Habitat loss and fragmentation disrupt community dynamics. Although we have evidence that habitat fragmentation decreases species biodiversity and also decreases dispersal, we know less about how fragmentation affects species interactions.
Interactions between species can be represented as a network that shows how species relate to each other in a community. In forested ecosystems, interactions between plants, aphids, and ants are a useful system for studying networks because these interactions can be both negative and positive. Aphids antagonistically feed on plant sap to the detriment of the plant, while ants mutualistically protect aphids from plant defenses in return for honeydew that aphids secrete.
Zhang, X., Dalsgaard, B., Staab, M., Chen, Z., Zhao, Y., Gonçalves, F., Ren, P., Cai, C., Qiao, G., Ding, P., and Si, X. 2023. Habitat fragmentation increases specialization of multi-trophic interactions by high species turnover. Proceedings of the Royal Society B 290: 20231372.
Recent research reveals how habitat loss and fragmentation change plant-aphid-ant networks in Thousand Island Lake in China, which is an artificial lake that contains over 1,000 islands varying in size and isolation from the mainland. On 18 of these islands, researchers surveyed woody plants to observe plant-aphid and aphid-ant interactions in 2020 and 2021, recording over 1,400 plant-aphid and 1,200 aphid-ant interactions.
They found that plant-aphid and aphid-ant networks were more specialized on smaller islands, meaning that species interacted with fewer partners. The number of species on these islands explain this trend – smaller islands supported fewer aphid and ant species, reducing the opportunity for a species to interact with many partners.
On more isolated islands, aphid-ant networks increased in specialization, but plant-aphid networks did not. Ants are more dispersal limited than aphids, so only specific ant species may be able to disperse to isolated islands, changing ant community composition. It’s possible that these long-dispersing ant species compete for the same aphid interactions, increasing network specialization on isolated islands.
Networks that are more specialized are often considered to be less stable because there is less redundancy in interactions. For example, if an aphid is dependent on one plant species, then a loss of that plant species would likely result in the local co-extinction of the aphid.
A key takeaway is that groups of interacting species are dependent on each other. Because plants, aphids, and ants constantly interact with each other, fragmentation effects on one group could have cascading effects on the others. In this case, the research found that species turnover in plant, aphid, and ant communities were linked, and this species turnover due to fragmentation affected interaction networks.
Species do not exist independently in an ecosystem – they are part of a complex web of interactions that keep ecosystems functioning. Understanding how species networks shift is important for the conservation of entire ecosystems, beyond just single species. With increasing habitat fragmentation, incorporating a multi-trophic perspective is important for predicting community dynamics in fragmented areas.
Related Posts
Policy choices shape landscape connectivity
A quantitative comparison of four possible policy paths in the mountains of China shows how different choices lead to dramatically different results for landscape connectivity.
Hybridization mitigates climate change risks for birds
Research on mountain birds shows that hybridization among species boosts their ability to adapt to rapid climate change, highlighting how natural corridors and gene flow can strengthen resilience in vulnerable high elevation ecosystems.
Forest edges and leaf functional traits impact decomposition
A study of over 7,000 shrub leaves shows that leaves on the edge of forests tend to be thicker and slower to break down when compared to leaves in the forest interior.
