Invasive plant species are a growing concern in many regions of the world, yet little information is available on the effects of habitat type and distance to urban settlements on the ability of alien ...plants to become established. We studied plant communities from the arid steppes to the Andean forest within two national parks and surroundings, in northwestern Patagonia, Argentina. Alien and native vascular plant species were sampled using 90 × 100 m
2 plots and analyzed in relation to both climatic and environmental variables and distance to urban centres. We also compared life-forms of alien and native species. Precipitation and distance to an urban centre were important determinants of alien species community richness and composition, and shrubland sites had significantly more alien species than forest or steppe sites. Alien flora (15% of the species) was composed of a higher proportion of annuals and biennials than native flora. Our results suggest that precipitation, distance to source population, and anthropogenic disturbance influence the invasion process in this region, together with the availability of open niches. This work stresses the importance of monitoring invasive species in natural reserves, and of considering habitat types as well as idiosyncratic characteristics of the non-natives for developing management strategies.
► Shrublands within heterogeneous temperate regions are rich in plant species and especially prone to alien plants invasions. ► Urban settlements in these areas and the availability of open niches also influence the invasion process in this region. ► Management strategies for protected areas should consider habitat types and the characteristics of the invaders.
Early competition between native and non-native species can greatly influence ecosystem integrity through its effect on species regeneration, which can be further modulated by environmental context.
...Bromus tectorum
(cheatgrass
,
winter annual grass) has recently invaded the temperate grasslands of Patagonia Argentina ecosystems mainly used for extensive livestock raising. We evaluated the relative impact of competition from
B. tectorum
on two native species with different life-forms, from the seedling stage:
Vulpia australis
, the only winter annual grass in the community, and
Bromus setifolius
, a perennial grass highly palatable to livestock. The effect of asymmetric competition between
B. tectorum
(seedling or adult individuals) on
B. setifolius
was also assessed. A greenhouse experiment was conducted to simulate interspecific competition (two species per pot), and control (one species per pot) treatments. We regulated the recruitment timing of all studied species to represent realistic competition dynamics in the field.
Bromus tectorum
had a greater negative impact on the growth of both native species relative to the effect produced by a co-occurring native, even when that native was ecologically equivalent to the invader. Also, the impact of
B. tectorum
on
B. setifolius
depended on the invader’s developmental stage, with bigger individuals having the largest impact. In contrast, native species hardly affected
B. tectorum
development. Our findings indicate that native grasses may not hinder the spread of
B. tectorum
through competition. Moreover,
B. tectorum
could have a negative impact at the community level through its effect on the recruitment of native species, probably exacerbating degradation in overgrazed areas.
Summary
Bromus tectorum (cheatgrass) is an aggressive invasive species posing threats to native ecosystems including increase in fire frequency, alteration of water and nutrient cycles and exclusion ...of native species. As such, it is important to monitor this species worldwide. However, outside the United States, it has been poorly studied. We studied this species at two scales: (i) at a local scale, evaluating the species presence and its determinants, along the ecotonal area between the steppe and the forest within north‐western Patagonia, to reveal whether B. tectorum is actually invading natural ecosystems in areas comparable with those invaded in USA, and (ii) at a regional scale, through a search of literature and herbaria databases on B. tectorum in South America, to determine the current known distribution of the species in this subcontinent. Results indicate that it is already invading north‐western Patagonia in Argentina, mainly in the semi‐arid part of the region, and that precipitation influences the invasion process. We found that for South America, B. tectorum has been only documented in southern Argentina and Chile. Given the similarities to other invaded regions, the possibility of invasion for Patagonia has been predicted but not prevented. It is important to study changes in the invasion level where it is already established, and to encourage managers with prevention and control strategies. Combining this information with lessons from places with extensive periods of invasion could help to initiate management of the species in areas where the invasion process is beginning and before the species spreads widely.
Soil nitrogen mineralisation (N
), the conversion of organic into inorganic N, is important for productivity and nutrient cycling. The balance between mineralisation and immobilisation (net N
) ...varies with soil properties and climate. However, because most global-scale assessments of net N
are laboratory-based, its regulation under field-conditions and implications for real-world soil functioning remain uncertain. Here, we explore the drivers of realised (field) and potential (laboratory) soil net N
across 30 grasslands worldwide. We find that realised N
is largely explained by temperature of the wettest quarter, microbial biomass, clay content and bulk density. Potential N
only weakly correlates with realised N
, but contributes to explain realised net N
when combined with soil and climatic variables. We provide novel insights of global realised soil net N
and show that potential soil net N
data available in the literature could be parameterised with soil and climate data to better predict realised N
.
Outcrops around the world enhance biodiversity as they provide heterogeneous environments and varied habitats for species with different requirements than those living in the surroundings, and in ...this way they increase alpha and beta diversity. We studied the floristic composition of the vegetation of rock outcrops in northwestern Patagonia, Argentina, and compared them to the surrounding matrix of shrubland and steppe. For this we sampled 50 outcrops and 50 matrix plots close to them, identified all the species present, and analyzed their floristic composition with Detrended Correspondence Analysis (DCA). We also analyzed the floras of the north and south faces of the outcrops. The resulting ordinations were related to geographic gradients of the region. The proportions of alien to native species, different life forms, and phylogenetic groups of the outcrop floras were compared to the matrix with G-tests. Our results showed similar dominant families, life form proportions and percentage of alien species in the outcrops and the surrounding matrix. However, species composition of the outcrops was markedly different. North Patagonian outcrops present several taxa not found in the matrix, especially in their southern, less insolated walls. The previously recorded distribution of most of these exclusive species is found in colder areas further south. Thus, we hypothesize that outcrops could be acting as relicts of cold-adapted glacial paleofloras that were probably more extended during glacial times and retreated south after the last glacial maximum.
Human disturbance can be a severe problem for some animal species. Behavioural ecology theory predicts that sensitivity to mortality risks, and thereby to disturbance, will be related to life-history ...characteristics. Long-lived species with low reproductive rates are expected to have a high cost of predation and therefore avoid risks strongly. In this paper we quantify the effect of roads on the Andean condor (
Vultur gryphus) using behavioural indicators. We used a pair wise design, offering condors standardized food patches near and far from roads simultaneously. The patches consisted of dead adult sheep. We recorded condors’ behaviour when visiting each patch. This study establishes the versatility of behavioural indicators and their usefulness to study conservation problems. We found that, although near and far patches were discovered after similar times and there were similar numbers of condors in the vicinity of near and far patches, the use of patches differed strongly. In the patches far from roads many more condors came to feed, the average time spent per individual was longer, the proportion of time spent vigilant was lower, and the amount of food left uneaten on the carcasses was lower. These results strongly suggest that Andean condors clearly avoid roads, and behave in a way predicted from theory if they trade off safety for energy. This study shows that roads have stronger influence on the habitat use of Andean condors, than previously thought, and may be a significant problem for the species in populated areas.
Summary
Bromus tectorum
(cheatgrass) is an aggressive invasive species posing threats to native ecosystems including increase in fire frequency, alteration of water and nutrient cycles and exclusion ...of native species. As such, it is important to monitor this species worldwide. However, outside the United States, it has been poorly studied. We studied this species at two scales: (i) at a local scale, evaluating the species presence and its determinants, along the ecotonal area between the steppe and the forest within north‐western Patagonia, to reveal whether
B. tectorum
is actually invading natural ecosystems in areas comparable with those invaded in USA, and (ii) at a regional scale, through a search of literature and herbaria databases on
B. tectorum
in South America, to determine the current known distribution of the species in this subcontinent. Results indicate that it is already invading north‐western Patagonia in Argentina, mainly in the semi‐arid part of the region, and that precipitation influences the invasion process. We found that for South America,
B. tectorum
has been only documented in southern Argentina and Chile. Given the similarities to other invaded regions, the possibility of invasion for Patagonia has been predicted but not prevented. It is important to study changes in the invasion level where it is already established, and to encourage managers with prevention and control strategies. Combining this information with lessons from places with extensive periods of invasion could help to initiate management of the species in areas where the invasion process is beginning and before the species spreads widely.
Cubic CaSiO3 perovskite is a major phase in subducted oceanic crust, where it forms at a depth of about 550 kilometres from majoritic garnet1,2,28. However, its rheological properties at temperatures ...and pressures typical ofthe lower mantle are poorly known. Here we measured the plastic strength of cubic CaSiO3 perovskite at pressure and temperature conditions typical for a subducting slab up to a depth of about 1,200 kilometres. In contrast to tetragonal CaSiO3, previously investigated at room temperature3,4, we find that cubic CaSiO3 perovskite is a comparably weak phase at the temperatures of the lower mantle. We find that its strength and viscosity are substantially lower than that of bridgmanite and ferropericlase, possibly making cubic CaSiO3 perovskite the weakest lower-mantle phase. Our findings suggest that cubic CaSiO3 perovskite governs the dynamics of subducting slabs. Weak CaSiO3 perovskite further provides a mechanism to separate subducted oceanic crust from the underlying mantle. Depending on the depth of the separation, basaltic crust could accumulate at the boundary between the upper and lower mantle, where cubic CaSiO3 perovskite may contribute to the seismically observed regions of low shear-wave velocities in the uppermost lower mantle5,6, or sink to the core-mantle boundary and explain the seismic anomalies associated with large low-shear-velocity provinces beneath Africa and the Pacific7-9.
Abstract
Global patterns of regional (gamma) plant diversity are relatively well known, but whether these patterns hold for local communities, and the dependence on spatial grain, remain ...controversial. Using data on 170,272 georeferenced local plant assemblages, we created global maps of alpha diversity (local species richness) for vascular plants at three different spatial grains, for forests and non-forests. We show that alpha diversity is consistently high across grains in some regions (for example, Andean-Amazonian foothills), but regional ‘scaling anomalies’ (deviations from the positive correlation) exist elsewhere, particularly in Eurasian temperate forests with disproportionally higher fine-grained richness and many African tropical forests with disproportionally higher coarse-grained richness. The influence of different climatic, topographic and biogeographical variables on alpha diversity also varies across grains. Our multi-grain maps return a nuanced understanding of vascular plant biodiversity patterns that complements classic maps of biodiversity hotspots and will improve predictions of global change effects on biodiversity.
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