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Creating a routing backbone is a fundamental problem in both biology and engineering. The routing backbone of the trail networks of arboreal turtle ants (Cephalotes goniodontus) connects many nests and food sources using trail pheromone deposited by ants as they walk. Unlike species that forage on the ground, the trail networks of arboreal ants are constrained by the vegetation. We examined what objectives the trail networks meet by comparing the observed ant trail networks with networks of random, hypothetical trail networks in the same surrounding vegetation and with trails optimized for four objectives: minimizing path length, minimizing average edge length, minimizing number of nodes, and minimizing opportunities to get lost. The ants’ trails minimized path length by minimizing the number of nodes traversed rather than choosing short edges. In addition, the ants’ trails reduced the opportunity for ants to get lost at each node, favoring nodes with 3D configurations most likely to be reinforced by pheromone. Thus, rather than finding the shortest edges, turtle ant trail networks take advantage of natural variation in the environment to favor coherence, keeping the ants together on the trails.

The technique of restoration of populations of land plants is an old one that is well understood by scientists, agronomists, forestry experts, and the general public. However, only recently has attention been turned to restoring underwater areas with socalled seagrasses. From 1947 onwards, attempts have been made to restore suitable marine areas by using important species; however, only very recently (from August 1973) have large-scale restoration projects been undertaken.The efforts that have been made to replant various seagrass species by different techniques are reviewed, but only two seagrasses, Zostera noltii and Thalassia testudinum, have been restored on a large scale. Both of these can be restored successfully; however, the seeding method of Thalassia appears to be the most practical operation of all, and the most potentially valuable for future research into large-scale restoration, as it allows flexibility of location and of depth of transplantation, and involves the minimum of damage to the donor site. It also ensures the most rapid regrowth, besides being in the long run the most economical method yet devised of restoring a seagrass community. An economic model (see Technical Appendix to this paper) and analysis for restoration costs are given and finally a wide range of uses of restoration of such beds of seagrasses are enumerated.

1To create and maintain a backbone routing network is a basic challenge in many engineered and 2 biological systems [1][2][3], from wireless sensor networks and robot swarms to neural circuits 3 and blood circulation. Optimal routing in such networks often seeks to minimize transport 4 delay [4][5][6][7][8], but routing decisions may be influenced by variability in the terrain [9][10][11][12]. Here 5 we find that turtle ants build trail networks that emphasize coherence, keeping the ants together 6 on the trail in a heterogeneous environment, rather than minimizing the distance travelled. The 7 routing backbone of turtle ants (Cephalotes goniodontus), an arboreal species that forages in the 8 1 tree canopy of tropical forests, connects many nests [13][14][15], using trail pheromone that the ants 9 put down continuously, not just on the way back from a food source. Unlike species that forage 10 on the ground, arboreal ants are constrained to travel within the vegetation network of branches 11 and vines. We compared observed turtle ant trails with random, hypothetical trails in the same 12 surrounding vegetation. Strikingly, the trails do not minimize distance travelled, but instead 13 minimize the total number of nodes in the backbone, and favor nodes with 3d configurations 14 that are easily reinforced with pheromone. Thus, rather than forming the shortest paths, turtle 15 ants take advantage of natural variation in the environment to build coherent trails. This ensures 16 that the nests and food sources stay connected, at the expense of longer travel time. This design 17 principle may be beneficial in applications where distributed agents, such as swarms of robots, 18 must coordinate using a communication backbone in complex environments to collectively 19 solve a task, such as building a structure, searching for resources, or surveying terrain [16]. 20 Introduction 21The goal of a backbone routing network is to ensure that there is a path for any two 22 devices on the network to communicate. In real-world systems, however, physical variation in the 23 environment can affect the accuracy and rate of communication [9][10][11][12][17][18][19]. Understanding the 24 physical structure of the environment may improve the design of routing algorithms [16,[20][21][22][23][24], for 25 example, by reducing the search space of possible routing paths and steering network construction 26 away from parts of the terrain that are difficult to reach. 27The 14,000 species of ants have evolved diverse distributed routing and search algorithms to 28 search for, obtain, and distribute resources [25] in the diverse environments that they inhabit [26-29 29]. For example, species such as Formica and Argentine ants, which forage and build trails in 30 a 2d-plane, have minimal constraints on trail geometry [30][31][32], and can minimize the distance 31 travelled by forming trails with branch points that approximate Steiner trees [27, 33, 34], an NP-32 complete generalization of the minimal spanning tree concept. By contrast, many specie...

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