Feedback loops between 3D vegetation structure and ecological functions of animals.

Ecosystems function in a series of feedback loops that can change or maintain vegetation structure. Vegetation structure influences the ecological niche space available to animals, shaping many aspects of behaviour and reproduction. In turn, animals perform ecological functions that shape vegetation structure. However, most studies concerning three-dimensional vegetation structure and animal ecology consider only a single direction of this relationship. Here, we review these separate lines of research and integrate them into a unified concept that describes a feedback mechanism. We also show how remote sensing and animal tracking technologies are now available at the global scale to describe feedback loops and their consequences for ecosystem functioning. An improved understanding of how animals interact with vegetation structure in feedback loops is needed to conserve ecosystems that face major disruptions in response to climate and land-use change.

Prosthetic versus native artery inflow for infrainguinal bypass.

BACKGROUND: Infrainguinal bypass performed after previous prosthetic inflow reconstruction offers a choice of where to perform the proximal anastomosis. The hood of a previous inflow bypass might be technically easier to isolate during reoperative surgery. However, the more distal native artery might offer better patency to the outflow revascularization. The purpose of the present study was to compare the outcomes of infrainguinal bypass using the hood of a previous inflow bypass vs the native artery as the inflow source. METHODS: A single vascular group's database was queried for all cases of infrainguinal bypass performed after previous prosthetic inflow bypass to a femoral artery from January 2006 to December 2016. The demographics, indications, operative details, and long-term results were recorded and analyzed. Two groups were compared stratified by the location of the proximal anastomosis for the distal bypass. In one group, the inflow source for the distal bypass was from the hood of a previous inflow graft (prosthetic). In the second group, the distal native arterial tree was used as the inflow source. A subset analysis of the patency of the distal bypass was also performed between the two groups for those in which the previous inflow reconstruction had become occluded. Patency was calculated using the Kaplan-Meier method. RESULTS: A total of 197 patients had undergone infrainguinal bypass after previous inflow bypass from 2006 to 2016. Of the 197 procedures, 59 (30%) had used the hood of the previous bypass as the inflow source (prosthetic group) and 138 (70%) had used the native artery distal to the hood of the inflow bypass as the inflow source (native group). The indications were similar between the two groups. The two groups had a similar proportion of men and a similar incidence of hypertension, hyperlipidemia, coronary artery disease, tobacco use, and renal disease. The previous inflow procedures were also similar between the two groups. The native artery used for the inflow source in the native group was the profunda femoris in 80 (58%), common femoral artery in 51 (37%), and superficial femoral artery in 7 (5.1%). Patency was significantly greater for the native group at 1 year (91% vs 75%; P = .0221). Also, the patency after inflow bypass occlusion significantly favored the native group at 1 year (87% vs 40%; P = .0035). CONCLUSIONS: Infrainguinal bypass performed after previous ipsilateral inflow bypass offers the option of using the hood of the bypass or a native artery as the inflow source. The present study demonstrated greater patency rates when using the distal native artery as the inflow source. The native artery option also offered continued patency when the inflow bypass occluded.

Experimental Evidence for Branch-to-Bird Transfer as a Mechanism for Avian Dispersal of the Hemlock Woolly Adelgid (Hemiptera: Adelgidae).

Birds have long been hypothesized as primary dispersal agents of the hemlock woolly adelgid (Adelges tsugae Annand). Although A. tsugae eggs and mobile first instars (crawlers) have been collected from wild birds, key mechanistic elements necessary for avian dispersal have never been examined. To evaluate the mechanisms of bird-mediated A. tsugae dispersal, we conducted both stationary (i.e., where crawlers must actively disperse) and disturbance (i.e., where crawlers may transfer from substrates due to mechanical abrasion) dispersal trials. For stationary trials, we tested the role of perching duration, ovisac density, and seasonal timing on the rate of crawler transfer to immobile preserved bird mounts at a single site in Connecticut. For disturbance trials, we explored if transfer rates were different when branches were actively brushed against birds. Both stationary and disturbance trials resulted in successful transfers of A. tsugae to bird mounts, with disturbance trials having significantly higher rates of transfers. Crawler counts from stationary trials increased significantly with local ovisac density. Additionally, we found a nonlinear relationship between crawler transfer and experimental week, with crawler transfer highest at the beginning of sampling in May, coinciding with avian spring migration in Connecticut and the emergence of progrediens crawlers, and spiking again near 14 June, when sistens generation crawlers began to emerge. While many aspects of potential avian dispersal of A. tsugae remain unknown, these results suggest that crawler transfer to birds may occur most often when peak crawler emergence coincides with the northward migration of many small passerine bird species.