Abstract
The dynamics of ecological communities depend partly on species interactions within and among trophic levels. Experimental work has demonstrated the impact of species interactions on the species involved, but it remains unclear whether these effects can also be detected in long‐term time series across heterogeneous landscapes. We analyzed a 19‐yr time series of patch occupancy by the Glanville fritillary butterfly Melitaea cinxia, its specialist parasitoid wasp Cotesia melitaearum, and the specialist fungal pathogen Podosphaera plantaginis infecting Plantago lanceolata, a host plant of the Glanville fritillary. These species share a network of more than 4,000 habitat patches in the Åland islands, providing a metacommunity data set of unique spatial and temporal resolution. To assess the influence of interactions among the butterfly, parasitoid, and mildew on metacommunity dynamics, we modeled local colonization and extinction rates of each species while including or excluding the presence of potentially interacting species in the previous year as predictors. The metapopulation dynamics of all focal species varied both along a gradient in host plant abundance, and spatially as indicated by strong effects of local connectivity. Colonization and to a lesser extent extinction rates depended also on the presence of interacting species within patches. However, the directions of most effects differed from expectations based on previous experimental and modeling work, and the inferred influence of species interactions on observed metacommunity dynamics was limited. These results suggest that although local interactions among the butterfly, parasitoid, and mildew occur, their roles in metacommunity spatiotemporal dynamics are relatively weak. Instead, all species respond to variation in plant abundance, which may in turn fluctuate in response to variation in climate, land use, or other environmental factors.
Highlights
Species interactions within and among trophic levels are central to the assembly, structure, and dynamics of communities (Paine 1966, Holt 1997, Guzman et al 2019) and, more generally, to the origin and maintenance of biodiversity (Ehrlich and Raven 1964, Stebbins 1970, Estes et al 2011, Janz 2011)
The dynamics of ecological communities are expected to depend in part on species interactions within and among trophic levels, which can be studied by analyzing joint time series of potentially interacting species that share a common habitat network
We detected consistent strong effects of plant abundance on insect and pathogen metapopulation dynamics, which in turn allowed us to obtain reasonably accurate predictions of metacommunity dynamics from models ignoring direct insect–insect and insect–pathogen interactions. Experimental data make it clear that our three focal species are affecting each other at some level (Table 1), these effects do not appear to lead to detectable deviation from expected independent metapopulation dynamics
Summary
Species interactions within and among trophic levels are central to the assembly, structure, and dynamics of communities (Paine 1966, Holt 1997, Guzman et al 2019) and, more generally, to the origin and maintenance of biodiversity (Ehrlich and Raven 1964, Stebbins 1970, Estes et al 2011, Janz 2011). Time-series data on potentially interacting species collected from multiple sites can be used to assess how both spatial and temporal dynamics of species depend on the presence of potentially interacting species (Yackulic et al 2014, Rota et al 2016, Davis et al 2017, Ovaskainen et al 2017a, Dubart et al 2019, Fidino et al 2019) In their long-term study of a native and an invasive snail occupying a network of several hundred ponds in the West Indies, Dubart et al (2019) detected strong effects of patch occupancy by the potential competitor on colonization rates, suggesting reciprocal competitive effects. We combine these two approaches to test whether species interactions leave a detectable signature in metacommunity dynamics
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