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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Facilitation cascade | 2/4 | https://en.wikipedia.org/wiki/Facilitation_cascade | reference | science, encyclopedia | 2026-05-05T07:15:21.359452+00:00 | kb-cron |
=== Transitional (intertidal) === On the cobblestone beaches of New England, cordgrasse ameliorates physical stress for the establishment of ribbed mussels which further facilitating increased diversity within the intertidal ecosystem as secondary foundation species. This is the interaction from which the facilitation cascade concept was formed. This complex habitat has also shown how facilitation cascades can increases invasibility because non-native crabs live on and among ribbed mussels, providing a mechanisms to explain positive relationships between native diversity and invasion success, and the co-existence of native and invasive species through differential use of microhabitats associated with the cascade. In salt marshes, the same species of cordgrass and mussels have also been shown to increase biodiversity, multifunctionality, and resilience to disturbance. Oyster reefs stabilize the intertidal environment by reducing sediment erosion. This enhances growth of marsh grasses which act as secondary foundation species, facilitating invertebrates including bivalves, insects and birds. The places with oyster reefs and intertidal marshes have been observed to support a higher biodiversity and abundance of inhabitants compared to sites inhabited by only one of those foundation species. Mangrove forests along the coast of Australia trap drifting seaweed among their pneumatophores, which this seaweed supports many mollusks through habitat creation and shelter from predation. This example is notable because it involves a foundation species (mangroves) increasing their facilitative effect by aggregating a drifting secondary species from nearby rocky reefs. Another example in transitional environments includes the facilitation of seaweed assemblages in soft-bottom shallow lagoons by gardening tube forming polychaetes that actively incorporate seaweed fragments to reduce predation and increase food-supply. The seaweed subsequently provides habitats and supports the high diversity of small epiphytes, invertebrates, and fish in an otherwise bare soft sediment system. This example is notable because the secondary habitat-forming seaweed is invasive in this region.
=== Terrestrial === A classic example of a terrestrial facilitation cascade includes tropical rainforest trees as the facilitating epiphytes which in turn facilitate the abundance of inhabitant invertebrate species by providing a complex, diverse habitat. For example, about half of the invertebrate biomass and abundance of invertebrates was observed to be dependent on secondary epiphyte habitats, suggesting that early estimates of the notably high arthropod diversity in tropical forests may in part be driven by facilitation cascades. This example is notable due to the different taxonomic composition and larger size of insects found in the secondary, intermediate habitat when compared with that of the primary foundation tree species representing the basal habitat. In temperate forests, a similar cascade unfolds in which facilitation of Spanish moss by oak trees increases invertebrate diversity. In this example, the Spanish moss depend on the oak to reduce physical stress and the invertebrates are reliant on the Spanish moss to increase moisture and lower predation stress. Another terrestrial facilitation cascade includes trees, mistletoe, and birds, where trees are the primary foundation species that facilitates mistletoe, a secondary foundation species, which then facilitates the nesting and feeding of local and migratory birds. This example has been observed in multiple places around the world from pine forests in southeastern Spain to semi-arid southeastern Zimbabwean savannas. The example is notable because mistletoes can be parasitic and have a negative effect on their tree hosts, which is a reminder that the direction and strength of interactions associated with facilitation cascades can be context-dependent.
=== Freshwater === A classic freshwater facilitation cascade includes freshwater plants facilitating growth of algal filaments which in turn facilitate snails. Here, the plants act as primary foundation species, while the algal filaments, attached by plant holdfasts, are secondary foundation species, facilitating the snail inhabitant. This example is significant due to the chemical signals sent from secondary foundation species to attract the diversity of inhabitant snail to the cascade habitat. However, only a few studies appear to have documented freshwater facilitation cascades, and it remains to be determined whether this is a function of the ecosystem structure or simply a reflection of historic research perspectives.
== Scale and ecological feedbacks ==
=== Spatial configuration === The primary and secondary foundation species that make up a facilitation cascade can occur in one of two spatial configurations. First are nested configurations in which the two foundation species are found intermixed or with one facilitator living on another, as in a mangrove pneumatophore providing a surface for oyster colonization. Second are adjacent configurations in which the facilitative species are found segregated across the landscape, as in oyster reefs near salt marshes, or coral reefs adjacent to seagrass. Whether foundation species in a cascade are found in adjacent or nested configurations depends on whether competition for resources at some scale drives one foundation species to displace another. The stress gradient hypothesis has proven useful for predicting which configuration is likely to prevail. In some instances there is scale dependence of the interactions, where competition over short distances leads to zonation of foundation species with distinct borders, and facilitation over longer distances occurs between the organisms in these zones. Facilitation cascades can also be structured as patches on the landscape that arise either because a primary and secondary habitat-forming species co-occur in patches, or a secondary habitat-former exists in patches within a large continuous habitat created by the primary habitat-former.