslands stems from a perception that disturbance shaped Malagasy grasslands only after human arrival. However, worldwide, fire and grazing shape tropical grasslands over ecological and evolutionary timescales, and it is curious Madagascar should be a global anomaly. We examined the functional and community ecology of Madagascar's grassland ...[more]

PMID: 32396803

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Project description:Land-use and land-cover change associated with agriculture is one of the main drivers of biodiversity loss. In heavily modified agricultural landscapes, grazing lands may be the only areas that can provide essential resources for native grassland species. Management decisions, such as choice of livestock species, affect the extent to which grazing lands provide suitable habitat for native species such as pollinators.Our study compared how sheep versus cattle herbivory affected floral resources and butterfly abundance across low-diversity, former Conservation Reserve Program (CRP) pastures managed with patch-burn grazing.Across all years (2017-2019), flowering species richness and abundance were significantly higher in cattle pastures than sheep pastures. On average, we recorded 6.9 flowering species/transect in cattle pastures and 3.8 flowering species/transect in sheep pastures. The average floral abundance per transect was 1278 stems/transect in cattle pastures and 116 stems/transect in pastures grazed by sheep.Similarly, we observed higher butterfly species richness, diversity, and abundance in cattle than in sheep pastures. In cattle pastures, we observed an average of 75 butterflies and 6.75 species per transect, compared with an average of 52 butterflies and 3.37 species per transect in sheep pastures. However, the butterfly community composition did not significantly differ between grazing treatments likely because agricultural-tolerant, habitat generalists comprised the majority of the butterfly community. Five generalist butterflies comprised 92.3% of observations; Colias philodice was the most abundant (61% of observations). Speyeria idalia and Danaus plexippus, two butterflies of conservation concern, comprised less than 0.5% of butterfly observations.Our results, which are among the first attempt quantifying butterfly use of post-CRP fields grazed by livestock, show that increased precipitation and cattle grazing promoted higher forb abundance and richness. However, additional interventions may be needed to enhance floral resources to sustain and improve pollinator diversity in these landscapes.

Project description:Grazing exclusion may lead to biodiversity loss and homogenization of naturally heterogeneous and species-rich grassland ecosystems, and these effects may cascade to higher trophic levels and ecosystem properties. Although grazing exclusion has been studied elsewhere, the consequences of alleviating the disturbance regime in grassland ecosystems remain unclear. In this paper, we present results of the first five years of an experiment in native grasslands of southern Brazil. Using a randomized block experimental design, we examined the effects of three grazing treatments on plant and arthropod communities: (i) deferred grazing (i.e., intermittent grazing), (ii) grazing exclusion and (iii) a control under traditional continuous grazing, which were applied to 70 x 70 m experimental plots, in six regionally distributed blocks. We evaluated plant community responses regarding taxonomic and functional diversity (life-forms) in separate spatial components: alpha (1 x 1 m subplots), beta, and gamma (70 x 70 m plots), as well as the cascading effects on arthropod high-taxa. By estimating effect sizes (treatments vs. control) by bootstrap resampling, both deferred grazing and grazing exclusion mostly increased vegetation height, plant biomass and standing dead biomass. The effect of grazing exclusion on plant taxonomic diversity was negative. Conversely, deferred grazing increased plant taxonomic diversity, but both treatments reduced plant functional diversity. Reduced grazing pressure in both treatments promoted the break of dominance by prostrate species, followed by fast homogenization of vegetation structure towards dominance of ligneous and erect species. These changes in the plant community led to increases in high-taxa richness and abundance of vegetation-dwelling arthropod groups under both treatments, but had no detectable effects on epigeic arthropods. Our results indicate that decision-making regarding the conservation of southern Brazil grasslands should include both intensive and alleviated levels of grazing management, but not complete grazing exclusion, to maximize conservation results when considering plant and arthropod communities.

Dataset Information

Fire and grazing determined grasslands of central Madagascar represent ancient assemblages.

Publications

Fire and grazing determined grasslands of central Madagascar represent ancient assemblages.

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