Though landscape corridors increase dispersal of many animals and plants, it remains unknown whether increased dispersal increases colonization and establishment of new populations in connected fragments. Working in experimentally fragmented landscapes, we tested how two aspects of habitat fragments altered by corridors- connectivity and edge-to-area ratio- determine patterns of colonization by a solitary, cavity-nesting bee (Megachile rotundata). We found that though higher connectivity initially increased rates of nest-site occupation, higher edge-to-area ratio ultimately increased patch occupation and nest building, likely due to habitat selection by our focal species. Bee colonization was also higher in patches with higher abundances of their preferred food resources, flowers from the Fabaceae family. Our results show the importance of considering the effects of both connectivity and edge on population dynamics in habitat-based conservation in fragmented landscapes.

See manuscript (Griffin & Haddad 2021) for full methods.

Dataset description:

Alfalfa leaf-cutting bee (Megachile rotundata) colonization of nest boxes across experimental landscapes in the Savanna River Site Corridor Project (Savannah River Site, South Carolina). Each row in the dataset represents counts of nesting bees, nests, and brood cells for each nest box within each habitat patch. Associated floral data was calculated at the patch level, not at the level of individual nest boxes, such that all rows for nestboxes within a given patch have identical values for each floral variable.

Fields

block: each block represents a single experimental landscape, each containing one center patch and 4 peripheral patches varying in shape and connectivity. Blocks were named by number (e.g. Block 8, Block 10 etc.).

patch: There were four peripheral patches per block, named B-D depending on position. All patches were equally sized. B patches were always connected to the center patch by a landscape corridor.

shape: Peripheral patches differed by shape. Shapes included “connected” (patches connected to the center patch by a landscape corridor), “winged” (unconnected patches with habitat with linear elements called pseudocorridors), and “rectangular” (unconnected patches that were rectangular in shape.

connectivity: Peripheral patches differed by connectivity. “connected” patches were connected to the center patch by a landscape corridor, while unconnected patches were not connected to the center patch.

nest_box: We placed 4 nest boxes per patch, for a total of 16 nest boxes per experimental landscape. Boxes were named 1-4 depending on location within the patch, with the two boxes furthest from the center patch labeled 1 and 2 (left to right) and the two boxes closest to the center patch labeled 3 and 4 (left to right).

round1_sample_date: we visited all nestboxes ~10 days following field release to count the number of nesting female bees. Round1_sample_date is the date of that visit (mm/dd/yyyy).

round1_sample_time: the time at which we started our visit of each block for round 1.

Mrotundata_individuals_round1: the number of nesting Megachile rotundata females counted within each nestbox during sampling round 1.

Mrotundata_nests: the final number of nests produced by nesting Megachile rotundata females, counted after all nest boxes and nesting materials were removed from the field.

Mrotundata_cells: the final number of brood cells produced in each nest box, summed across all nests within a box.

flowers_round1: the total number of non-Fabaceae flowers counted within a patch during round 1 of floral sampling (conducted between 25-29^th of May, 2017). All nestboxes within a patch have identical values for this field.

flowers_round2: the total number of non-Fabaceae flowers counted within a patch during round 2 of floral sampling (conducted between 10-13^th of June, 2017). All nestboxes within a patch have identical values for this field.

flowers_bothrounds: the non-Fabaceae flowers of both rounds, summed for each patch. All nestboxes within a patch have identical values for this field.

fabaceae_round1: the total number of Fabaceae flowers counted within a patch during round 1 of floral sampling (conducted between 25-29^th of May, 2017). All nestboxes within a patch have identical values for this field.

fabaceae_round2: the total number of Fabaceae flowers counted within a patch during round 2 of floral sampling (conducted between 10-13^th of June, 2017). All nestboxes within a patch have identical values for this field.

fabaceae_bothrounds: the Fabaceae flowers of both rounds, summed for each patch. All nestboxes within a patch have identical values for this field.