Regulation and acclimation of leaf gas exchange in a piñon–juniper woodland exposed to three different precipitation regimes

Leaf gas‐exchange regulation plays a central role in the ability of trees to survive drought, but forecasting the future response of gas exchange to prolonged drought is hampered by our lack of knowledge regarding potential acclimation. To investigate whether leaf gas‐exchange rates and sensitivity to drought acclimate to precipitation regimes, we measured the seasonal variations of leaf gas exchange in a mature piñon–juniper Pinus edulis–Juniperus monosperma woodland after 3 years of precipitation manipulation. We compared trees receiving ambient precipitation with those in an irrigated treatment (+30% of ambient precipitation) and a partial rainfall exclusion (?45%). Treatments significantly affected leaf water potential, stomatal conductance and photosynthesis for both isohydric piñon and anisohydric juniper. Leaf gas exchange acclimated to the precipitation regimes in both species. Maximum gas‐exchange rates under well‐watered conditions, leaf‐specific hydraulic conductance and leaf water potential at zero photosynthetic assimilation all decreased with decreasing precipitation. Despite their distinct drought resistance and stomatal regulation strategies, both species experienced hydraulic limitation on leaf gas exchange when precipitation decreased, leading to an intraspecific trade‐off between maximum photosynthetic assimilation and resistance of photosynthesis to drought. This response will be most detrimental to the carbon balance of piñon under predicted increases in aridity in the southwestern USA.     

Dissolved carbon leaching from soil is a crucial component of the net ecosystem carbon balance

Estimates of carbon leaching losses from different land use systems are few and their contribution to the net ecosystem carbon balance is uncertain. We investigated leaching of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and dissolved methane (CH₄), at forests, grasslands, and croplands across Europe. Biogenic contributions to DIC were estimated by means of its δ¹³C signature. Leaching of biogenic DIC was 8.3±4.9 g m^?2 yr^?1 for forests, 24.1±7.2 g m^?2 yr^?1 for grasslands, and 14.6±4.8 g m^?2 yr^?1 for croplands. DOC leaching equalled 3.5±1.3 g m^?2 yr^?1 for forests, 5.3±2.0 g m^?2 yr^?1 for grasslands, and 4.1±1.3 g m^?2 yr^?1 for croplands. The average flux of total biogenic carbon across land use systems was 19.4±4.0 g C m^?2 yr^?1. Production of DOC in topsoils was positively related to their C/N ratio and DOC retention in subsoils was inversely related to the ratio of organic carbon to iron plus aluminium (hydr)oxides. Partial pressures of CO₂ in soil air and soil pH determined DIC concentrations and fluxes, but soil solutions were often supersaturated with DIC relative to soil air CO₂. Leaching losses of biogenic carbon (DOC plus biogenic DIC) from grasslands equalled 5–98% (median: 22%) of net ecosystem exchange (NEE) plus carbon inputs with fertilization minus carbon removal with harvest. Carbon leaching increased the net losses from cropland soils by 24–105% (median: 25%). For the majority of forest sites, leaching hardly affected actual net ecosystem carbon balances because of the small solubility of CO₂ in acidic forest soil solutions and large NEE. Leaching of CH₄ proved to be insignificant compared with other fluxes of carbon. Overall, our results show that leaching losses are particularly important for the carbon balance of agricultural systems.     

Using Patterns in Track-Plate Footprints to Identify Individual Fishers

Abstract: If individuals can be identified from patterns in their footprints, noninvasive survey methods can be used to estimate abundance. Track plates capture fine detail in the footprints of fishers (Martes pennanti), recording rows of dots corresponding to tiny papillae on the animal's metacarpal pad. We show that the pattern of these dots can be used to identify individual fishers, similar to human fingerprints. A probabilistic model of uniqueness based on variation in spacing between 1,400 pairs of dots that we measured in prints of 14 different fisher feet suggests the probability of encountering a similar pattern in the print of a different foot by chance alone is ≤ 0.35ⁿ, where n = the number of dot pairs examined. This predicts a 0.00003 probability that a match made using 10 pairs of dots is false. Dot spacing from footprints made by the same foot was remarkably consistent (sN = 0.02 mm, n = 24 dot pairs). Combined, these results suggest dot patterns in fisher footprints were unique to individuals and were consistently reproduced on track plates. Empirical tests of matching accuracy were best with good-quality prints, highlighting the need for experience judging when prints are usable. We applied print matching to fisher detections collected on track plates deployed at 500-m intervals along 10 3.5-km transects in the Adirondack region of New York, USA. Of 62 fisher detections, 85% had ≥ 1 footprint of suitable quality to compare with other high-quality prints. We found that most detections from a transect were from the same individual fisher suggesting nonindependence of detections. Thus, data from traditional track-plate deployments over small time periods cannot be used as a measure of abundance, but new study designs using print matching could obtain robust noninvasive, mark—recapture density estimates.     

Are dingoes a trophic regulator in arid Australia? A comparison of mammal communities on either side of the dingo fence

The direct and indirect interactions that large mammalian carnivores have with other species can have far‐reaching effects on ecosystems. In recent years there has been growing interest in the role that Australia's largest terrestrial predator, the dingo, may have in structuring ecosystems. In this study we investigate the effect of dingo exclusion on mammal communities, by comparing mammal assemblages where dingoes were present and absent. The study was replicated at three locations spanning 300 km in the Strzelecki Desert. We hypothesized that larger species of mammal subject to direct interactions with dingoes should increase in abundance in the absence of dingoes while smaller species subject to predation by mesopredators should decrease in abundance because of increased mesopredator impact. There were stark differences in mammal assemblages on either side of the dingo fence and the effect of dingoes appeared to scale with body size. Kangaroos and red foxes were more abundant in the absence of dingoes while Rabbits and the Dusky Hopping‐mouse Notomys fuscus were less abundant where dingoes were absent, suggesting that they may benefit from lower red fox numbers in the presence of dingoes. Feral cats and dunnarts (Sminthopsis spp.) did not respond to dingo exclusion. Our study provides evidence that dingoes do structure mammal communities in arid Australia; however, dingo exclusion is also associated with a suite of land use factors, including sheep grazing and kangaroo harvesting that may also be expected to influence kangaroo and red fox populations. Maintaining or restoring populations of dingoes may be useful strategies to mitigate the impacts of mesopredators and overgrazing by herbivores.     

The use of habitat mosaics by terrestrial vertebrate fauna: implications for conservation and management

Many species of vertebrates require multiple habitats to obtain different resources at different stages of their life-cycles. Use of habitat mosaics takes place on a variety of spatial and temporal scales, from a daily requirement for adjacent habitats to seasonal use of geographically separated environments. Mosaics of habitats are also required in some species to allow ontogenetic habitat shifts, while in others each sex may have specific requirements that are met by different habitats. The extent and nature of animal movements are key (but generally poorly known) factors affecting the vulnerability of species to landscape change. The requirement by many species for multiple habitats suggests that their conservation will be most effective in a mosaic environment and that protection of certain high profile habitats alone, such as rainforest, will be insufficient to achieve conservation goals. Management regimes that result in homogenization of habitats should be avoided. Priority should be given to research that identifies the extent to which species can locate habitat mosaics, at different spatial scales and arrangements, in modified environments.     

Complex effects of habitat loss on Golden Eagles Aquila chrysaetos

The development of commercial forests presents potential threats to large raptors that rely on prey caught in open country. We examined the effect of afforestation of breeding habitat used by a population of Golden Eagles Aquila chrysaetos in Scotland where, over the last 50 years, extensive stands of exotic conifers have been planted. Using data for 31 years on territory occupancy and breeding success, together with spatiotemporally dynamic mapping of forest cover and predicted areas of territory‐use in a Geographical Information System, we examined relationships between forest cover and Eagle ecology at landscape and individual territory scales. Several territories were abandoned during the earliest phases of forest planting, but relatively few were apparently lost to later plantings. Territories with poorer breeding productivity appeared to be more vulnerable to abandonment than territories with better breeding productivity. At the landscape scale, temporal differences in breeding productivity were negatively related to the extent of forest cover, although productivity of individual territories showed no clear relationship with forest cover. Several territories with less than a 5% increase in forest cover experienced reduced productivity; however, territories least constrained by neighbouring pairs of Eagles showed an increase in productivity. Territories experiencing the greatest increases in forest cover showed a greater use of spatially separated nest‐sites by occupying pairs. Hence, pairs that were less constrained by neighbours appeared to compensate for loss of open habitat by shifting their territory‐use, whereas pairs that were more constrained could not compensate for open habitat loss and suffered reduced productivity (and, probably in some cases, abandoned the territory). We suggest that simple guidelines based on the extent and locations of habitat loss are inadequate when predicting effects on large territorial raptors such as Golden Eagles. Consideration should also be given to the ‘quality’ of a territory or occupying pair, as well as the extent to which territory‐use is constrained by neighbouring pairs or other ‘unsuitable habitat’ which may have been affected by previous episodes of open habitat loss.     

Stream community structure in relation to spatial and temporal variation: a habitat templet study of two contrasting New Zealand streams

• 1 The physical characteristics of two contrasting streams, and habitat types within these streams, are described in terms of a two-dimensional physical habitat templet in which disturbance frequency and the availability of spatial refugia are the temporal and spatial axes.
• 2 It is predicted that habitats experiencing a high disturbance frequency and low refuge availability will be characterized by a low invertebrate species diversity, a low biomass of epilithic algae and particulate organic matter and a community made up of mobile, weedy species. Habitats having a low disturbance frequency and high refuge availability will be characterized by a diverse community containing sedentary and specialist species, with high algal and particulate organic matter levels.
• 3 A lower median substrate particle size and higher shear stress regime in Timber Creek were indicative of a higher disturbance frequency than in the Kyeburn. Substrate diversity was lower in Timber Creek than in the Kyeburn and indicated that the availability of refugia was lower in Timber Creek. In both streams, pools were found to have a higher disturbance frequency and lower availability of refugia than riffles.
• 4 Invertebrate species diversity, the biomass of epilithic algae and particulate organic matter and the representation of sedentary species, filter feeders and shredders were higher in the more temporally stable and spatially heterogeneous Kyeburn. The community of Timber Creek, frequently disturbed and having low refuge availability, had a high proportion of mobile and weedy species, with the highly mobile, generalist-feeding Deleatidium spp. (Ephemeroptera; Leptophlebiidae) being the most dominant organisms.
• 5 The predictions made about stream community structure and species characteristics in relation to disturbance frequency and the availability of spatial refugia are generally supported. Now a larger scale investigation is required to test the generality of the predictions. We conclude that the habitat templet approach offers a sound framework within which to pose questions in stream ecology.

     

Selection of habitat components by two species of agamid lizards in sandridge desert,central Australia

Abstract We studied the use and selection of habitat components by two species of agamid (dragon) lizards in the Simpson Desert, Queensland, Australia. Both the military dragon (Ctenophorus isolepis) and central netted dragon (Ctenophorus nuchalis) were captured in pitfall traps surrounded by areas of open sand, but the mean coverage of spinifex (Triodia basedowii) was greater (35%) around traps capturing C. isolepis than around those capturing its congener (approx. 8%). Direct observations of free‐ranging lizards confirmed that C. isolepis spent most time in, or within 30 cm of, spinifex hummocks, whereas C. nuchalis primarily perched in dead wood. Both species spent most (≥75%) of the time they were observed at rest, with little time spent feeding or moving. Ctenophorus isolepis spent 67% of its time in shade and was active in temperatures between 37.5°C and 43.3°C, whereas C. nuchalis spent 81% of its time in open sun and was active between 35.9°C and 48.1°C. Transect surveys at observation sites showed that open sand was the dominant habitat component available to both species. However, sand was under‐used compared with its availability. Ctenophorus isolepis instead showed strong selection for spinifex cover and C. nuchalis for dead wood; shrub cover was little used. We discuss several mechanisms that may drive the observed pattern of habitat selection, but cannot specify which is the most important. However, the results indicate clear partitioning of habitat between the two species, and suggest that this segregation may facilitate coexistence at local and regional scales.