Graduate Thesis Or Dissertation
 

Does the Matrix Matter? Using Radio Frequency Identification (RFID) Technology to Examine Hummingbird Movements in Fragmented Tropical Landscapes

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  • There is increasing evidence that the type of land cover surrounding remnant patches of native habitats (the ‘matrix’) can modify effects of landscape change on biodiversity; thus the traditional idea of dichotomous habitat and non-habitat following island biogeography theory is insufficient in complex landscapes. Matrix type can have dramatic influences on the amount of functional connectivity in a landscape, and some types of land use may conserve connectivity better than others. Evidence is accumulating across multiple systems that pollinator communities and the plants they pollinate and depend upon respond negatively to habitat loss and fragmentation. However, relatively little effort has been devoted to examining the effects of matrix type on pollinator movements. Tropical forest conversion often results in matrix areas of agricultural use, predominantly animal pasture and crop growth. Areas of pasture are vastly different than native forest, both in terms of physical structure and the resources they might provide to native pollinators. Our research compared responses of four mature-forest associated tropical hummingbird species to varying matrix type. We conducted a titration experiment where unlimited food was provided along transects through two matrix types (pasture and regenerating forest (hereafter “scrub”) to test whether functional connectivity differed, independent of resource availability. We used radio frequency identification (RFID) systems to empirically test differences in the use of matrix types by species, as well as the distance each species ventured into each matrix type. The number of feeder visits for one specialist species, the green hermit (Phaethornis guy), was strongly influenced by matrix type; scrub was >1.4 times (95% CI = 1.24 – 1.57) more permeable than pasture, and forest was >4 times (95% confidence interval [CI] = 3.66 – 4.65) more permeable than scrub. However, we did not detect an effect of matrix type on the number of rufous-tailed hummingbird (Amazilia tzacatl) visits. The other two species (violet sabrewing [Campylopterus hemileucurus] and stripe-throated hermit [Phaethornis striigularis]) were never detected in pasture, and only rarely in scrub, although sample sizes for these species were low. Interestingly, two of our species – violet sabrewing and green hermit – also showed a strong affinity for forest interior, which may explain greater observed rates of pollination in large patches. Overall, our results suggest that the presence regenerating tropical forest scrub boosts functional connectivity by a ‘forest interior’ species (the green hermit), and therefore has the potential to restore hummingbird pollination networks in fragmented tropical landscapes.
  • Keywords: landscape, violet sabrewing, RFID, green hermit, Costa Rica, radio frequency identification, rufous-tailed hummingbird, matrix, hummingbird
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