Beyond network-based approaches: uncovering the true cost of connectivity

Context Fragmented landscapes challenge biodiversity conservation. While connectivity elements are promoted to mitigate the effects of fragmentation, their effectiveness remains debated. Objectives This study evaluates the effectiveness of corridors and stepping stones in enhancing dispersal success and population dynamics in a high-resistance matrix. We compare two experimental approaches: a landscape-based design that explicitly accounts for matrix resistance, and a traditional network-based design in which habitat patches are connected by tubes. Methods We conducted a laboratory experiment using the microarthropod model Folsomia candida , manipulating fragmentation by varying the distance between four habitat patches embedded in a high-resistance matrix. Connectivity elements (corridors and stepping stones) were tested and compared with unconnected landscapes (control) and network-based designs. Over 12 weeks, we monitored colonization success, population size, reproduction rate, and adult survival using AI-based image analysis. Results The presence of corridors as a connectivity element enhanced the colonization of initially empty patches, but their effectiveness was distance-dependent. Stepping stones did not differ from the non-connected control landscapes. Interestingly, the largest total populations were found in the non-connected control landscapes, where restricted dispersal resulted in higher reproduction, indicating a trade-off between movement and reproduction. The highest mortality of released adults was observed in landscapes with corridors, whereas higher recruitment was observed in stepping stones landscapes. Network-based designs yielded a higher population size in initially empty patches compared to landscape-scale designs. However, as they bypassed matrix-related dispersal costs, they led to a miss-estimation of the movement, reproduction, survival and recruitment processes. Conclusions Connectivity elements can support dispersal and reproduction, but may also increase mortality in resistant matrices. Conservation strategies should incorporate matrix resistance and landscape-scale context to better promote population dynamics in fragmented landscapes.