The Influence of Urbanization and Fire Disturbance on Plant-floral Visitor Mutualistic Networks

Abstract

The biodiversity loss resulting from rising levels of human impacts on ecosystems has been extensively discussed over the last years. The expansion of urban areas promotes drastic ecological changes, especially through fragmentation of natural areas. Natural grassland remnants surrounded by an urban matrix are more likely to undergo disturbance events. Since grassland ecosystems are closely related to disturbances such as fire and grazing, grassland plant communities, pollinators, and their interaction networks may be especially sensitive to urban expansion, because it promotes habitat fragmentation and modifies disturbance regimes. This work evaluated the effect of the level of urbanization and recent history of fire disturbance on grassland plants communities and plant-floral visitor mutualistic networks. We sampled plant communities and floral visitors in 12 grassland sites with different levels of urbanization and time since the last fire event. Sites with higher levels of urbanization showed higher values for plant species richness, floral visitor richness, and network asymmetry. All sampled networks were significantly nested (with one exception), asymmetric, and specialized. In addition, all networks presented more modules than expected by chance. The frequency of fire disturbance events increased with the level of urbanization. Since grassland ecosystems depend on disturbances to maintain their structure and diversity, we inferred that the history of fire disturbance was the mechanism behind the relationship between urbanization and our biological descriptors. Our findings highlight the importance of small and isolated grassland remnants as conservation assets within urban areas, and that the disturbance events that such sites are submitted to may in fact be what maintains their diversity on multiple levels.

Clearcutting and selective logging have inconsistent effects on liana diversity and abundance but not on liana–tree interaction networks

“…Based on previous studies which reported that disturbance reduces modularity in plant‐pollinator networks (Beal‐Neves et al., 2020; Pinho et al., 2017), we expected that modularity pattern would differ between the logged and old‐growth forests. On the contrary, there was no difference in modularity structure of liana–tree network between the logged and old‐growth forests.…”

Burning for grassland pollination: recently burned patches promote plant flowering and insect pollinators

“…Little is known about interactions of insect pollinators and plant communities in South Brazilian grasslands, but a few studies have indeed showed butterflies, bees, and beetles as abundant and frequent floral visitors in the study region (Pinheiro et al 2008;Oleques et al 2017;Beal-Neves et al 2020). Bee abundance and richness, and butterfly abundance were greatly amplified in freshly-burnt patches, largely attracted by floral resource improvement in these grasslands.…”

“…The Park rangers from PNMSH record an accurate burning history of each grassland site, and this was used as a basis to select burned patches used in this study. For the study region (including sites within the PNMSH), Beal-Neves et al, (2020) have shown a positive relationship between time-since-fire (as an indicative of fire frequency) and urbanization (proximity to urban areas), indicating that grassland patches closer to an urban matrix are more likely to burn. There are no historical records of wildfires, i.e., by natural causes, for the study region.…”

“…Nevertheless, the role of fire for conservation purposes in these ecosystems has been underestimated (Overbeck et al 2018). A few studies have shown positive patch burning effects on grassland arthropod faunas (Podgaiski et al 2013(Podgaiski et al , 2017Ferrando et al 2016) and, more recently, on mutualistic networks (da Silva et al 2020;Beal-Neves et al 2020). However, more investigations are necessary to better understand fire-induced changes though time in grassland habitat structure, flowering plants, and specifically on different insect pollinator groups.…”

Elucidating plant-pollinator interactions in South Brazilian grasslands: What do we know and where are we going?

“…Our search resulted in three plant community-level studies in the grasslands of the Pampa domain of Rio Grande do Sul (Pinheiro et al 2008;Oleques et al 2019;Beal-Neves et al 2020). In addition, were found another 23 case pollination studies from grasslands of both phytogeographical domains, including one unpublished manuscript (RS Avila Jr unpubl.…”