Small habitats, big consequences: Connectivity loss in pond networks threatens microbial biodiversity

In the midst of the ongoing global biodiversity crisis, even the smallest habitats like ponds demand our attention. Fragmentation of these habitats—driven by human activities like urbanization, agriculture, and land-use changes—poses a significant threat to biodiversity. Often overlooked in conservation efforts, ponds serve as vital ecological hotspots, supporting diverse species and sustaining essential ecosystem processes. These waterbodies are home to various microbial communities that, despite their tiny size play an indispensable role in ecosystem functioning, acting as primary producers, decomposers, and links in food webs. While the impacts of habitat fragmentation on large organisms like mammals and birds are well-documented, the effects on microscopic organisms, including bacteria, algae, and other unicellular eukaryotes remain poorly understood.

A recent study carried out by researchers from HUN-REN Centre for Ecological Research in Hungary explored the effects of connectivity loss within pond networks. Using an outdoor experimental setup of artificial ponds (mesocosms), the researchers simulated fragmentation by terminating the movement of water and organisms between habitats in half of the pond networks while maintaining dispersal in the other half. By controlling for factors like habitat size and environmental conditions, and focusing solely on connectivity loss, the study provided an insight into the direct impacts of fragmentation on biodiversity.

“Our findings were particularly striking for unicellular microeukaryotes. Connectivity loss led to significant declines in their diversity at both local and regional levels, highlighting that fragmentation can directly drive biodiversity loss, even under controlled circumstances. Both rare and abundant species were impacted, suggesting that fragmentation represents a widespread and severe threat to microbial biodiversity. In contrast, prokaryotes appeared more resilient, though we observed signs of a potential “extinction debt,” where biodiversity loss may emerge over longer timescales.” – explains Dr. Beáta Szabó, the first author of the study.

Beyond biodiversity, the study also highlighted how connectivity loss disrupts trophic interactions. Zooplankton grazers, which interact closely with microbial communities, experienced reduced biomass in fragmented habitats, further exacerbating the decline in diversity and community evenness of microeukaryotes. These findings highlight the interdependence of organism groups within ecosystems and the cascading impacts that habitat fragmentation can have on biodiversity and ecosystem functioning.

“Our study clearly demonstrates that habitat fragmentation—specifically the loss of connectivity—can have serious and far-reaching consequences for biodiversity. Even when habitat size or environmental conditions remain constant, simply disrupting the dispersal of individuals between habitats can trigger significant declines in microbial diversity. Conservation efforts must not only focus on preventing habitat destruction, particularly in vulnerable ecosystems like pond networks, but also prioritize maintaining and restoring connectivity between habitats to protect the ecosystems and species that rely on them. This is especially crucial for microbes, which, despite their small size, have enormous ecological significance." – summarizes Dr Zsófia Horváth, the senior author of the study and head of the Biodiversity and Metacommunity Ecology Research Group at Institute of Aquatic Ecology, HUN-REN Centre for Ecological Research.

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