Multi-habitat landscapes are more diverse and stable with improved function

Conservation efforts are increasingly shifting towards landscape-scale approaches, yet a mechanistic understanding of how habitat number influences community structure and function remains limited. This is particularly crucial for ecosystem services reliant on species interactions, such as pollination and pest control. While ecological networks offer a pathway to understanding functional responses to biodiversity changes, datasets encompassing multiple guilds and habitats are scarce. Existing studies have linked networks across habitats or interaction types, but often lack independent functional measures, hindering a complete understanding. The research question is whether landscape-level properties emerge from multiple habitats that are not simply the sum of their parts, affecting community structure, stability, and function. The study's importance lies in providing a mechanistic understanding of how habitat diversity contributes to landscape-scale ecosystem services and resilience to biodiversity loss. This knowledge is crucial for informing effective landscape management and conservation strategies.

Previous research has established the positive effects of habitat heterogeneity and number on species richness and ecosystem function, particularly in agricultural landscapes. However, a mechanistic understanding of how habitat number contributes to community structure and function has been lacking. Studies have begun linking networks across habitats or interaction types, but often lack independent measures of function, preventing mechanistic links between network changes and functional outcomes. The influence of organism dispersal between habitats on local community structure and function has been investigated, exploring concepts like redundancy and complementarity. However, the question of whether landscapes are merely the sum of their habitat parts or if emergent properties exist remained unanswered. This study aims to address this gap by examining multiple interaction types across replicate landscapes with varying habitat numbers.

The study used 30 independent 9-ha field sites in southwest UK, categorized into monads (one habitat), dyads (two habitats), and triads (three habitats). Six habitat types were included: grassland, heathland, woodland, salt marsh, sand dune, and scrub. Data on 11,482 interactions among 154 plant species and 954 insect species were collected across multiple guilds (plant-pollinator, three types of plant-herbivore-parasitoid). Community diversity and structure were assessed through metrics like species richness, abundance, and evenness. Community robustness to species loss was calculated by simulating plant species removal (from least to most abundant), accounting for rewiring and shared species between interaction types. A manipulative field experiment using potted *Fragaria vesca* (strawberry) plants examined the effect of habitat number on pollination function (fruit weight and quality). Finally, a null model approach compared interaction evenness and complementarity in empirical triads with null triads constructed from component habitat data to identify emergent properties.

Multi-habitat landscapes (dyads and triads) showed significantly higher insect species richness, abundance, evenness, and interaction evenness compared to single-habitat landscapes (monads). While plant species richness showed a non-significant increase from monads to triads, interaction evenness increased significantly. There was no significant difference in mean community robustness across habitat numbers, but robustness variability decreased significantly as habitat number increased. The field experiment demonstrated that although strawberry fruit weight did not differ, triads yielded a significantly higher proportion of high-quality (Class I) fruits, indicating more effective pollination. This was attributed to higher interaction complementarity among pollinator species in triads, not increased pollinator abundance or richness. The null model analysis revealed that interaction evenness was higher and complementarity lower in empirical triads than in null triads, suggesting emergent properties beyond simple additive effects of individual habitats. Plant phylogenetic diversity correlated positively with interaction complementarity and negatively with interaction evenness, potentially contributing to observed patterns.

The findings strongly support the hypothesis that multi-habitat landscapes exhibit emergent properties leading to improved community structure, stability, and function. The increased species and interaction evenness contribute to higher functional diversity and resilience to species loss. The enhanced pollination success in triads highlights the importance of interaction complementarity driven by habitat diversity. The null model results confirm that the observed patterns are not simply additive effects of individual habitats but reflect emergent properties of multi-habitat configurations. The relationship between landscape heterogeneity, interaction evenness, and plant phylogenetic diversity provides a mechanistic explanation for the improved community stability and function. These findings have significant implications for conservation and land management strategies, emphasizing the importance of maintaining diverse and connected natural habitats for bolstering ecosystem services and resilience to environmental change.

This study demonstrates that multi-habitat landscapes support more diverse, stable, and functionally effective plant-insect communities than single-habitat landscapes. The improved pollination efficiency and increased robustness to species loss highlight the importance of habitat diversity in maintaining ecosystem services. Future research should investigate the long-term effects of habitat configuration on community dynamics, exploring the interplay of different interaction types and the influence of environmental stressors. Further research using path analysis and additional replication could refine our understanding of how landscape heterogeneity influences community stability through different mechanisms.

The study focused on spatial variability across a landscape and did not consider temporal dynamics. While the null model analysis provided evidence for emergent properties, it was based on plant-pollinator networks and might not fully generalize to all interaction types. The sampling design, while balanced, may not capture the full range of possible habitat combinations and their impacts. Additionally, the study's findings are specific to the geographical region and habitats investigated.