Monitoring an invasive perennial at the landscape scale with remote sensing

Summary   Worldwide, invasive weeds threaten agricultural, natural and urban ecosystems. In Australia's agricultural and grazing regions, invasive species often establish across extensive areas where weed management is hampered by an inability to detect the location and timing of an outbreak. In these vast landscapes, an effective detection and monitoring system is required to delineate the extent of the invasion and identify spatial and temporal factors associated with weed establishment and thickening. In this study, we utilize a time series of remote sensing imagery to detect the spatial and temporal patterns of Prickly Acacia ( Acacia nilotica ) invasion in the Mitchell grass plains of North Queensland. We develop a spectral index from Landsat images which is applied to images from 1989 to 2004, in combination with a classification mask, to identify locations and monitor changes in Prickly Acacia density across 29 000 km² of Mitchell grass plains. The approach identified spectral and temporal signatures consistent with Prickly Acacia infestation on 1.9% of this landscape. Field checking of results confirmed presence of the weed in previously unrecorded locations. The approach may be used to evaluate future spread, or outcomes of management strategies for Prickly Acacia in this landscape and could be employed to detect and monitor invasions in other extensive landscapes.     

Planting methods matter for cost‐effective rainforest restoration

Forest restoration efforts in Australia's Wet Tropics establish <100 ha/year, compared with 20‐year average clearing rates of 1661 ha/year. Establishment costs are serious impediments to restoration efforts. Costs range from $25,000 to $67,000/ha, compared with less than $5,000/ha in other areas using other methods. Some of this difference stems from methods used to plant trees. Augered holes are used commonly in environmental plantings, whereas planting spades are used mostly in forestry plantings. To determine the most cost‐effective planting method between auger and spade planting methods, we compared the planting costs and the survival and growth of seedlings of local rainforest species, The speed of planting with a spade is on average four times quicker than with an auger, whereas the survival (range = 89–94%, spade vs auger respectively), and growth (slightly greater height growth for auger planted individuals) rates were only marginally different. Given these results, using planting spades is a cost‐effective alternative to augering holes.     

Male nest building but not display behaviour directly influences mating success in the polygynous Red Bishop,Euplectes orix

Previous studies of the highly polygynous and strikingly sexually dimorphic Red Bishop, Euplectes orix (Ploceinae, weaverbirds), have suggested random female settlement patterns and no correlates of male reproductive success except the number of nest frames (‘cock's nests’) built by the male. Although this confirms the central role of the nest in weaverbird courtship it also contrasts with demonstrated sexual selection on male morphology and behaviour in several closely related Euplectes species. Two major aspects of male sexual advertising have not been included in previous studies; display behaviour and territory size. In this study we use multivariate selection analysis, with the number of active nests in a territory as the fitness measure, to identify direct and indirect sexual selection on male sexual behaviour, territory size and nest building. In accor–dance with previous findings, mating success was not strongly skewed among the territorial males, and females appeared to settle randomly with respect to available nests. The number of cock𠀧s nest built was the only determinant of male breeding success, even when controlling for male display activity and territory size. We argue that, despite their conspicuous sexual dimorphism, females settle independently of both male or territory quality, and that variance in male reproductive success is a consequence of male–male competition.     

Recovery of tree and mammal communities during large‐scale forest regeneration in Kibale National Park,Uganda

Tropical landscapes are changing rapidly as a result of human modifications; however, despite increasing deforestation, human population growth, and the need for more agricultural land, deforestation rates have exceeded the rate at which land is converted to cropland or pasture. For deforested lands to have conservation value requires an understanding of regeneration rates of vegetation, the rates at which animals colonize and grow in regenerating areas, and the nature of interactions between plants and animals in the specific region. Here, we present data on forest regeneration and animal abundance at four regenerating sites that had reached the stage of closed canopy forest where the average dbh of the trees was 17 cm. Overall, 20.3 percent of stems were wind‐dispersed species and 79.7 percent were animal‐dispersed species, while in the old‐growth forest 17.3 percent of the stems were wind‐dispersed species. The regenerating forest supported a substantial primate population and encounter rate (groups per km walked) in the regenerating sites was high compared to the neighboring old‐growth forests. By monitoring elephant tracks for 10 yr, we demonstrated that elephant numbers increased steadily over time, but they increased dramatically since 2004. In general, the richness of the mammal community detected by sight, tracks, feces, and/or camera traps, was high in regenerating forests compared to that documented for the national park. We conclude that in Africa, a continent that has seen dramatic declines in the area of old‐growth forest, there is ample opportunity to reclaim degraded areas and quickly restore substantial animal populations.     

Human-Imposed,Fine-Grained Patch Burning Explains the Population Stability of a Fire-Sensitive Conifer in a Frequently Burnt Northern Australia Savanna

Woody plant demographics provide important insight into ecosystem state-shifts in response to changing fire regimes. In Australian tropical savannas, the switch from patchy landscape burning by Aborigines to unmanaged wildfires within the past century has been implicated in biodiversity declines including the fire-sensitive conifer, Callitris intratropica. C. intratropica commonly forms small, closed-canopy groves that exclude fire and allow recruitment of conspecifics and other fire-sensitive woody plants. C. intratropica groves provide a useful indicator of heterogeneity and fire regime change, but the mechanisms driving the species’ persistence and decline remain poorly understood. We examined the hypothesis that C. intratropica population stability depends upon a regime of frequent, low-intensity fires maintained by Aboriginal management. We combined integral projection models of C. intratropica population behaviour with an environmental state change matrix to examine how vital rates, grove dynamics and the frequency of high- and low-intensity fires contribute to population stability. Closed-canopy C. intratropica groves contributed disproportionately to population growth by promoting recruitment, whereas singleton trees accounted for a larger proportion of adult mortality. Our patch-based population model predicted population declines under current fire frequencies and that the recruitment of new groves plays a critical role in the species’ persistence. Our results also indicated that reducing fire intensity, a key outcome of Aboriginal burning, leads to C. intratropica population persistence even at high fire frequencies. These findings provide insight into the relationship between ecosystem composition and human–fire interactions and the role of fire management in sustaining the mosaics that comprise ‘natural’ systems.     

Mutations that confer resistance to 2-deoxyglucose reduce the specific activity of hexokinase from Myxococcus xanthus

The glucose analog 2-deoxyglucose (2dGlc) inhibits the growth and multicellular development of Myxococcus xanthus. Mutants of M. xanthus resistant to 2dGlc, designated hex mutants, arise at a low spontaneous frequency. Expression of the Escherichia coli glk (glucokinase) gene in M. xanthus hex mutants restores 2dGlc sensitivity, suggesting that these mutants arise upon the loss of a soluble hexokinase function that phosphorylates 2dGlc to form the toxic intermediate, 2-deoxyglucose-6-phosphate. Enzyme assays of M. xanthus extracts reveal a soluble hexokinase (ATP:D-hexose-6-phosphotransferase; EC 2.7.1.1) activity but no phosphotransferase system activities. The hex mutants have lower levels of hexokinase activities than the wild type, and the levels of hexokinase activity exhibited by the hex mutants are inversely correlated with the ability of 2dGlc to inhibit their growth and sporulation. Both 2dGlc and N-acetylglucosamine act as inhibitors of glucose turnover by the M. xanthus hexokinase in vitro, consistent with the finding that glucose and N-acetylglucosamine can antagonize the toxic effects of 2dGlc in vivo.     

Confirmation of pleisiomorphic daily torpor in mammals: the round-eared elephant shrew Macroscelides proboscideus (Macroscelidea)

The characteristics of daily torpor were measured in the round-eared elephant shrew Macroscelides proboscideus (Macroscelidea) in response to ambient temperature and food deprivation. Elephant shrews are an ancient mammal order within a superordinal African clade including hyraxes, elephants, dugongs and the aardvark. M. proboscideus only employed torpor when deprived of food; torpor did not occur under an ad libitum diet at ambient temperatures of 10, 15 and 25?°C. Torpor bout duration ranged from <1?h to ca. 18?h. The times of entry into torpor were restricted to the scotophase, despite normothermic body temperature patterns indicating a rest phase coincident with the photophase. Full arousal was always achieved within the first 3?h of the photophase. When food deprived, the onset of the rest phase, and hence torpor, advanced with respect to the experimental photoperiod. The lowest torpor body temperature measured was 9.41?°C. Daily torpor in M. proboscideus confirms a pleisiomorphic origin of daily heterothermy. Torpor facilitates risk-averse foraging behaviour in these small omnivores by overcoming long-term energy shortfalls generated by the inherent variability of food availability in their semi-arid, El Niño-afflicted habitats.     

Gastrointestinal parasites of the Samango monkey,Cercopithecus mitis,in Natal,South Africa

Eight gastro-intestinal tracts of Cercopithecus mitis labiatus from Karkloof, Natal, and 121 fecal samples from C. m. erythrarchus from Cape Vidal, Natal, were examined for helminth parasites and/or their eggs. Fecal samples from six of the C. m. labiatus were examined for protozoan cysts. Five protozoon and six helminth species were identified from C.m labiatus. Most adult worms occurred in the caecum and colon, gut regions which also contained the highest volatile fatty acid levels. The eggs of nine helminth species were recovered from C. m. erythrarchus fecal samples; protozoans were not looked for in these samples.     

Correlates of Recent Declines of Rodents in Northern and Southern Australia: Habitat Structure Is Critical

Australia has experienced dramatic declines and extinctions of its native rodent species over the last 200 years, particularly in southern Australia. In the tropical savanna of northern Australia significant declines have occurred only in recent decades. The later onset of these declines suggests that the causes may differ from earlier declines in the south. We examine potential regional effects (northern versus southern Australia) on biological and ecological correlates of range decline in Australian rodents. We demonstrate that rodent declines have been greater in the south than in the tropical north, are strongly influenced by phylogeny, and are consistently greater for species inhabiting relatively open or sparsely vegetated habitat. Unlike in marsupials, where some species have much larger body size than rodents, body mass was not an important predictor of decline in rodents. All Australian rodent species are within the prey-size range of cats (throughout the continent) and red foxes (in the south). Contrary to the hypothesis that mammal declines are related directly to ecosystem productivity (annual rainfall), our results are consistent with the hypothesis that disturbances such as fire and grazing, which occur in non-rainforest habitats and remove cover used by rodents for shelter, nesting and foraging, increase predation risk. We agree with calls to introduce conservation management that limits the size and intensity of fires, increases fire patchiness and reduces grazing impacts at ecological scales appropriate for rodents. Controlling feral predators, even creating predator-free reserves in relatively sparsely-vegetated habitats, is urgently required to ensure the survival of rodent species, particularly in northern Australia where declines are not yet as severe as those in the south.