Hispidus Populations Research Articles

The effect of disturbance and drought on Hairy Jointgrass (Arthraxon hispidus) in north coast New South Wales: Understanding threatened species populations in a dynamic landscape

AbstractEcological disturbances such as fire, grazing or mechanical cultivation can promote or suppress plant populations within vegetation communities. Therefore, such processes can threaten vulnerable species, or play a significant role in their conservation, so an understanding of a species’ ecological response to disturbance is foundational to threatened species management. Various types of anthropogenic disturbance are listed as threats to the vulnerable‐listed Arthraxon hispidus (Hairy Jointgrass) (Poaceae) in NSW; however, there is evidence that slashing, grazing and fire can stimulate the recruitment and establishment of this annual species in some circumstances. We undertook field experiments to investigate the effects of each of these disturbance regimes on A. hispidus populations over two growing seasons within modified wetlands/moist pastures in north coast NSW. We found that the application of fire in winter had a stronger promotional effect on A. hispidus recruitment than slashing, though both treatments increased its abundance and reduced the height and cover of surrounding vegetation, particularly exotic perennial grasses. Following initial establishment, A. hispidus declined under drought conditions during the study, and continuous grazing exacerbated this effect. Drought also increased the abundance of introduced species relative to native wetland species across the study sites. Results confirm that disturbance, particularly fire, can promote A. hispidus populations in some vegetation communities; however, climatic variation also plays a role in its population dynamics. Consideration of each of these factors and their potential interactions is important when developing conservation approaches for this threatened species.

Waterlogging tolerance of the threatened grass Arthraxon hispidus and implications for its habitat niche within endangered wetlands in north-eastern New South Wales

Knowledge of a target species’ habitat niche and physiological tolerances is important for conservation planning. However, these factors are not well understood for the threatened annual grass Arthraxon hispidus in New South Wales (NSW). Although the species is widespread in modified environments, recent studies have suggested that several threatened wetland types may represent original native habitat for the species, but documented field examples are lacking and the species’ physiological response to soil moisture is not clear. We undertook a detailed survey of an A. hispidus population within a relatively intact native sedgeland community, and carried out a nursery experiment to test the hydrological tolerances of the species. We found that A. hispidus plants grew more vigorously in poorly drained or waterlogged conditions, suggesting that the species is well-adapted to overcome such stressors, possibly through the formation of adventitious roots, a trait shared by many wetland plants globally. Our field survey confirmed that the A. hispidus population within the study site occurred only within species assemblages that were characteristic of a freshwater wetland formation and that matched descriptions of a listed endangered ecological community. These findings provide a deeper insight into the species’ habitat and threats, and offer a valuable management focus for conservation of A. hispidus as a component of threatened wetland communities in north-eastern NSW.

Taxonomy, diet and geographical provenance of fossil species of Sigmodon from west central Mexico during the late Pleistocene

The information of diet, habitat and geographic location of animals obtained from fossil deposits is important to understand the environmental changes of a place that occurred through time. Most of the paleoecological research in Mexico is centered on large mammal taxa. A minimal research effort is allocated to small vertebrates which due to their relative brief longevity and small territories, provide fine-scale paleoenvironmental information. In the present work, the occlusal morphology of the first molar was analyzed, as well as the dental microwear marks and the 87Sr/86Sr isotopic ratio in fossil and extant relatives of the genus Sigmodon from La Cinta-Portalitos locality, situated on the northern portion of the Cuitzeo Basin, central western Mexico. Goals included determining species richness within Sigmodon, as well as dietary behavior and geographic origin. Based on the comparison of the occlusal morphology of fossils and modern teeth, three fossil species were distinguished: S. hispidus, S. leucotis and S. alleni. Microwear patterns showed that S. hispidus population could be associated to a grazer diet, inhabiting open areas, similar to the extant populations. The species S. leucotis exhibited a microwear signature associated to a grazer diet as well, and S. alleni revealed a fruit–grass–insect feeding behavior. Finally, in the case of S. hispidus, the 87Sr/86Sr isotopic signature proved to be like that of the bedrock, so the S. hispidus population was local and a suitable indicator of paleoenvironmental conditions of La Cinta-Portalitos.

Fire can promote germination, recruitment and seed bank accumulation of the threatened annual grass Arthraxon hispidus

Disturbance plays an important role in plant life history strategies and has been documented as both enhancing and threatening populations of the vulnerable grass Arthraxon hispidus (Thunb.) Makino (hairy jointgrass) on the NSW north coast. Mechanical disturbance (slashing) is often used in A. hispidus conservation management, but many Australian plants are adapted to fire-based disturbance regimes. In this study we undertook a field burning experiment, along with soil seed bank sampling and germination trials, to explore how fire influences A. hispidus population dynamics in terms of plant recruitment and seed bank fluctuations. We found that winter burning strongly promoted A. hispidus spring germination without entirely depleting the residual seedbank. Although drought affected our field study population, burning also led to increased adult cover and substantial seed bank replenishment the following autumn. Exposure to a smoke treatment almost doubled the germination rate of A. hispidus seeds in nursery trials. Our study suggests that appropriate burning regimes can help to maintain this species in the landscape, by both structural and chemical mechanisms, by enhancing plant recruitment and facilitating seed bank accumulation. However, some A. hispidus plants also successfully germinated, established, and reproduced in unburnt plots during our study, suggesting that populations of this species can persist without disturbance in some habitats, such as native wetland communities. We found that A. hispidus has a multi-year seed longevity and a persistent seed bank, providing the species a degree of resilience in the event of unpredictable disturbance regimes and climatic anomalies.

The habitat and management of hairy jointgrass (Arthraxon hispidus, Poaceae) on the north coast of New South Wales, Australia

Ecological information about threatened species is required to guide strategic management approaches for effective biodiversity conservation in Australia. Arthraxon hispidus (hairy jointgrass) is a listed threatened species in New South Wales (NSW), but there is limited information on its habitat preferences and native vegetation associations, as well as the impact of historical and ongoing anthropogenic disturbance on its distribution and abundance. In the present study, populations of A. hispidus on the north coast of NSW were surveyed to investigate the habitat characteristics associated with various occurrences of the species. Its preferred habitat was found to be dense ground-cover formations in high-moisture, low-canopy conditions. Cover was highest in moisture-associated assemblages in and around wetlands, drainage lines and groundwater seepages, often in association with native grasses, sedges and herbs. These findings suggest that naturally open freshwater wetland communities comprise the most plausible native habitat niches for A. hispidus populations on the north coast of NSW. A. hispidus also occurs widely among introduced pastures and weeds in previously forested areas, demonstrating the species’ potential to exploit derived habitat. Results indicate that, although ongoing disturbance continues to promote A. hispidus in these exotic-dominated landscapes where historical clearing has created potential habitat opportunities, anthropogenic disturbance (slashing or cattle grazing) is not necessary to sustain A. hispidus within native-dominated wetland communities. Findings suggest more scope for integrated management of A. hispidus within broader native vegetation conservation strategies rather than a single species approach.

The Bionomics of the Cocoa Mealybug, Exallomochlus hispidus (Morrison) (Hemiptera: Pseudococcidae), on Mangosteen Fruit and Three Alternative Hosts.

The cocoa mealybug, Exallomochlus hispidus Morrison (Hemiptera: Pseudococcidae) is known to attack mangosteen, an important fruit export commodity for Indonesia. The mealybug is polyphagous, so alternative host plants can serve as a source of nourishment. This study aimed to record the bionomics of E. hispidus on mangosteen (Garcinia mangostana L.) and three alternative hosts, kabocha squash (Cucurbita maxima L.), soursop (Annona muricata, L.), and guava (Psidium guajava L.). First-instar nymphs of the E. hispidus were reared at room temperature on mangosteen, kabocha, soursop, and guava fruits until they developed into adults and produced nymphs. Female E. hispidus go through three instar stages before adulthood. The species reproduces by deuterotokous parthenogenesis. Exallomochlus hispidus successfully developed and reproduced on all four hosts. The shortest life cycle of the mealybug occurred on kabocha (about 32.4 days) and the longest was on guava (about 38.3 days). The highest fecundity was found on kabocha (about 100 nymphs/female) and the lowest on mangosteen (about 46 nymphs/female). The shortest oviposition period was 10 days on mangosteen and the longest, 10 days, on guava. These findings could be helpful in controlling E. hispidus populations in orchards.

不同坡向荩草构件的权衡关系

权衡关系是植物生活史对策理论的基础，研究不同坡向植物构件的权衡关系对理解植物在不同生境下的表型可塑性具有重要意义。本研究选取济南市长清区琵琶山不同坡向的典型植物--荩草(Arthraxon hispidus)为研究对象，分析了不同坡向影响下荩草种群构件间的关系。结果表明：坡向是影响荩草构件权衡的重要地形因子，从构件形态看，南坡的荩草相比北坡来说更倾向于茎叶生物量的增长，北坡的荩草则表现出以更大的茎节间长；从异速生长关系看，叶宽、叶面积和株高在各坡向不具有共斜率，采取不同的分配策略，其它构件在各坡向具有共斜率，只是在分配方面略有倾向。不同坡向荩草构件的权衡关系反映了异质生境中资源多重竞争下荩草生物量的分配机制和提高种群适应性的种群更新策略。 Trade-off is the basis of plant life history strategy theory. It’s very important to study the trade-off among plant modules in different aspects for understanding the phenotypic plasticity of plants under different habitat conditions. In this study, we selected one common plant-Arthraxon hispidus, on Mount Pipa in Changqing district, Jinan city as the focal species. We studied the relationship between modules of A. Hispidus populations under the effects of different aspects. The results showed that aspect had a significant effect on the trade-off of modules of A. Hispidus populations. Biomass of stems and leaves of plants on south slope was higher than those on the north slope. While, A. hispidus on the north slope improved the internode length adapting to the environment. The allometric relationships of leaf width, leaf area and height vs. plant biomass were different on different slopes, which were affected by different aspects of slopes. While the allometric relationships of other modules vs. plant biomass were not affected by different aspects of slopes. The trade-off between different modules showed that A. Hispidus can choose effective biomass allocation and regeneration strategies to survive the multiple resource competitions in heterogenous habitats.

Fast and slow dynamics of northern small mammal populations

Animal populations interact with their environments in a scale-dependent manner and exhibit scale-dependent dynamics. Animals may adjust reproductive frequency and fecundity in response to fluctuating environments to maximize reproductive success. We hypothesize that populations of insectivorous small mammals undergo seasonal variations owing to predictable shortages of winter food and short breeding periods, whereas populations of herbivorous small mammals may exhibit multi-year fluctuations owing to food-induced variability in the length of the breeding period among years. We predict that omnivorous Peromyscus and Reithrodontomys species would have population dynamics patterns similar to insectivorous small mammals, if the omnivorous rodents rely on insects as winter food. Using the wavelet transform, we re-analyzed nine long-term monthly population time series of Blarina brevicauda, Microtus ochrogaster, Microtus pennsylvanicus, Peromyscus leucopus, Peromyscus maniculatus, Reithrodontomys megalotis, and Sigmodon hispidus from Illinois, Kansas, and Pennsylvania, United States to test our hypothesis. Populations of B. brevicauda in Illinois, P. leucopus in Pennsylvania, and S. hispidus and R. megalotis in Kansas resonated with climate change at an annual scale (8–16 months), whereas Microtus populations in Illinois and Kansas and P. leucopus, P. maniculatus, and S. hispidus populations in Kansas exhibited the greatest variability at a scale of 32 months. Our Kansas M. ochrogaster population cycled every 2–3 years from 1984 to 1994. Therefore, small mammal populations form a continuum of slow–fast dynamics. Variation in small mammal population abundances is related to climate dynamics only at annual scales. However, it is unlikely that long-term dynamics of local climate directly result in long-term variation in small mammal population abundances, including population cycles. Our findings demonstrate the importance of scale-specific effects of exogenous factors in the dynamics of animal populations and offer a new interpretation of complex effects of climate on population dynamics.

Genetic structure among and within populations of the serpentine endemic Heteropappus hispidus ssp. leptocladus (Compositae)

Heteropappus hispidus ssp. leptocladus is an edaphic endemic taxon that is confined to serpentine and limestone-derived soils and is allopatrically distributed in three regions of western Japan. In this study, we attempted to detect genomic signatures of seven H. hispidus ssp. leptocladus populations along with eight other subspecies populations using eight nuclear microsatellite loci. The Mantel test supported an isolation by distance model across all H. hispidus populations, thus implying the possibility of parallel evolution for each subspecies. Results from AMOVA recognized relatively larger differentiations in geographic distribution compared to intraspecific taxonomy. Relationships indicated by neighbor-joining phylogenetic tree analysis and population structure generally did not reflect an intraspecific taxonomy. Populations from limestone-derived soil harbored a homogeneous genetic structure with neighboring populations from serpentine-derived soils. These results suggest that the edaphic ecotype may have derived allopatrically while a lack of edaphic constraint existed between serpentine and limestone soils.

Analysis of Relationship of the Korean Styracaceae by RAPD Markers

In order to estimate the relationships among four taxa (Styrax japonicus, Styrax obassia, sηrax shiraianus and Pterostyrax hispidus) of two genus in the Styracaceae and their regional populations, RAPDs analysis was performed. Fifteen random primers generating 238 RAPD bands were enough to reveal differences in genotype bands. They were clustered into three groups by the UPGMA phenogram. The first group was Styrax japonicus populations, the second group was consisted of Styrax obass따 populations and S. shiraianus populations, and third group was Pterostyrax hispidus population The UPGMA phenogram based on RAPD analyses showed that Styrax obassia and S. shiraianus had the closest relationship among four taxa. Species as well as genera of the Korean Styracaceae were well discriminated by the RAPD analyses.

Black Creek Canal Virus infection in Sigmodon hispidus in southern Florida.

A total of 1,500 small mammals were collected and tested for antibodies cross-reactive to Sin Nombre virus (Hantavirus: Bunyaviridae) at 89 sites in a 1,600 km2 study area of southern Florida. More than 95% of the 123 seropositive animals were cotton rats (Sigmodon hispidus), suggesting infection by Black Creek Canal Virus, although seroreactive Rattus rattus (5 of 294) and Peromyscus gossypinus (1 of 39) also were captured. Crude seroprevalence in S. hispidus was 11%. Seroprevalence increased with body size and was more common in male (18%; n=451) than in female (6%; n=593) cotton rats. Infection within S. hispidus populations was widespread throughout the study area. Prevalence ranged from 0% to 60% at sites where more than five cotton rats were sampled but was not only a function of sample size. Sites with seropositive cotton rats were geographically clustered compared with sites with no seropositive cotton rats. Clustering was not due to the spatial distribution of sites with few animals, season of collection, or sex bias of animals captured at these sites. However, sites with no seropositive animals had an excess of animals in the intermediate size class (60-99 g) and a deficit of the largest and smallest animals. These data suggest that population structure within the habitat mosaic may play a significant role in the spatial distribution of hantavirus infection in local populations of reservoir species.

Effects of Supplemental Food on Population Dynamics of Cotton Rats, Sigmodon Hispidus

Variation in resource abundance affects population dynamics by altering demographic processes and interactions among individuals in the population. For small mammals, food is likely to be a critical resource. Population densities should vary directly with food abundance, but the underlying demographic changes are more difficult to predict. We experimentally increased food available to populations of hispid cotton rats, Sigmodon hispidus, to examine how rates of recruitment and disappearance varied with food abundance. We expected supplemental food to increase winter survival and to increase recruitment, perhaps advancing the date of first reproduction in the spring. We also thought larger, behaviorally dominant animals might dominate the point sources of supplemental food, altering age or size ratios and producing an excess of transient animals. Supplemental food increased population densities but did not dampen pronounced seasonal fluctuations. Supplemented populations contained proportionately more juveniles and small adults than did controls; social behavior may have limited increases in numbers of large adults. Survival rates did not change; density increases were due to increased reproduction and immigration. In supplemented populations, reproductive effort by females increased, but the proportion of reproductive females decreased. Reproductive females and nonreproductive animals of both sexes were less likely to be transients than were reproductive males. Transients constituted higher proportions of control populations because of successful settlement, primarily by juveniles and small adults, into supplemented areas. The strongly seasonal climatic conditions under which northern S. hispidus populations exist produce contrasting selective pressures which might favor season—specific foraging strategies. Our data support a scenario of territorial females and wandering males in the reproductive season, with females maximizing resource acquisition for production of offspring. During winter, both sexes may restrict foraging time (and exposure to predators and weather) to the minimum required for survival.

Temporal Variation in Humoral and Cell‐Mediated Immune Response in a Sigmodon Hispidus Population

We examined the hypothesis that environmentally induced alteration of immunocompetence is a primary physiological mechanism by which population survival is regulated. The involvement of disease and immunocompetence in the regulation of small mammal populations is not well understood but a strong relationship between physiological stress and immunity has been demonstrated. Its involvement is further supported by several studies, which have provided evidence that survival, incidence of disease, and selected gross measures of immunity change temporally with density and season. We examined this hypothesis by documenting the existence of temporal alterations in selected measures of both humoral and cell—mediated immune function in a population of cotton rats (Sigmodon hispidus), a species known to fluctuate widely in density, inhabiting a tallgrass prairie in central Oklahoma. A total of 310 cotton rats was collected from August 1989 to May 1991 (10 collections) using conventional live—trap methods. In addition to morphological characteristics of primary and secondary lymphoid organs, the ability of splenocytes to produce specific antibody in response to a single injection of sheep erythrocytes and to proliferate in response to in vitro exposure to mitogens was measured to assess immunocompetence. Whole blood was collected for the determination of total peripheral blood leukocyte counts, packed cell volume, and total serum proteins. Statistically significant differences in all variable except total serum protein existed among the 10 collections and most of this variability was independent of specific seasonal time periods. Bimodal thythmicity was characteristic of temporal changes for several measures of immunocompetence. Changes over time in the average immunocompetence of this population could have reflected a shift in genotypic polymorphism; several other plausible explanations are offered to explain the observed temporal patterns.

Interactions Between the Cotton Rats, Sigmodon fulviventer and S. hispidus

Interactions between two sympatric species of cotton rat, Sigmodon fulviventer and S. hispidus, were studied for 1 year. Both species had similar ecological requirements and occurred in bunchgrass (Sporobolus wrightii) on the central plateau in Durango, Mexico. Demographic changes in S. hispidus populations following experimental removal of S. fulviventer, the numerically dominant animal, included: (1) higher population levels; (2) slightly higher survival rates; (3) slightly greater life expectancy; (4) occupation of areas formerly held by S. fulviventer; and (5) greater distances captured from individual centers of activity. These changes were attributed to S. hispidus immigrating into an unoccupied space in habitat common to both species and less opportunity for interspecific interactions following removal of S. fulviventer. A postexperimental trapping study 1 year later revealed that S. fulviventer had increased its populations to near preremoval levels and had reinvaded and reoccupied areas held by S. hispidus during the removal experiment. Correspondingly, the S. hispidus population had decreased and been displaced by S. fulviventer. It was concluded that both species were interacting in unmanipulated populations, but that the interactions were of a passive (avoidance) nature. These interspecific interactions may influence population regulation, habitat selection, geographical range-extending ability and evolution in both species. Although competitive interactions were not demonstrated, certain data suggested the possibility of some form of interspecific competition. At present, S. fulviventer appears to be the numerically and interactively dominant Sigmodon. INTRODUCTION Intersp-ecific interactions between closely related small mammals arem difficult to demonstrate and evaluate in field situations. Baker (1969) observed that when two species of grass-eating, runway-making rodents of the genus Sigmodon (cotton rats) live in the same area, one is generally abundant and the other less abundant. Such a situation existed in the desert-grassland ecotone of E-Central Durango, Mexico (240 38' N lat and 1030 42' W long). S. fulviventer Allen, usually abundant, and S. hispidus Say and Ord, usually uncommon, were resident in bunchgrass (Sporobolus wrightii) habitat. Hence, this area offered an excellent opportunity to study population dynamics and interactions of both species. Adults of S. fulviventer and S. hispidus in this part of Mexico have similar body weights and measurements but are easily distinguished by different hair colors and other characteristics (Baker, 1969). This study attempts to describe the numerical and spatial relationships between these cotton rats, and to demonstrate certain demographic changes which occur when sympatric populations of these 1 Present address: Department of Zoology and Entomology, Iowa State University, Ames 50010.

The Effects of Northward Dispersal on Growth Rate of Young, Size of Young at Birth, and Litter Size in Sigmodon hispidus

Northward dispersal in Sigmodon hispidus has not significantly affected early growth rate of young or size of young at birth. But there has been a significant increase in litter size in the northern population. Northern S. hispidus have the same size young, but more young per litter than the southern population. Maintenance of the size of young at birth in northern populations may be related, in part, to the development of thermoregulatory capabilities. In the northern population there was seasonal variation in litter size, growth rate (tail length), and size of young at birth (tail length and body weight). Litters of S. hispidus produced in cold weather months are significantly smaller than those produced in warm weather months. INTRODUCTION The northward dispersal of the hispid cotton rat (Sigmodon hispidus spp.) has been well documented over most of its geographical range (Patton, 1941; Rinker, 1942; Cockrum, 1948; Anderson and Berg, 1959; Jones, 1960, 1964; Mohlhenrich, 1961; Genoways and Schlitter, 1966). With increasing latitude, populations of S. hispidus encounter increased seasonal climatic variability and longer cold periods. Populations of S. hispidus show both seasonal and irregular long-term fluctuations in density. Irregular fluctuations in population, frequently to plague proportions, have been reported in both southern and northern populations (for a review of the literature see Goertz, 1964). Odum (1955) demonstrated three well-marked long-term cycles in a southern population of S. hispidus hispidus, although in all years the autumn density of cotton rats was markedly greater than the spring density. He considered the latter type of variation a northern-type seasonal cycle in these populations. Northern-type in density have also been observed in other southern populations of S. hispidus (Erickson, 1949; Dunaway and Kaye, 1964). In northern populations of S. hispidus, seasonal in population are better defined and more regular as a result of decreased temperature (and increased duration of low temperatures) associated with increased latitude (Goertz, 1964; unpublished data). Variation in S. hispidus populations appears to be regulated by temperature (Baumgartner, 1945; Sealander and Walker, 1955; Dunaway and Kaye, 1964; Goertz, 1964). Goertz (1964) found that a long period of below-freezing weather, snow cover, and frozen ground coincided with a population decline. Similar declines had four factors in common: (1) high summer and autumn population density; (2)