Understanding the mechanisms of spatial variation of biological invasions, across local‐to‐global scales, has been a major challenge. The importance of evolutionary history for invasion dynamics was noted by Darwin, and several studies have since considered how biodiversity of source and recipient regions can influence the probability of invasions. For over a century, the Panama Canal has connected water bodies and biotas with different evolutionary histories, and created a global shipping hot spot, providing unique opportunities to test mechanisms that affect invasion patterns. Here, we test for asymmetry in both the extent of invasions and predation effects, a possible mechanism of biotic resistance, between two tropical oceans at similar latitudes. We estimated nonnative species (NNS) richness for sessile marine invertebrates, using standardized field surveys and literature synthesis, to examine whether invasions are asymmetrical, with more NNS present in the less diverse Pacific compared to the Atlantic. We also experimentally tested whether predation differentially limits the abundance and distribution of these invertebrates between oceans. In standardized surveys, observed total NNS richness was higher in the Pacific (18 NNS, 30% of all Pacific species) than the Atlantic (11 NNS, 13% of all Atlantic species). Similarly, literature‐based records also display this asymmetry between coasts. When considering only the reciprocal exchange of NNS between Atlantic and Pacific biotas, NNS exchange from Atlantic to Pacific was eightfold higher than the opposite direction, exceeding the asymmetry predicted by random exchange based simply on differences of overall diversity per region. Predation substantially reduced biomass and changed NNS composition in the Pacific, but no such effects were detected on the Atlantic coast. Specifically, some dominant NNS were particularly susceptible to predation in the Pacific, supporting the hypothesis that predation may reduce the abundance of certain NNS here. These results are consistent with predictions that high diversity in source regions, and species interactions in recipient regions, shape marine invasion patterns. Our comparisons and experiments across two tropical ocean basins, suggest that global invasion dynamics are likely driven by both ecological and evolutionary factors that shape susceptibility to and directionality of invasions across biogeographic scales.
The hypothesis that biotic interactions are stronger at lower relative to higher latitudes has a rich history, drawing from ecological and evolutionary theory. While this hypothesis suggests that stronger interactions at lower latitudes may contribute to the maintenance of contemporary patterns of diversity, there remain few standardized biogeographic comparisons of community effects of species interactions. Using marine seagrasses as a focal ecosystem of conservation importance and sessile marine invertebrates as model prey, we tested the hypothesis that predation is stronger at lower latitudes and can shape contemporary patterns of prey diversity. To further advance understanding beyond prior studies, we also explored mechanisms that likely underlie a change in interaction outcomes with latitude. Multiple observational and experimental approaches were employed to test for effects of predators, and the mechanisms that may underlie these effects, in seagrass ecosystems of the western Atlantic Ocean spanning 30° of latitude from the temperate zone to the tropics. In predator exclusion experiments conducted in a temperate and a tropical region, predation decreased sessile invertebrate abundance, richness and diversity on both natural and standardized artificial seagrass at tropical but not temperate sites. Further, predation reduced invertebrate richness at both local and regional scales in the tropics. Additional experiments demonstrated that predation reduced invertebrate recruitment in the tropics but not the temperate zone. Finally, direct observations of predators showed higher but variable consumption rates on invertebrates at tropical relative to temperate latitudes. Together, these results demonstrate that strong predation in the tropics can have consequential impacts on prey communities through discrete effects on early life stages as well as longer‐term cumulative effects on community structure and diversity. Our detailed experiments also provide some of the first data linking large‐scale biogeographic patterns, community‐scale interaction outcomes and direct observation of predators in the temperate zone and tropics. Therefore, our results support the hypothesis that predation is stronger in the tropics, but also elucidate some of the causes and consequences of this variation in shaping contemporary patterns of diversity.
- NSF-PAR ID:
- 10458776
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Animal Ecology
- Volume:
- 89
- Issue:
- 2
- ISSN:
- 0021-8790
- Page Range / eLocation ID:
- p. 323-333
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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