The role of landscape composition and disturbance type in mediating salt marsh resilience to feral hog invasion

The Boar War: Five Hot Factors Unleashing Boar Expansion and Related Emergency

The recent and ever-growing problem of boar (Sus scrofa forms including wild boar, hybrid and feral pig) expansion is a very complex issue in wildlife management. The damages caused to biodiversity and the economies are addressed in different ways by the various countries, but research is needed to shed light on the causal factors of this emergency before defining a useful collaborative management policy. In this review, we screened more than 280 references published between 1975–2022, identifying and dealing with five hot factors (climate change, human induced habitat modifications, predator regulation on the prey, hybridization with domestic forms, and transfaunation) that could account for the boar expansion and its niche invasion. We also discuss some issues arising from this boar emergency, such as epizootic and zoonotic diseases or the depression of biodiversity. Finally, we provide new insights for the research and the development of management policies.

Feral hogs control brackish marsh plant communities over time

Feral hogs modify ecosystems by consuming native species and altering habitat structure. These invasions can generate fundamentally different post-invasion habitats when disturbance changes community structure, ecosystem function, or recovery dynamics. Here, we use multiple three-year exclusion experiments to describe how feral hogs affect hyper-productive brackish marshes over time. We find that infrequent yet consistent hog foraging and trampling suppresses dominant plants by generating a perpetually disturbed habitat that favors competitively inferior species and disallows full vegetative recovery over time. Along borders between plant monocultures, trampling destroys dominant graminoids responsible for most aboveground marsh biomass while competitively inferior plants increase fivefold. Hog activities shift the brackish marsh disturbance regime from pulse to press, which changes the plant community: competitively inferior plants increase coverage, species diversity is doubled, and live cover is lowered by 30% as large plants are unable to take hold in hog-disturbed areas. Release from disturbance does not result in complete recovery (i.e., dominant plant monocultures) because hog consumer control is a combination of both top-down control and broader engineering effects. These results highlight how habitats are susceptible to invasive effects outside of structural destruction alone, especially if large consumers are pervasive over time and change the dynamics that sustain recovery.

A large invasive consumer reduces coastal ecosystem resilience by disabling positive species interactions

Invasive consumers can cause extensive ecological damage to native communities but effects on ecosystem resilience are less understood. Here, we use drone surveys, manipulative experiments, and mathematical models to show how feral hogs reduce resilience in southeastern US salt marshes by dismantling an essential marsh cordgrass-ribbed mussel mutualism. Mussels usually double plant growth and enhance marsh resilience to extreme drought but, when hogs invade, switch from being essential for plant survival to a liability; hogs selectively forage in mussel-rich areas leading to a 50% reduction in plant biomass and slower post-drought recovery rate. Hogs increase habitat fragmentation across landscapes by maintaining large, disturbed areas through trampling of cordgrass during targeted mussel consumption. Experiments and climate-disturbance recovery models show trampling alone slows marsh recovery by 3x while focused mussel predation creates marshes that may never recover from large-scale disturbances without hog eradication. Our work highlights that an invasive consumer can reshape ecosystems not just via competition and predation, but by disrupting key, positive species interactions that underlie resilience to climatic disturbances.