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Suitable Microsites (suitable + microsite)
Selected AbstractsIntegrating physiology, population dynamics and climate to make multi-scale predictions for the spread of an invasive insect: the Argentine ant at Haleakala National Park, HawaiiECOGRAPHY, Issue 1 2010Stephen Hartley Mechanistic models for predicting species' distribution patterns present particular advantages and challenges relative to models developed from statistical correlations between distribution and climate. They can be especially useful for predicting the range of invasive species whose distribution has not yet reached equilibrium. Here, we illustrate how a physiological model of development for the invasive Argentine ant can be connected to differences in micro-site suitability, population dynamics and climatic gradients; processes operating at quite different spatial scales. Our study is located in the subalpine shrubland of Haleakala National Park, Hawaii, where the spread of Argentine ants Linepithema humile has been documented for the past twenty-five years. We report four main results. First, at a microsite level, the accumulation of degree-days recorded in potential ant nest sites under bare ground or rocks was significantly greater than under a groundcover of grassy vegetation. Second, annual degree-days measured where population boundaries have not expanded (456,521,degree-days), were just above the developmental requirements identified from earlier laboratory studies (445,degree-days above 15.9°C). Third, rates of population expansion showed a strong linear relationship with annual degree-days. Finally, an empirical relationship between soil degree-days and climate variables mapped at a broader scale predicts the potential for future range expansion of Argentine ants at Haleakala, particularly to the west of the lower colony and the east of the upper colony. Variation in the availability of suitable microsites, driven by changes in vegetation cover and ultimately climate, provide a hierarchical understanding of the distribution of Argentine ants close to their cold-wet limit of climatic tolerances. We conclude that the integration of physiology, population dynamics and climate mapping holds much promise for making more robust predictions about the potential spread of invasive species. [source] Seed predation, not seed dispersal, explains the landscape-level abundance of an early-successional plantJOURNAL OF ECOLOGY, Issue 4 2006JOHN L. ORROCK Summary 1Plants may not occur in a given area if there are no suitable sites for seeds to establish (microsite limitation), if seeds fail to arrive in suitable microsites (dispersal limitation) or if seeds in suitable microsites are destroyed by predators (predator limitation). 2We conducted a large-scale study to determine the importance of dispersal limitation and predator limitation in affecting the distribution of pokeweed, Phytolacca americana, in 401-ha experimental patches arrayed in eight groups of five patches distributed across a 300-km2 region. 3Microsite limitation was minimized by clearcutting and burning existing vegetation, creating the type of disturbed habitat in which P. americana readily germinates and establishes. The role of dispersal limitation was examined by adding approximately 7000 seeds to each of eight patches in March 2000. The role of seed predation was examined in all 40 patches using experimental exclosures from June 2000 to July 2001. 4The number of P. americana plants in September 2000 was unchanged by seed addition. However, fewer P. americana plants were found in patches where seed predators removed more P. americana seeds from experimental exclosures. These data suggest that P. americana is not limited by seed dispersal. Rather, in habitats where microsites are readily available, the abundance of P. americana among patches appears to be limited by the activities of seed predators. 5When dispersal and microsites are not limiting, the role of local seed predators can be important for generating emergent, large-scale patterns of plant abundance across landscapes. Moreover, because predators may generate large-scale patterns that resemble other forms of limitation and predators may target specific species, predator impacts should be more frequently incorporated into experiments on the role of seed limitation and plant community composition. [source] Sex-related spatial patterns of Poa ligularis in relation to shrub patch occurrence in northern PatagoniaJOURNAL OF VEGETATION SCIENCE, Issue 1 2000Mónica B. Bertiller Correa (1969,1988) Abstract. Poa ligularis is a dioecious species and a valuable forage plant which is widespread in the arid steppe of northern Patagonia (Argentina). The vegetation in these areas consists of a system of perennial plant patches alternating with bare soil areas defining contrasting micro-environments. We hypothesized that (1) male and female individuals of P. ligularis are spatially segregated in different micro-environments, (2) the intensity of spatial segregation of sexes depends on plant structure and (3) spatial segregation of sexes is enhanced by competitive interactions between the sexes within the vegetation patches. We analysed the spatial distribution of female and male individuals in relation to the spatial pattern of vegetation in two areas differing in their vegetation structure. The location of P. ligularis within patches where either male, female or both sexes occurred was also analysed. The results indicate that different patterns of spatial distribution of sexes of P. ligularis may be found at the community level depending on the dominant life forms and geometric structure of plant patches. Where patches are of a lower height, with a high internal patch cover, individuals of both sexes are concentrated within patch canopies. In sites characterized by large, tall patches and less internal patch cover suitable microsites for female and male P. ligularis occur both within and outside the patch with males located at further distances from the patch edge. Where the patch is large and tall enough to allow the establishment of males and females at relatively high numbers, males occupy the patch periphery or even colonize the interpatch bare soil. These spatial patterns are consistent with selective traits in which females better tolerate intraspecific competition than males, while males tolerate wider fluctuations in the physical environment (soil moisture, nitrogen availability, wind intensity, etc.). [source] Factors Affecting the Distribution and Abundance of Asplenium nidus L. in a Tropical Lowland Rain Forest in Peninsular MalaysiaBIOTROPICA, Issue 4 2010Liwen Zhang ABSTRACT Asplenium nidus is an abundant epiphytic fern of tropical rain forests in the Old World, where it plays an important ecological role in the forest canopy as host to diverse arthropod communities. We investigated the factors that determine the distribution and abundance of A. nidus in the canopy of an aseasonal lowland dipterocarp forest at Pasoh Forest Reserve, Malaysia. We found that A. nidus was more abundant in the understory, and on hosts with smooth bark and relatively flat branch angles. Ferns were found on a wide diversity and size range of host taxa. However, both host taxa and host diameter at breast height had a significant effect on A. nidus occupancy. Asplenium nidus had an aggregated spatial distribution at all scales within the study area. Spatial aggregation at larger scales appears to be driven by habitat preference, as A. nidus abundance was positively associated with swampy areas and negatively associated with hilly areas. At smaller scales, limited dispersal of their wind-dispersed spores most likely explains the aggregated distribution. Larger individuals occurred higher in the canopy and were more common in the hilly area. Thus, the distribution of A. nidus may represent a trade-off between the availability of suitable microsites for establishment in the understory and better growth conditions higher in the canopy. However, A. nidus is known to comprise a complex of cryptic species, and future studies should incorporate molecular techniques to elucidate the potential role of speciation in explaining these patterns. Abstract in Malaysian is available at http://www.blackwell-synergy.com/loi/btp [source] | ||||||||||