Semiarid Thorn Scrub Research Articles

Positive relationship between seedlings and saplings with adult trees at small scale influenced by dispersal vectors in semiarid thornscrub

Positive relationship between seedlings and saplings with adult trees at small scale influenced by dispersal vectors in semiarid thornscrub

Exclusion of small mammals and lagomorphs invasion interact with human-trampling to drive changes in topsoil microbial community structure and function in semiarid Chile

Species losses and additions can disrupt the relationship between resident species and the structure and functioning of ecosystems. Persistent human-trampling, on the other hand, can have similar effects through the disruption of biocrusts on surface soils of semiarid systems, affecting soil stability and fixation of carbon and nitrogen. Here, we tested the interactive and synergistic impacts of the exclusion of native mammalian herbivores and the effects of introduced lagomorphs in a semiarid thorn scrub ecosystem, where soils were subjected to two different trampling intensities (i.e., trampled and non-trampled). We postulated that because of their differential habitat use and fossorial activities, with respect to native small mammals, lagomorphs would have strong negative effects on soil structure, biocrust cover, and biocrust bacterial community structure. Our expectations were that changes in biocrust cover in response to trampling where native mammals were excluded, but exotic lagomorphs were present, will spread their impacts on soil chemical and physical features. To test our hypotheses, we measured changes in soil biogeochemical properties in four experimental plots where lagomorphs (L)/small mammals (SM) were experimentally manipulated to exclude them from the plots (−), or let them be present (+). The experimental combinations monitored were: -L/+SM, -L/-SM, +L/+SM, and +L/-SM. Results showed that human-trampling disturbance interacted with the loss of native small mammals and the presence of non-native lagomorphs to cause large changes on biological (i.e., biocrust cover, bacterial and nifH genes abundance), physical (i.e., soil moisture and soil stability) and chemical (i.e., TC and TN) soil features. The relative impacts of trampling disturbance on biological and physicochemical features were strongly influenced by the presence of non-native lagomorphs. For example, larger decreases in biocrust cover and bacterial abundance were observed in treatments without lagomorphs (-L/+SM; -L/-SM). In turn, losses of biocrust cover, in addition to trampling, determined decreases in soil stability in all treatments. These results suggest that non-native lagomorphs surpass the effects of the loss of native small mammals in reducing soil quality and productivity. Therefore, human-trampling has the potential to convert low disturbed soils, as those observed in non-trampled soils in treatments -L/+SM, -L/-SM into poor soils with low biocrusts cover and concomitant low stability, as observed in +L/+SM; +L/-SM treatments. These findings agree with previous observations that different components of global change act in synergic ways in fragile, water-limited environments. Because biological invasions and soil surface disturbance are becoming widespread in dryland regions globally, understanding the long-term consequences of these interactions is essential.

Use of shelter tubes, grass‐specific herbicide, and herbivore exclosures to reduce stressors and improve restoration of semiarid thornscrub forests

AbstractIn semiarid south Texas, land conversion has reduced thornscrub forests by greater than 95%, and stressors, including competition with invasive grasses, mammalian herbivory, and drought, threaten the success of restoration efforts. This study assessed the effectiveness of multiple restoration treatments aimed at improving survival and growth of thornscrub forest seedlings planted in old agricultural fields. In January 2013, we treated greater than 1,100 seedlings with grass‐specific herbicide, herbivore exclosures, and shelter tubes, used separately or combined. We further evaluated the effects of shelter tube duration (0, 6, 12, and 18 months). For each seedling, we quantified surrounding invasive grass cover, browse intensity, height, and basal diameter every 4 months until September 2014. Herbicide application decreased invasive grass cover approximately 5‐fold and increased seedling survival (23%) and basal diameter (26%). Shelter tube application for 12 and 18 months increased seedling survival (10%) and height (43 and 74%, respectively), whereas seedlings treated with tubes for only 6 months performed similar to those left untreated. Exclosures had no impact on seedling survival but increased seedling height (23%) and basal diameter (26%). We found no significant interactive effects of treatments. Overall, herbicide most effectively increased seedling survival and basal diameter growth, whereas shelter tubes proved most useful for promoting height growth. Combined, these treatments increased implementation and maintenance costs 2‐fold, but minimized seedling mortality and maximized restoration potential. These findings highlight the necessity of post‐planting seedling management to reduce stress from invasive grasses, mammalian herbivory, and drought and improve restoration potential in semiarid thornscrub forests.

Rainfall, microhabitat, and small mammals influence the abundance and distribution of soil microorganisms in a Chilean semi-arid shrubland

Patterns in rainfall and soil water availability are considered to be the main drivers governing arid and semiarid ecosystems. While the mechanisms by which water limits aboveground net primary production has been widely explored, few long-term studies have examined interactions between precipitation, soil resources, plant communities, and soil microbial communities; these may be critical to understanding soil biogeochemical cycles and above- and belowground interactions. We capitalized on a long-term biotic manipulation (exclusion of small mammal herbivores from replicate plots) and long-term variation in rainfall to assess how precipitation, small mammals, and shrub cover act directly and interactively to influence the spatial and temporal distribution of soil microorganisms, a key first step to understanding soil biogeochemical cycles. We measured the abundance of arbuscular mycorrhiza (AM), soil fungi, soil bacteria, and soil physicochemical characteristics over 10 consecutive years in a semiarid thorn scrub community in north–central Chile; we sampled two microhabitats (under shrub cover, and in open spaces between shrubs colonized by ephemeral plants), and in plots with or without the presence of native small mammals, the main herbivores in this environment. Annual rainfall ranged widely (11–356 mm) in this period and was the primary factor affecting abundance of AM root colonization and soil microbes. While the percentage of root length with AM was higher in dry compared to wet years, free-living soil bacteria and fungi were more abundant during wet years. All microorganisms were more abundant in the resource islands beneath the shrubs compared to open microhabitat between shrubs, although the relation between soil biota and the concentration of some particular nutrients was negative. These patterns were modulated by the presence of small mammals, which enhanced root colonization by AM fungi, particularly for ephemeral plants, but which were negatively associated with soil fungi abundance. The abundance of soil bacteria showed a more complex response to the presence of small mammals and was dependent on microhabitat and year. The spatial and temporal heterogeneity of soil resources and the activity of small mammals are important modulators of subterranean biotic responses to rainfall, the primary factor affecting soil microbiota abundance in this semiarid ecosystem.

Patterns in arthropod abundance and biomass in the semiarid thorn scrub of Bosque Fray Jorge National Park, north-central Chile: A preliminary assessment

In 2003, we initiated a sampling protocol for arthropods as part of long-term field experiment in a semiarid thorn scrub community in north-central Chile. We utilized pitfall and Malaise traps to sample terrestrial and volant arthropods, respectively. Inventories were conducted for 4 days and nights monthly. We posited that arthropod abundance and biomass would track environmental changes such as high rainfall often due to El Niño Southern Oscillations (ENSOs). Peaks in both abundance and biomass for terrestrial and volant arthropods were in similar months (spring–early summer; August–November); arthropods also tracked high rainfall years in 2004, 2006, and 2011, due mostly to increases in a few dominant groups, i.e., tenebrionid beetles (Coleoptera) in terrestrial sampling, and moths (Lepidoptera: Noctuidae, microlepidoptera) in aerial sampling. However, the same groups increased dramatically in 2008 which was a below-average rainfall year. Numerical decreases in late summer-fall months (January–April) were more abrupt for terrestrial arthropods than for volant ones. Both terrestrial and volant arthropods reached their lowest levels in winter months (June–July). Some evidence suggests long-term shifts in the composition of volant taxa. Arthropods likely are important prey items for insectivorous reptiles (i.e., lizards), birds, and an insectivorous small mammal, the elegant mouse opossum (Thylamys elegans), and future efforts are being directed towards examining the evidence for correlated changes in those consumers with arthropod abundance and biomass.

Biotic interactions and community dynamics in the semiarid thorn scrub of Bosque Fray Jorge National Park, north-central Chile: A paradigm revisited

In 1989, we initiated a long-term field experiment in a semiarid thorn scrub community in north-central Chile. We posited that biotic interactions, particularly predation, interspecific competition, and herbivory assumed a primary top-down role in affecting small mammals and annual plants here. Using a multi-factorial design we selectively excluded vertebrate predators (principally carnivores and raptors) and a large small mammal herbivore, the degu (Octodon degus), from replicated 0.56 ha exclosures located in a valley near the coast in Bosque Fray Jorge National Park. Evidence initially supported effects of predator exclusion on O. degus but not for other small mammals in the assemblage (e.g., Phyllotis darwini, Abrothrix olivaceus). Subsequent years of monitoring have documented that predation has temporary effects on degu numbers, but that populations of this and other small mammals are much more strongly influenced by environmental bottom-up factors (i.e., rainfall). Further, our experimental manipulation has provided no evidence for negative interspecific competition effects on numbers of any small mammal in this assemblage. Degu exclusions, however, have had negative indirect effects on exotic annuals; native annuals appear to outcompete exotics especially during drought years The effect is magnified in all-small mammal exclusions. Since about 2002, selective exclusions of lagomorphs and small mammals have resulted in changes in cover of some perennial shrubs. Also notable has been a fundamental shift in the small mammal composition following the last major El Niño Southern Oscillation (ENSO) event in 2000–2002; degus now comprise a majority of small mammal biomass in the assemblage, and their numbers have become more stable and less temporally variable. This appears to have been caused by a shift in rainfall periodicity from strong interannual fluctuations in response to periodic ENSOs, to a more equitable pattern with more consistent annual rainfall. This represents one of the first documented cases of system-wide biotic phase shifts to a relatively modest change in rainfall regime. This may be indicative of ongoing climate change in the Chilean semiarid region, and we expect that further changes in the community will occur if those trends continue.

Growth and survival of thornscrub forest seedlings in response to restoration strategies aimed at alleviating abiotic and biotic stressors

Semi-arid thornscrub forests occur throughout South Texas and northeastern Mexico and provide habitat for numerous fauna, including the Federally-endangered ocelot. However, <2% of original thornscrub remains due to land conversion for human use. One attempt underway to restore thornscrub habitat around core ocelot populations in South Texas is the planting of thornscrub seedlings in old agricultural fields. However, growth and survival post-planting and effectiveness of restoration strategies to overcome common stressors (e.g., competition, herbivory, and drought) have not been evaluated. In March 2011, we initiated a pilot study to assess seedling growth and survival in response to pre-planting prescribed fire, mowing, herbicide, and shelter tubes aimed at alleviating stressors including invasive grass cover and herbivore browse. We found that a single pre-planting prescribed fire promoted invasive grass cover; mowing had no effect. Glyphosate reduced invasive grass cover, but acetic acid/orange oil was ineffective. Seedlings in fire plots were tallest with the largest basal diameters despite greater invasive grass cover. Shelter tubes promoted height growth, reduced browse, and increased survival. This research will help managers decide which restoration techniques most effectively reduce thornscrub seedling stressors and promote growth and survival.

Dietary supplementation in domestic goats may reduce grazing pressure on vegetation in semi-arid thornscrub

Small herds of domestic goats play an important role in the subsistence of farmers in semi-arid subtropical areas. Dietary supplementation of these animals may help these farmers to improve productivity, but an assessment of compatibility with the sustainable development of these areas is necessary prior to the implementation of such a management strategy. In this study, we examined the effects of diet supplementation on domestic goat foraging behavior during the dry season, by analyzing the forage diet composition of supplemented and unsupplemented goats over a period of four months (February–May). Diet composition was analyzed using direct observation of each animal and recording time spent on consumption of each different plant species. Initial and final live weights of all the animals were taken. Supplementation allowed animals to maintain higher bodyweight with low modification of dietary selection and no increase in consumption of endemic or sensitive plant species. Supplementation could also help to reduce the detrimental consequences of free foraging during the dry season, by decreasing the time spent foraging, which would indirectly benefit the conservation of natural vegetation during this critical period.

Seed dispersal by domestic goats in a semiarid thornscrub of Mexico

Previous studies conducted in the semiarid thornscrub of the Biosphere Reserve of Tehuacán-Cuicatlán have reported a high consumption of cactus and legume fruits by domestic goats. To test the hypothesis that goats may effectively disperse seed, we collected domestic goat feces from different microhabitats (bare ground, under shrub or under tree). The area occupied by each microhabitat was measured in the field. We then quantified the presence of viable seeds in goat feces and their deposition in microhabitats suitable for seedling establishment. We collected 209 seeds and using a seed reference collection, we identified these as belonging to three endemic cactus species, two legumes and several unidentified species. A high proportion of the cactus seeds germinated. Although most of the feces were found in open areas, more than 30% were recorded beneath the canopies of perennial plants, a suitable microhabitat for seedling establishment and survival. Contrary to the general assumption that goats cause only degradation of vegetation, these findings show that goats can effectively disperse viable seeds of diverse species. Studies that evaluate the ecological role of goats as important elements of biotic interactions are needed in order to generate an adequate management program for livestock.

Seed Removal Rates Under Isolated Trees and Continuous Vegetation in Semiarid Thornscrub

Abstract Clearing native vegetation to increase the amount of land available for agriculture in northeastern Mexico has left remnants ranging in size from fragments of continuous vegetation to isolated individual trees. These provide valuable opportunities for restoring larger areas of native vegetation. We explored whether fragmentation of Tamaulipan thornscrub affects the removal of seeds from 12 woody species that encompass a range of sizes and dispersal mechanisms. We tested whether (1) seed removal rates under isolated trees were higher than under continuous vegetation; (2) dispersal structures, such as fleshy pericarps, made some seeds more attractive to seed removers; and (3) microenvironmental variation affected seed removal rates. Seeds were placed under canopies of Texas ebony (Ebenopsis ebano) and Mesquite trees (Prosopis laevigata). Seed removal trials were conducted three times, each trial lasting 30 days. Most seeds were removed in all trials by the end of one month. Seed removal rate was slower under isolated trees. In general, fleshy fruits were removed faster than other fruits; whole fruits and fleshy tissue were removed faster than depulped seeds. In species with fleshy pericarps, acid washing of seeds, to simulate seeds processed in the digestive tract of dispersers, reduced the seed removal rates, suggesting that it would be a good pre‐treatment for restoration efforts.

Frugivory and seed dispersal by foxes in relation to mammalian prey abundance in a semiarid thornscrub

Abstract We examine the role of the native fox, Pseudalopex culpaeus, as a frugivore and seed disperser in a semiarid thornscrub of Chile. We quantified the fruit and animal components in its diet versus the availability of fruits and small mammals in the field over a 2‐year period (January 1998 through February 2000). We tested the legitimacy and effectiveness of foxes as dispersers by quantifying the percentages of seed viability and of germination of seeds that passed through fox gut versus those picked from plants. We also studied their efficiency as dispersers, monitoring the fate of seeds in faeces placed in the field. The highest frequencies of fruit consumption by foxes were observed when abundances of small mammal prey were &lt;6 individuals per hectare, regardless of fruit abundance in the field. Thus, foxes consumed fruits as a supplementary food resource. Based on 326 faeces, the total number of fruits consumed was about 34 000 over the 2‐year study period, and fruits from the alien shrub Schinus molle represented 98% of that total, with the native Porlieria chilensis a distant second. Germination and viability of defecated seeds of P. chilensis were reduced by 66% and 48%, respectively, in comparison to controls. In contrast, germination of seeds of S. molle increased by 50% and no effect on viability was observed. With regard to P. chilensis, foxes were legitimate (they defecated viable seeds), but ineffective (seeds in faeces had lower germination than those taken directly from parental plants and there was no seedling establishment in the field) and inefficient dispersers (seeds in faeces were deposited on microhabitats hostile to seed germination and seedling establishment). However, with regard to S. molle, foxes were legitimate, effective (seeds in faeces had higher germination than those taken directly from parental plants; there was germination but no establishment in the field), and efficient dispersers (over 41% of seeds were deposited on safe microsites). Thus, a native fox may be contributing to the spread of an alien shrub, co‐opting existing community processes.

Thirteen Years of Shifting Top-Down and Bottom-Up Control

For 13 years, we studied the role of biotic interactions, including predation, herbivory, and interspecific competition, in a semiarid thorn scrub community in north-central Chile. Using a large-scale field manipulation, we monitored changes in small mammals, plants, and vertebrate predators. We documented important “top-down” predation effects on some small-mammal species, and small-mammal effects on some plant species resulting from experimental exclusions. However, periodic El Niño Southern Oscillation (ENSO) events caused several high rainfall episodes during this interval, resulting in large “bottom-up” increases in both plants and animals. Therefore, we suggest that instead of exclusive top-down or bottom-up control, this system undergoes shifting control, with relatively greater importance of biotic interactions in wet years and of resource limitation in dry ones. Because intervals between ENSO events are long and responses are slow, long-term studies are essential for understanding such effects in semiarid or arid systems.

Results of a food addition experiment in a north‐central Chile small mammal assemblage: evidence for the role of “bottom‐up” factors

Since 1989, effects of biotic interactions including predation and herbivory have been examined in a replicated experimental study in a north‐central Chilean semiarid thorn scrub community. Strong responses of small mammals and plants to El Niño Southern Oscillations (ENSO) have also been documented suggesting that “bottom‐up” factors related to high rainfall are important. To simulate increased primary productivity effects on small mammals, ad lib rabbit pellet additions were initiated in mid‐1997 on unfenced grids near the experimental complex. Following the 1997 El Niño event with three times normal precipitation, numbers of small mammals during pre‐addition months and the first treatment year were similar on control and food addition grids. During the second year (1998–1999), a period of severe drought, food additions had significant positive effects on numbers of two predominantly herbivorous “core” (resident) species, Octodon degus and Phyllotis darwini, and an omnivorous “quasi‐core” (resident but highly fluctuating) species, Akodon olivaceus; however, all three species declined towards the end of the second treatment year. Two “opportunistic” (temporarily resident) species, Abrothrix longipilis (an insectivore) and Oligoryzomys longicaudatus (a granivore), showed no responses to food additions. An insectivorous marsupial, Thylamys elegans (also a “core species”), had significantly lower numbers on food addition grids. Changes in body weight distributions and proportions of reproductive individuals particularly in O. degus indicate in situ responses. Whereas no differences in residency, numbers of stations visited, and trappability were observed, energy compensation ratios greater than one suggest significant immigration in the second year. Thus, food additions elicited strong responses by herbivorous/omnivorous “core” and “quasi‐core species” whereas they had no effects on “opportunistic species”. These results reinforce the view that “bottom‐up” factors influencing food availability exert prevailing control on numerically important small mammal species by temporarily increasing carrying capacity, and that “top‐down” factors (i.e., biotic interactions) become important when small mammal numbers are at or near their carrying capacity. Spatial dynamics may be important in explaining declines of species populations exhibiting initially positive responses to food additions.

The Competitiveness of Natural Fibers Based Composites in the Automotive Sector: The Sisal Agribusiness in Brazil

The Northeast Region of Brazil has a land area of over I.5 million km2 and extends over tropical and equatorial latitudes from 18' S in the State of Bahia to 1' S in the State of Maranhão. Although representing only about 18% of the national territory, it is the home of approximately 35% of Brazil's 160 millions inhabitants (IBGE, 2000). The Northeastern region of Brazil, in the States of Bahia, Paraiba and Rio Grande do Norte are responsible for 100% of sisal production. Precipitation is the key environmental factor of ecological significance for the region and can be characterized by three major zones trending east to west. First is a narrow humid coastal strip in the cast (known as Zone of Mata) which receives an average of 1,250 mm to over 2,000 mm of rainfall per annum. Behind this humid zone there is a middle one with moisture deficiency (subject to periodic droughts) which accounts for the largest portion of the Northeast. Most of this zone receives less than 1,000 mm of annual rainfall, with an extreme low of less than 300 mm in some areas. The third zone is one of high rainfall, over 2,000 mm per year, in western Maranhão. Reflecting this wide diversity of moisture conditions are natural vegetation patterns ranging from tropical rainforest (“Atlantic Rain Forest”) to semi-arid thorn scrub (“Caatinga”). This system has been under severe pressure due to the lack of economical alternatives to support the population living in those areas.

The Interplay of Biotic and Abiotic Factors in a Semiarid Chilean Mammal Assemblage: Results of a Long-Term Experiment

Since early 1989, we have conducted a large-scale ecological manipulation in a semiarid thorn scrub community in north-central Chile. We have excluded vertebrate predators (raptors and mammalian carnivores), and larger small mammal herbivores/ competitors (i.e., degus, Octodon degus) from replicated 0.56-ha plots, and monitored small mammal population and plant responses over more than ten years. Repeated tneasures ANOVAs on minimum number known alive (MNKA) estimates of small mammals for a six-year period (1990-1996) spanning an El Nino event in 1991-1992 showed strong responses of some species to predator exclusions (e.g., O. degus; Darwin's leaf-eared mouse, Phyllotis darwini; the chinchilla-rat, Abrocoma bennetti). However, responses varied in time with significant effects during pre-El Nino (1990-1992) and El Nino (1992-1994) periods (i.e., O. degus), or pre-El Nino and post-El Nino (1994-1996) periods (P. darwini, A. bennetti). Other species showed no responses to predator exclusions (e.g., olivaceous field mouse, Akodon olivaceus; long-haired field mouse, Abrothrix longipilis; long-tailed rice rat. Oligoryzomys longi-caudatus). Some effects of competitor (degu) exclusions were detected (e.g., A. bennetti during the El Nino and post-El Nino periods; O. longicaudatus during the El Nino). Top-down' factors (i.e., biotic interactions) appear to have greater effects on core species (i.e., P. darwini, O. degus) which persist in the thorn scrub. Other species (e.g., A. longipilis, O. longicaudatus) are transitory residents or opportunistic with lesser effects of biotic interactions, and their populations may be controlled by source-sink dynamics. All species had strong responses to the 1991-1992 El Nino indicating primary control by bottom-up factors.

Effects of vertebrate predation on a caviomorph rodent, the degu (Octodon degus), in a semiarid thorn scrub community in Chile.

The effects of vertebrate predation have been monitored since 1989 on 16 replicated 0.56 ha study plots in a semiarid thorn scrub community in north-central Chile. Using fences of different heights with and without holes and suspended game netting to alter principal predator (foxes and raptors) and large rodent herbivore (Octodon degus) access, four grids each have been assigned to the following treatments: 1) low fencing and holes allowing free access of predators and small mammals; 2) low fencing without holes to exclude degus only; 3) high fencing and netting with holes to exclude predators only; and 4) high fencing and netting without holes to exclude predators and degus. Small mammal population censuses are conducted monthly using mark-recapture techniques. Degu population trends during 1989 and 1990 showed strongly but nonsignificantly lower numbers in control plots during months when densities were characteristically low (September-November) for this seasonally reproductive species; since March 1991, differences have become persistent and increasingly significant. Predators appear to have greater numerical effects when their prey populations are low. Survival times of degus, particularly established adults, were significantly longer in predator exclusion grids during the 2 1/2 years of observation; thus, predation also affects prey population structure.

Floristic and structural variation in the Tamaulipan thornscrub, northeastern Mexico

Abstract. A generalized research strategy is presented for identifying the ecological effects of the physical environment and management in a poorly known region of subtropical, semiarid thornscrub in northeastern Mexico. Vegetation samples were stratified across a small number of climatic subregions, substrate types and topographic situations. Classification analysis and PCo A of the species x site matrix of incidence data after application of the Information Statistic were used. The analyses suggested that the regional variation in climate, substrates and topography was responsible for the major floristic differences in the vegetation. The distributions of most plant species were related to the variation in the physical environment. PCo A of the species x site cover data after application of the Bray‐Curtis dissimilarity metric revealed evidence of vegetation change due to overgrazing in each major floristic group, but not to selective cutting for timber and firewood.

More Thoughts on Vertebrate Predator Regulation of Prey

Previous articleNext article No AccessNotes and CommentsMore Thoughts on Vertebrate Predator Regulation of PreySam Erlinge, Gorgen Goransson, Goran Hogstedt, Goran Jansson, Olof Liberg, Jon Loman, Ingvar N. Nilsson, Torbjorn von Schantz, and Magnus SylvenSam Erlinge Search for more articles by this author , Gorgen Goransson Search for more articles by this author , Goran Hogstedt Search for more articles by this author , Goran Jansson Search for more articles by this author , Olof Liberg Search for more articles by this author , Jon Loman Search for more articles by this author , Ingvar N. Nilsson Search for more articles by this author , Torbjorn von Schantz Search for more articles by this author , and Magnus Sylven Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 132, Number 1Jul., 1988 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/284842 Views: 3Total views on this site Citations: 21Citations are reported from Crossref Copyright 1988 The University of ChicagoPDF download Crossref reports the following articles citing this article:Anders Pape Møller, Timothy A. 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Resource Patitioning in a Chilean Semi-Arid Small Mammal Community

SUMMARY (1) Patterns of habitat and food utilization among small mammals were studied for 17 months in a Chilean semi-arid thorn scrub community. This community is dominated by spiny drought-deciduous and evergreen shrubs and low but variable winter rainfall. The four major small mammal species included three cricetid and one octodontid rodent, and three additional species (two rodents and one marsupial) which were low to sporadic in occurrence. (2) The four major small mammal species demonstrated significant patterns of habitat association including affinity for sites with high shrub cover and/or low to moderate grass and forb cover (three cricetid species), and affinity for sites with low grass and forb cover and high bare ground cover (the octodontid species). (3) Habitat overlap between these species as determined by similarity in utilization of trap and tracking stations over 3-month periods was high especially in comparison to values of overlap revealed in studies of California small mammal communities. (4) Trophic specializations among the seven small mammal species indicated three foraging guilds with two species each (herbivore, insectivore and granivore) and one omnivorous species were present in the community. Dietary overlap between the four major species was similar to that observed in more diverse California small mammal communities. (5) Niche overlap was relatively high for this community due primarily to high habitat overlap. Contrary to patterns revealed in California small mammal communities, but similar to other Chilean small mammal communities in the mediterranean zone, habitat overlap was usually greater than dietary overlap. (6) Levels of certain food resources including herbaceous plants, insects and seeds are at least equal and possibly greater in Chile than in California. This pattern in conjunction with the presence of similar dietary overlaps in both areas may indicate lower levels of competition among Chilean small mammals for those resources. (7) The patterns of resource utilization demonstrated by this community seem to be due more to ecological factors than to the evolutionary and biogeographical characteristics of the Chilean small mammal fauna.

Trophic Relationships among Small Mammals in a Chilean Semiarid Thorn Scrub Community

The food habits of seven species of small mammals were analyzed for a 15-month period during a live-trapping and snap-trapping study in a semiarid thorn scrub community in north-central Chile. The species included four cricetids (Akodon olivaceas, A. longipilis, Phyllotis darwini, and Oryzomys longicaudatus), two caviomorphs (Octodon degus and Abrocoma bennetti), and a didelphid (Marmosa elegans). The community was characterized by a semiarid mediterranean climate with low winter precipitation and frequent fog formation. Dominant physical features included high cover of spiny evergreen and drought-deciduous shrubs, low ground cover of herbaceous plants, and open sandy areas. Year-round food habit trends indicated three functional trophic guilds and one omnivorous species. A. longipilis and M. elegans were insectivorous, O. degus and A. bennetti were herbivorous, P. darwini and O. longicaudatus were granivorous, and A. olivaceus was omnivorous. This pattern of trophic specialization agrees generally with other studies of various species in the Chilean region, and suggests contrasts with patterns in the mediterranean and desert communities of North America and Argentina.