Spatio-temporal variation in foodscapes modifies deer browsing impact on vegetation

Context

Ungulate browsers often alter plant composition and reduce diversity in forests worldwide, yet our ability to predict browse impact on vegetation remains equivocal. Theory suggests, however, that ungulate distribution and foraging impacts are shaped by scale-dependent decisions based on variation in habitat composition and structure encountered within their home range.

Objective

Examine how variation in habitat composition at landscape (259 ha) scales modulates browse impact on vegetation at local scales.

Methods

We measured vegetation richness and abundance in plots with and without white-tailed deer (Odocoileus virginianus) at 23 northern hardwood forest sites distributed across a 6500 km² area in Pennsylvania, USA. Experimental sites were embedded within landscapes with varying levels of habitat composition and deer densities.

Results

Browsing reduced vegetation richness and cover by as much as 53 and 70%, respectively; however, we found browse impact was modulated by variation in the relative abundance of managed habitats that alter forage availability. Specifically, relative to fenced areas, browse impact weakened and ultimately disappeared as the proportion of forage-rich habitats (e.g., recent harvests) increased to ≥20%. Conversely, vegetation grew increasingly depauperate as landscapes contained greater proportions of forage-poor habitats (i.e., older harvests), particularly when browsed.

Conclusions

Our results underscore how management actions that alter forage availability to ungulates throughout the landscape (i.e. the foodscape) can shape forest-ungulate interactions and suggest a new paradigm whereby managers evaluate and undertake actions at the appropriate spatio-temporal scales to proactively limit the deleterious impact of browsing on plant biodiversity.

     

Metabolic responses of juvenile GIFT strain of Nile tilapia (Oreochromis niloticus) to dietary L‐tryptophan supplementation

A 60‐day indoor feeding trial was conducted to evaluate the effects of dietary tryptophan supplementation on growth performances, whole‐body chemical composition, expression of muscle growth‐related genes (MyoD, myogenin and myostatin), and haematological and biochemical responses of juvenile genetically improved farmed tilapia (GIFT). Five corn–soy‐based isonitrogenous and isoenergetic diets were formulated to contain graded levels of dietary tryptophan (2.6, 3.2, 3.7, 4.2 and 4.8 g/kg of diet). Each diet was randomly assigned to triplicate groups of 30 fish (5.3 ± 0.1 g) per experimental unit, which were fed thrice a day (9:00, 13:00 and 17:00 hr). Maximum growth performances and feed utilization were observed in fish fed tryptophan at 3.7 g/kg of diet. There was no significant (p > .05) effect on whole‐body composition and amino acid profile by dietary tryptophan supplementation. However, significant (p < .05) differences were observed in plasma metabolites and the mRNA expression of MyoD, myogenin and myostatin. Serum cortisol level was found significantly lowest in fish fed tryptophan at 3.7 g/kg of diet. Second‐order polynomial regression analysis of weight gain and nitrogen gain against dietary tryptophan levels indicated that the optimum dietary tryptophan requirement for maximum growth and feed utilization of juvenile GIFT tilapia was 3.8 g/kg of diet.     

Exploring uncertainty in population viability analysis and its implications for the conservation of a freshwater fish

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PREFERENCES FOR HEALTH AND ENVIRONMENTAL ATTRIBUTES OF FARMED SALMON AMONGST SOUTHERN ONTARIO SALMON CONSUMERS

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Declines in moose population density at Isle Royle National Park,MI, USA and accompanied changes in landscape patterns

Ungulate herbivores create patterns of forage availability, plant species composition, and soil fertility as they range across large landscapes and consume large quantities of plant material. Over time, herbivore populations fluctuate, producing great potential for spatio-temporal landscape dynamics. In this study, we extend the spatial and temporal extent of a long-term investigation of the relationship of landscape patterns to moose foraging behavior at Isle Royale National Park, MI. We examined how patterns of browse availability and consumption, plant basal area, and soil fertility changed during a recent decline in the moose population. We used geostatistics to examine changes in the nature of spatial patterns in two valleys over 18 years and across short-range and long-range distance scales. Landscape patterns of available and consumed browse changed from either repeated patches or randomly distributed patches in 1988–1992 to random point distributions by 2007 after a recent record high peak followed by a rapid decline in the moose population. Patterns of available and consumed browse became decoupled during the moose population low, which is in contrast to coupled patterns during the earlier high moose population. Distributions of plant basal area and soil nitrogen availability also switched from repeated patches to randomly distributed patches in one valley and to random point distributions in the other valley. Rapid declines in moose population density may release vegetation and soil fertility from browsing pressure and in turn create random landscape patterns.     

Vegetation detection and discrimination within vegetable plasticulture row-middles using a convolutional neural network

Precision Agriculture - Weed control between plastic covered, raised beds in Florida vegetable crops relies predominantly on herbicides. Broadcast applications of post-emergence herbicides are...     

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