Ants disperse seeds farther in habitat patches with corridors

Habitat corridors are often used by land managers to restore connectivity to fragmented landscapes. While there is work showing positive impacts of corridors on biodiversity by promoting colonization and dispersal, less is known about how these effects cascade to the interactions between species, including mutualisms.

Burt, M.A., Resasco, J., Haddad, N.M. and Whitehead, S.R. 2022. Ants disperse seeds farther in habitat patches with corridors. Ecosphere 13: e4324.

In our recent study, we investigated the impacts of experimental corridors on seed dispersal mutualisms between ants and the plant Piriqueta cistoides (pitted stripe seed). Ant seed dispersal mutualisms, also known as myrmecochory, occur in plants with seeds that have lipid-rich appendages called elaiosomes.

When the plant’s seeds are ready for dispersal, the ants bring them back to their nests and feed the elaiosomes to their young, typically leaving the seed intact. They then move the seed to trash middens within or outside their nest (on average ~75-100cm away from the parent plant). Thus, the ants benefit from the mutualism by receiving a food reward from the plant, and the plants benefit by having their seeds dispersed away from their parent plants to a nutrient-rich germination site.

Our study took place in the Savannah River Site (SRS) Corridor Experiment in South Carolina. This landscape-scale experiment, which is maintained in collaboration with the USDA Forest Service-Savannah River, compares habitat patches with and without corridors to understand the effects of habitat connectivity and edge amount. Each habitat patch is restored long leaf pine savanna surrounded by loblolly pine plantation.

With this experiment, we investigated the impacts of connectivity and edge effects on ant seed dispersal by observing caches of seeds at both the edge and interior of connected and isolated patches. We recorded the time seeds were moved, how far they were moved, the species of ants that moved the seeds, and the total number of seeds moved at each seed cache.

We observed 11 different species of ants visiting our seed caches, the most common being Solenopsis invicta (red imported fire ants), Crematogaster lineolata (acrobat ants), and Dorymyrmex species (cone ants). We found that, across species, ants moved seeds farther in patches with corridors, but only in the interior portion of patches. In the interior of patches with corridors, ants moved seeds about twice as far as ants in isolated patches.

Although we found this difference in dispersal distance, we did not find any differences in the number of seeds dispersed or the time it took ants to detect seeds. We also did not find any differences in ant community composition visiting seed caches across patch types, suggesting that shifts in ant behavior or other factors increased ant seed dispersal in patches connected by corridors.

Overall, these results indicate a potentially underappreciated mechanism through which corridors may increase plant diversity in fragmented habitats. The dispersal of seeds to greater distances away from the parent plant in connected patches may help mitigate a potentially competitive germination space under the parent plant. Although ants move seeds short distances on average, those dispersal events may accumulate across generations.

State	Year	Policy	Description
New Hampshire	2026	SB592	Enables regional, conservation, and energy resource planning for habitat strongholds and wildlife corridors
New Hampshire	2019	SB200	Requires the New Hampshire Department of Transportation to consider fish and wildlife crossings and mitigation measures in all future road and culvert projects
New Hampshire	2016	SB376	Requires the fish and game department to identify existing and needed wildlife corridors connecting wildlife habitats in the state and to make recommendations for legislative changes

State	Year	Policy	Description
Maine	2023	LD258	Appropriates $7.5 million to Department of Transportation to improve roadways with potential adaptations for wildlife
Maine	2023	LD1881	Establishes compensation fee program relating to fish and wildlife habitats and associated corridors, including compensation paid by solar energy development
Maine	2023	LD508	Requires Department of Environmental Protection to review its permitting laws concerning climate change, habitat connectivity, ecological resilience, and coastal environments

State	Year	Policy	Description
New Jersey	2025	S3618	Directs state agencies to develop a Wildlife Corridor Action Plan
New Jersey	2024	S3916/A5486	Expands eligibility for existing wildlife fencing programs by including farmers leasing farmland
New Jersey	2007	NJAC7:13	Requires the state to incorporate wildlife crossings or a natural bank for terrestrial threatened and endangered species and/or species of concern when a new bridge or culvert project would cause habitat fragmentation

State	Year	Policy	Description
New Mexico	2023	SB72	Appropriates money to new Wildlife Corridors Fund for implementation of wildlife crossing projects under New Mexico Wildlife Corridor Action Plan
New Mexico	2022	HB 2	Allocates funding for projects to reduce wildlife-vehicle collisions and allows the Department of Transportation and Department of Game to implement their Wildlife Corridors Action Plan
New Mexico	2019	SB 228	Requires the creation of a Wildlife Corridor Action Plan that includes comprehensive guidance to agencies for identifying, prioritizing and maintaining important areas for wildlife movement

State	Year	Policy	Description
Washington	2023	HB1216/SB5196	Requires Department of Ecology to prepare environmental impact statements for clean energy projects that consider impacts to habitat connectivity and wildlife migration corridors
Washington	2022	SB5689	Provides funding for US 97 Wildlife Crossing Improvements project
Washington	2019	SEO 1031.02	Recognizes the effect of roadways in creating barriers to wildlife movement, breeding, and migrations; the Washington State Department of Transportation will promote and support Practical Solutions and Planning and Environmental Linkages to integrate habitat connectivity and biodiversity plans; will make use of the highway prioritization map known as Habitat Connectivity Investment Priorities; and will corporate and coordinate with other agencies involved in wildlife habitat protection, specifically along highways

Connecting Science to Conservation

Ants disperse seeds farther in habitat patches with corridors

Burt, M.A., Resasco, J., Haddad, N.M. and Whitehead, S.R. 2022. Ants disperse seeds farther in habitat patches with corridors. Ecosphere 13: e4324.

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About the Author: Melissa Burt

State	Year	Policy	Description
Wyoming	2026	SF0052	Allocates funds for restoration of aquatic habitats including barrier removal for fish
Wyoming	2025	SF0088	Allocates funds for projects improving wildlife connectivity including fence removal, wildlife crossings improvements, and habitat restoration
Wyoming	2024	SF0060	Provides funds to help maintain primary migration corridors for ungulates in the Little Snake River Conservation District
Wyoming	2023	SF0106	Provides funds for large wildlife crossing projects across the state
Wyoming	2022	SF0048	Approves funding for specific wildlife crossings and aquatic connectivity initiatives
Wyoming	2021	SF066	Provides funds for large wildlife crossing projects across the state
Wyoming	2020	EO 1	Designates three mule deer migration corridors and establishes the process whereby future corridors can be designated
Wyoming	2020	HB 69	Establishes a system wherein funding from outdoor recreation can be appropriated for wildlife conservation efforts related to the state’s transportation system
Wyoming	2018	HB39	Proceeds from the newly established wildlife conservation license plates are allocated to wildlife connectivity improvements to the state transportation system

State	Year	Policy	Description
Vermont	2023	Act59	Vermont's 30x30 law that commits to conserving and maintaining an ecologically functional landscape that sustains biodiversity and maintains landscape connectivity
Vermont	2016	Act 171	Primarily focuses on timber harvesting regulations, but calls for a study of necessary revisions to planning statutes that protect contiguous areas of forestland from fragmentation and promote habitat connectivity between forestlands

State	Year	Policy	Description
Colorado	2026	SB141	Creates optional collision prevention fee to fund wildlife safe passage projects
Colorado	2025	HB1093	Restricts local limits on residential density unless offset elsewhere, exempts areas near wildlife crossings, and allows municipalities to seek judicial review of land use initiatives
Colorado	2023	SB 23-092	Encourages minimal impacts to wildlife migration corridors when constructing solar panel farms
Colorado	2023	SB 214	Appropriates funding to the Colorado Wildlife Safe Passages Fund for wildlife crossing projects
Colorado	2022	SB22-151	Creates a $5 million fund for measures that reduce wildlife-vehicle collisions and reconnect habitat fragmented by roads
Colorado	2022	HB22-1072	Expands the scope of Habitat Partnership Program to fund efforts to conserve wildlife migration
Colorado	2021	SJR 21-021	Aims to protect and enhance habitat connectivity in the state through the establishment of a working group to develop state policies on corridors, as well as the commission of a report on state corridors and voluntary policies to support willing landowners in improving connectivity
Colorado	2019	EO 11	Directs Colorado agencies to identify policy, regulatory, and legislative opportunities to ensure the ongoing conservation of seasonal big game habitat and migration corridors
Colorado	2018	SB 18-143	States explicit goals for Division of Parks and Wildlife to invest in habitat conservation and wildlife crossings

State	Year	Policy	Description
California	2026	SB1250	Requires the Department of Transportation (Caltrans) to include wildlife connectivity corridors and needs into its infrastructure project planning
California	2024	AB1889	Requires counties and municipalities to conserve wildlife corridors when planning new developments
California	2023	AB1760	Calls for a statewide analysis of wildlife corridors and connectivity to support conservation planning and climate change adaptation activities.
California	2023	SB145	Outlines provisions for transportation-related environmental mitigation, including funding for wildlife corridors, property and credit purchases for mitigation, reporting requirements, and mandates for wildlife crossings along Interstate 15.
California	2023	SB101	Provides funding for wildlife corridors and open spaces, including projects to improve connectivity and reduce barriers between habitat areas.
California	2022	AB2344	Establishes a state program to address roads with high wildlife-vehicle collisions, authorizes Caltrans to develop standalone wildlife connectivity projects, mandates an inventory and prioritization system for critical areas, and requires integration of wildlife passage features into relevant road designs.
California	2022	AB1384	Requires agencies to address vulnerabilities in Safeguarding California Plans, including protecting and enhancing wildlife corridors
California	2021	SB790	Approves compensatory mitigation credits for wildlife connectivity actions
California	2021	AB1183	Establishes the California Desert Conservation Program to protect biodiversity, including the protection and enhancement of habitat connectivity
California	2021	AB128	Appropriates funding for wildlife crossing projects, including the Liberty Canyon crossing for mountain lions
California	2015	AB 498	Amends the California Fish and Game Code to encourage, wherever feasible, voluntary steps to protect the functioning of wildlife corridors
California	2014	AB1471	Provides funds to the Sacramento- San Joaquin Delta Conservancy, in part to protect and restore aquatic, wetland, and migratory bird ecosystems including corridors.
California	2008	AB2785	Orders Dept. of Fish & Wildlife to investigate, study, and identify key wildlife corridors and linkages within the state, and to make those areas public