Higher Percent Cover Research Articles

The Relative Importance of Seeding Method, Soil Ripping, and Soil Variables on Seeding Success

AbstractWe conducted a field experiment to examine how seeding method, soil ripping, and soil characteristics affected the initial establishment and growth of seeded species and if differences among treatments persisted into the second growing season. We planted seeds into a compacted field plot where most of the topsoil had been removed. The native seed mixture of Artemisia californica, Eschscholzia californica, Eriogonum fasciculatum, Lupinus succulentus, Nassella pulchra, and Vulpia microstachys represented different seed sizes and life histories. Three seeding methods (hydroseeding, imprinting, and drilling) and three ripping depths (0, 20, and 40 cm) were combined in a factorial experiment. Soil organic matter and NO3− were used as covariates. For two years, we measured density, percent cover, mean size, and flower production of the selected species, and weed emergence. Only seeding method and soil variation affected initial establishment of natives. Small‐seeded species had higher density in imprinted and hydroseeded than drilled treatments, whereas large‐seeded species had higher density in imprinted and drilled than hydroseeded treatments. These patterns persisted with only slight modification into the second year. Weed density in year 1 decreased with soil ripping. In year 1, Vulpia height and Lupinus height and flowering were greater with drilling or imprinting than hydroseeding but were not affected by ripping. Eschscholzia, Lupinus, and Vulpia produced seeds in the first year, but only Vulpia reestablished successfully in the second year. Vulpia had high cover in the second year that increased with increasing NO3−, but did not vary by treatment. In year 2 perennial Nassella, and to some extent Eriogonum, grew largest, produced more inflorescences, and had their highest percent cover in the 40‐cm rip treatment. Size and inflorescence production also increased with increasing NO3−; sometimes this relationship was stronger than the effects of treatments. We found only positive associations between estimated biomass (density × height) of annuals and survival of shrubs. Potential for erosion control, as measured by total density in year 1 and total vegetative cover in year 2, was greatest in imprinted and hydroseeded treatments and increased with increasing NO3−. This relatively simple experiment yielded information critical to understanding optimum seeding methods and seedbed preparation and indicates that seeding method can be determined by seed size and germination biology. Although an experiment such as this enables some generalizations, it does not eliminate the need for site‐specific experiments prior to restoration.

Rapid assessment of macro algal cover on intertidal sediments in a nutrified estuary.

Macroalgal blooms have been considered to be an indicator of eutrophication. A new and rapid method is described for the assessment of macroalgal cover in the intertidal zone of estuaries. Macroalgal cover in the intertidal of the nutrient-enriched River Deben estuary was found to reach a maximum of 50% coverage, but this varied seasonally with the highest percentage cover during June and July. Macro-algae mats were particularly associated with areas of hard substrata providing suitable attachment points, rather than with the nutrient concentrations along the estuary. The occurrence of macroalgae may be more related to the substrate than to the nutrient status of the estuary.

Seasonal dynamics and recruitment strategies of the invasive seaweed Grateloupia doryphora (Halymeniaceae, Rhodophyta) in Narragansett Bay and Rhode Island Sound, Rhode Island, USA

Although there is considerable interest in the introduction and spread of invasive species, there has been little research documenting growth patterns of a specific organism from the time of its first arrival. This paper addresses the seasonality and recruitment of Grateloupia doryphora, a large red algal species that arrived in Narragansett Bay, Rhode Island, USA, in 1994. From 1997 to 1999 inclusive, this species exhibited a distinct seasonal pattern, with the lowest percent cover occurring in May–June and the highest percent cover in October. This timing of low and high percent cover was observed concurrently at three stations over a two-year period. Percent cover was a function of blade size and numbers. New blades appeared year-round. In addition to percent cover, blade colour changed seasonally from light red (June–August) to dark burgundy (August–January) to yellow red (February–May). Strategies for recruitment of G. doryphora were observed in the field, on both natural and artificial substrata (fixed plastic plates coated with sand), and in culture. Recruitment on sand-coated plates in Narragansett Bay and Rhode Island Sound resulted from spore settlement and subsequent crust and blade development. On a single plate, hundreds of juvenile upright blades appeared in May–June 1999, and the largest blades grew to 25 cm long by August. In addition to recruitment on plates, crusts appeared on bare rock, and new blades arose from crusts and from proliferations of older blades. Laboratory cultures clarified the developmental sequence from spore to crust to blade and/or upright filaments to new crusts and new blades. The crustose form may provide a strategy for survival during unfavourable environmental conditions, enabling G. doryphora to establish residency in Rhode Island waters. The effect of this invasive species on other organisms has yet to be determined.

Microhabitat and plant structure of Compsopogon coeruleus (Compsopogonaceae, Rhodophyta) populations in streams from São Paulo State, southeastern Brazil

Microhabitat distribution was investigated in three populations of C. coeruleus to determine the distributional patterns and their controlling factors, as well as morphometric adaptations to varying conditions on a scale of a few centimetres. Morphometric variations and their relations with physical variables (current velocity, irradiance, depth and type of substratum) revealed some particular characteristics for each population and indicate particular adaptations. However, some trends were clear: 1) larger plants (length and/or diameter) produced a higher quantity of monosporangia in the three populations; 2) plant length and diameter were positively correlated in two populations; 3) plant diameter was positively correlated with current velocity in two populations; 4) higher percent cover was associated with substrata composed of macrophytes in two populations. C. coeruleus occurred under relatively wide microhabitat conditions and had high niche width values, suggesting a tolerance to considerable variation in physical variables. These characteristics contribute to the species' wide distribution in Brazilian streams, both spatial (at distinct scales) and seasonal.

Effects of landscape spatial structure on movement patterns of the hispid cotton rat (Sigmodon hispidus)

A large-scale experimental landscape study was conducted to examine the use of corridors and the forest matrix habitat by the hispid cotton rat (Sigmodon hispidus). The role of micro- habitat selection by S. hispidus in influencing routes of movement was also investigated. The experimental landscape consisted of ten 1.64-ha patches (each 128×128 m) established in a loblolly (Pinus teada) forest. Four of the patches were isolated while the other six were connected in pairs by a 32-m wide corridor. Cotton rats (N=96) were simultaneously released into both an isolated and connected patch, and monitored by radiotelemetry for 10 days. We found that the forest matrix was not a barrier to movements of cotton rats. Fifty percent of the cotton rats moved through the matrix. Corridors had no significant effect on the number of animals leaving connected patches (60%) compared to isolated patches (50%). However, corridors were the preferred route to leave a connected patch. Colonization success for cotton rats leaving connected and isolated patches did not significantly differ. Cotton rats exhibited micro-habitat preferences and these preferences differed within patch/corridor and matrix habitats. In patch/corridor habitats, cotton rats selected sites with tall (>1 m) shrubs and high percent cover. In the forest matrix, cotton rats selected sites with abundant cover by vines and low tree canopy cover. Movement patterns of Sigmodon hispidus are not strongly influenced by large-scale landscape spatial structures. Micro-habitat selection, however, does influence movement patterns. These findings have important implications regarding habitat connectivity for small mammals.

Periphyton community structure and dynamics in a subarctic lake

Periphyton species composition was analysed at 20 stations around an island in a large (1239 km2) oligotrophic lake in subarctic Quebec (Lac à l'Eau Claire; latitude 56°10′N, longitude 74°30′W) to describe the mature communities colonizing the upper littoral region and to evaluate periphyton abundance and distribution relative to the physical environment. Four major communities could be clearly distinguished in the field by their macroscopic features, specifically colour (black, brown, and green) and growth form (filamentous or encrusted), as well as by their standing stock (cover and areal Chl a concentration) and photosynthetic characteristics. (1) Black crust—This community was dominated by the cyanobacterium Gloeocapsa, with highest percent cover in shallow waters (≤ 0.25 m) protected from wave action by offshore boulder barriers. Photosynthesis under full sunlight was low per unit biomass (0.7 μg C∙(μg Chl a)−1∙h−1). (2) Brown film—This community was dominated by Calothrix, with Gloeocapsa and Phormidium as subdominants. Maximum abundance was at 0.5 m, with photosynthetic rates that were similar to the black community. (3) Green crust—This community was dominated by the mucilaginous chlorophyte Gloeocystis, with Oscillatoria as subdominant, and colonized shallow depths (≤ 0.25 m) in the shaded underlayer of rocks. It had slow, light-limited photosynthetic rates (0.1 μg C∙(μg Chl a)−1∙h−1). (4) Green filaments—This community was dominated by Ulothrix zonata, with associated chlorophytes and diatoms, and was a rapidly growing assemblage characterized by the highest diversity, species richness, and productivity per unit biomass (3.5 μg C∙(μg Chl a)−1∙h−1). It occurred on gravel beds at depths < 0.5 m and was restricted to the well-illuminated south-facing shores of the island. Communities 1, 2, and 3 had similar maximum standing stocks throughout the period of sampling (mean of 1.3 μg Chl a∙cm−2), whereas the Ulothrix community rose from 1.9 μg Chl a∙cm−2 in late July to 5.5 μg Chl a∙cm−2 by mid-August. The overall rich biodiversity of the Lac à l'Eau Claire periphyton (> 200 taxa recorded) may reflect the diversity of microenvironments and intermediate disturbance in the upper littoral zone. Key words: cyanobacteria, chlorophytes, diatoms, epilithon, periphyton, photosynthesis.

Response of generalist and specialist insect herbivores to landscape spatial structure

The purpose of this study was to investigate the effect of changes in landscape pattern on generalist and specialist insects. We did this by comparing the species richness and abundance of generalist and specialist herbivorous insects in alfalfa (Medicago sativa, L.) fields on 26 agricultural landscapes that differed in spatial structure. The insects were from the families Curculionidae (Coleoptera), weevils, and Cicadellidae (Auchennorhyncha), leafhoppers. We hypothesized that: (1) generalist richness and abundance would be highest in landscapes with high diversity (Shannon-Wiener); (2) specialist richness and abundance would be highest in landscapes with (i) high percent cover alfalfa and (ii) low mean inter-patch distance. We tested for these effects after con- trolling for the patch-level effects of field size, field age, frequency of disturbance and vegetation texture. The important findings of the study are: (1) generalist richness and abundance increased with increas- ing landscape diversity and (2) isolation (percent cover alfalfa in the landscape and/or mean inter-patch distance) does not affect specialist insects. These results are significant because they indicate that both generalist and specialist insects may move over much larger distances than previously thought. This is one of the first studies to demonstrate a large scale effect of spatial structure on insects across a broad range of landscapes.

<p><strong>Wissenschaftliche Ergebnisse der BRYOTROP-Expedition nach Zaire und Rwanda 6. Lebensformen und Adaptionen zur Wasserleitung und Wasserspeicherung in epiphytischen Moosgesellschaften im östlichen Kongobecken und den angrenzenden Gebirgsstöcken (Parc National de Kahuzi-Biega/Zaire, Forêt de Nyungwe/ Rwanda)</strong></p>

Life forms, water conducting and water storing structures of epiphytic bryophytes are studied along an altitudinal gradient from the eastern Congo basin (tropical lowand zone) to the mountains of the East-African graben (tropical subalpine/alpine zone; BRYOTROP III-transect). Based on a phytosociological analysis, these adaptations were put in relation to the distribution pattern of the bryophyte communities, as well as to the ecological gradient. The interpretation is based on the mean percent cover of each group. The tropical lowland zone is dominated by the life form mat, which is distinctly correlated with watersacs and taxa of the Jubulaceae, Lejeuneaceae and Radulaceae. In the following perhumid montane zone a clear alteration concerning the life form and the adaptations can be observed. The physiognomy of the primary rain-forests now is dominated by fan-forming Plagiochila species which are standing off the phorophyte by its flattened shoots. They are able to condensate water vapour from the fogs as well as using the low light intensities. Within the epiphytes of the bamboo zone of the upper montane zone, similar adaptation strategies to those of the lowland zone can be observed. The communities of the anthropogeneous montane woodlands of this zone, which are rich in mosses, show an ecomorphological wide spectrum [weft and tall-turfs correlated with a central strand (hadrome), hyalocysts and rhizoids]. Within the tropical subalpine/alpine zone exposed to great diurnal variations of climate, mat, weft and cushion-forming tall-turfs dominate, indicating the more xeric conditions (drought stress) by 88 water storing structures (alar cells, central strand, hyalocysts, rhizoids). In this zone, also structures reach a high mean percent cover, which enables the condensation of water vapour from the fog and mist rising from the upper montane zone or which show a groove-like arrangement of the leaflets. This may be recognized as a mechanism enabling a permanent water supply as well as a drain off of surplus water.

Releasing Rain Forest Succession: A Case Study in the Dicranopteris linearis Fernlands of Sri Lanka

AbstractThroughout tropical moist climates, Dicranopteris linearis fernlands can develop as a result of rain forest clearance followed by frequent burning. In Sri Lanka, D. linearis fern‐lands are capable of suppressing the regeneration of rain forest. Field experiments were conducted at Sinharaja Man and Biosphere Reserve, a rain forest where fernlands occupy substantial areas of the reserve boundary. The experiment's objective was to identify methods for initiating forest regeneration in fernlands dominated by D. linearis Three disturbance treatments were used to initiate seedling regeneration: clean weed, root removal, and till. We hypothesized that increasing the severity of the soil disturbance would establish vegetation with higher species richness and diversity, greater above‐ground dry biomass, and higher percentage cover and seedling density. Results indicate only partial support for this hypothesis. Dry biomass was greatest in till treatments, the most severe soil disturbance. By comparison, species richness and diversity, seedling density, and percentage cover were greatest in root‐removal treatments, though in many instances the differences were not significant. The study clearly demonstrated that any kind of soil disturbance can facilitate the establishment of herbs, shrubs, and trees in a fernland dominated by D. linearis. Results showed that herbs, sedges, grasses, and pioneer shrubs represented greater proportions of seedling recruits than did pioneer trees. Seedlings of primary‐forest tree species were nearly nonexistent. In general, results showed that soil disturbance can play an important role in site preparation for the purpose of initiating non‐fern vegetation in fernlands dominated by D. linearis.

Flood and cyclone related loss, and partial recovery, of more than 1000 km 2 of seagrass in Hervey Bay, Queensland, Australia

Approximately 1000 km 2 of seagrass was lost from Hervey Bay after two major floods and a cyclone within a 3 week period in 1992. This represents 24% of the known area of seagrass along the Queensland east coast, which spans 17 degrees of latitude. Anecdotal evidence suggests that such a loss is unprecedented in the past 100 years. The seagrasses in deep water (at least 10 m depth) apparently died as a result of light deprivation caused by a persistent plume of turbid water that resulted from the floods and the resuspension of sediments caused by the cyclonic seas. Seagrasses in shallow water (less than 10 m depth) were uprooted by the heavy seas. Ten months after these events, virtually no recovery was detected. Nearly 2 years after the floods there was substantial recovery, apparently from seed germination, in deep water areas. There was virtually no recovery in shallow water areas (less than 10 m). Sediment disturbance associated with the cyclone may have deeply buried the seeds in shallow areas, or they may have died after being abraded by the churning sediment. The recovering sites in deep water were dominated by Halophila decipiens Ostenfeld, although a few sites had returned to their pre-disturbance state of a high percentage cover of tall Halophila spinulosa (R. Brown) Ascherson with a sparse understorey of Halophila ovalis (R. Brown) Hooker f. Poor catchment management and intensive penaeid shrimp trawling may have exacerbated the effects of the floods and cyclone.

Abundance and distribution of sessile invertebrates under intertidal boulders (São Paulo, Brazil)

The encrusting communities under two boulder fields (Praia Grande and Ponta do Baleeiro) were monitored monthly during 1990 and 1991, in São Sebastião, on the northern coast of São Paulo State, Brazil. Two sizes of boulders were chosen: small (20-30 cm² underside area) and larger ones (160-220 cm²) located on the middle and lower levels of the intertidal. The community's components were mainly sessile animals either compound ones such as Bryozoa, Ascidiacea, Porifera and Cnidaria, in this order of abundance, or simple ones such as Polychaeta and Bivalvia, also in this order of abundance. All groups, except by serpulids (Polychaeta), had higher percent cover in the low intertidal region and under large boulders. Diversity was higher at Ponta do Baleeiro, and in the low intertidal region and on large boulders for both shores.

Abundance and distribution of sessile invertebrates under intertidal boulders (São Paulo, Brazil)

The encrusting communities under two boulder fields (Praia Grande and Ponta do Baleeiro) were monitored monthly during 1990 and 1991, in Sao Sebastiao, on the northern coast of Sao Paulo State, Brazil. Two sizes of boulders were chosen: small (20-30 cm² underside area) and larger ones (160-220 cm²) located on the middle and lower levels of the intertidal. The community's components were mainly sessile animals either compound ones such as Bryozoa, Ascidiacea, Porifera and Cnidaria, in this order of abundance, or simple ones such as Polychaeta and Bivalvia, also in this order of abundance. All groups, except by serpulids (Polychaeta), had higher percent cover in the low intertidal region and under large boulders. Diversity was higher at Ponta do Baleeiro, and in the low intertidal region and on large boulders for both shores.

Marine reserve site selection along the Abel Tasman National Park coast, New Zealand: Consideration of subtidal rocky communities

AbstractAt present, marine reserves do not represent the full range of community types throughout New Zealand.To assist with the placement of a marine reserve along the Abel Tasman National Park coast (northern South Island), dominant subtidal laminarian and fucoid algae, echinoids and herbivorous molluscs were quantitatively investigated. Results from 100 quadrats collected from 19 random transects at six selected sites showed that algae and grazer assemblages varied between granite and limestone substrata.Granite had a high percentage cover of crustose coralline algae (mean 82%–90%), a sublittoral fringe of brown macroalgae and no Ecklonia radiata or red foliose algae. Limestone sites were distinguished by a relatively low percentage cover of coralline algae (mean 13%) and high cover of foliose red algae and E. radiata (2%–36% cover and 0.2–13.9 stipes m−2, respectively).On limestone, molluscs Turbo smaragdus and Cookia sulcata, and the echinoid Evechinus chloroticus were larger than those on granite. On limestone sites with little macroalgae, herbivore size was intermediate. Grazers were more abundant on granite than limestone (mean 34.6 m−2, and 10.8 m−2 respectively).Differences in herbivore composition were recorded between granite substrata, while both algal and herbivore composition varied between limestone sites.We suggest that a variety of environmental factors including substratum influence algal and herbivore assemblages along the Abel Tasman coast.It is recommended that selection of a marine reserve site or sites along the coast of Abel Tasman National Park recognizes differences in community structure both between and within limestone and granite substrata.

The influence of chemistry and habitat features on the microcrustacea of some upland Welsh streams

SUMMARY. 1. Microcrustaceans were sampled during September 1990 from three microhabitats (margins, stony riffles and gravel) at thirteen stream sites in mid‐Wales.2. Patterns in the distribution, abundance and community structure of microcrustacean taxa were related to stream chemistry, physiography, substratum composition and marginal habitat structure. Patterns of distribution between microhabitats were also assessed.3. Chemical variables were the strongest correlates with microcrustacean parameters. Total numbers of microcrustaceans and harpacticoid copepods were reduced at sites with high aluminium concentrations, and ostracods were scarce or absent at the most acidic sites. In contrast, cyclopoid copepods were more abundant and species rich at low pH.4. Microcrustacean communities were most species rich at sites with a high percentage cover of macrophytes on the substratum. Cladoceran species richness and abundance, and the abundance of several microcrustacean species, were also positively correlated with percentage macrophyte cover.5. Three site groupings produced by TWINSPAN classification were primarily related to percentage macrophyte cover and marginal habitat structure, with chemistry and land use also of importance.6. Total microcrustacean abundance was highest in margins, but of all the species, only the harpacticoid Bryocamptus cuspidatus showed a strong microhabitat preference.

Copper rockfish (Sebastes caurinus) and quillback rockfish (Sebastes maliger) habitat in the Strait of Georgia, British Columbia

Densities of copper rockfish (Sebastes caurinus) and quillback rockfish (Sebastes maliger) differ significantly among sites in the northern Strait of Georgia. To determine whether among-site density differences are associated with habitat characteristics of the sites, rockfish densities and habitat characteristics were measured at 12 sites during SCUBA surveys in 1984 and 1985. Quillback rockfish densities were greater in areas of high relief, broken rock, and high percentage cover of flat-bladed kelp, especially on deep transects. Copper rockfish densities were also greater in high relief areas, but effects of other habitat characteristics were not significant. Copper rockfish appeared to be more widely distributed than quillback rockfish over the range of habitats and depths surveyed.

Microhabitat Separation among Sympatric Microtines, Clethrionomys californicus, Microtus oregoni and M. richardsoni

This study examined microhabitat distribution of Microtus oregoni, M. richardsoni and Clethrionomys californicus, sympatric microtine rodents that are similar in morphology and life history patterns. Populations were sampled in riparian and upland habitats within old-growth and mature forest stands in the western Cascade Range of Oregon. As indicated by discriminant function analysis, relative to availability C. californicus occurred in microhabitats with a high percent cover of western hemlock and lichen, low percent cover of deciduous trees and high total length of decayed logs. Microtus oregoni occurred in microhabitats high in percent cover of deciduous herbs, evergreen herbs and deciduous shrubs. Microhabitats where M. richardsoni occurred had a high percent of exposed soil, high total length of recently fallen logs and low percent cover of douglas fir. The results of combining the three microtine species in one discriminant procedure indicated that microhabitat separation among the species was significant and was a function of canopy cover of deciduous trees, percent cover of lichen and distance from streamside.

A quantitative analysis of habitat preferences of Woodcock Scolopax rusticola in the breeding season

In Britain, prior to breeding, Woodcock Scolopax rusticola switch from feeding on pastures by night to feeding in woodland by day. Their major food is earthworms (Lumbricidae). In April and May 1985, vegetation structure and composition and soil parameters including earthworm numbers (30 habitat variables) were recorded for quadrats containing 50 feeding locations of six radio‐tagged birds, seven nests and 50 random locations in Whitwell Wood, northeast Derbyshire.Significantly different mean values between feeding and random sites were found for 11 habitat variables. Feeding sites were in younger stands, with a higher percentage ground cover of dog's mercury Mercurialisperennis and consistently high values for pH. Earthworm biomass was on average 82% greater than in random plots. Areas of beech Fagus sylvaticus were avoided. A discriminant function based on six habitat variables correctly classified 85‐5% of the feeding and random sites; 70% of the feeding locations were correctly classified by a jack‐knife procedure. The important factors determining where feeding occurs are probably safety from avian predators and high availability of earthworms.Discriminant analysis of the habitats used for feeding by solitary birds, broods and for nesting produced significant functions which correctly classified 84% of sites. Nests were in areas with a high percentage cover of brambles Rubus spp. and more open ground vegetation. Broods and solitary birds used similar areas characterized by denser ground vegetation than nest sites.The results of this study indicate that both habitat structure and food availability influence the distribution of Woodcock in the breeding season.

The Effect of Trap Placement on Trapping Success of Rattus-Lutreolus-Velutinus (Thomas) (Muridae, Rodentia) in Northeast Tasmania

The effect of trap placement on the trapping success of Rattus lutreolus velutinus (Thomas) was investigated in three vegetation communities (heathland, sedgeland, dry sclerophyll forest) in north-east Tasmania. In all these communities, trapping success was markedly higher at trap stations with a high percentage cover of vegetation less than 50 cm high. Trapping success was also significantly influenced (P<0.01) by the presence of Rattus runways in all communities, runways of larger animals in heath, and logs in the understorey of forest. Percentage cover of vegetation greater than 50 cm high, rock cover and litter cover were not shown to influence trapping success. For population censuses per se, it may be desirable to have some latitude in trap placement within a predetermined trapping configuration, to enhance captures. However, this procedure is not recommended for studies primarily investigating habitat use by small mammals.

Three-Way Interactions: Barnacles, Limpets, and Algae in a Sonoran Desert Rocky Intertidal Zone

Field experiments and observations were used to evaluate the interactions among barnacles, limpets, and algae in a rocky intertidal community in the northern Gulf of California. Competition for space, apparently via space preemption, between the barnacle Chthamalus anisopoma and an encrusting alga of the genus Ralfsia was consistently evident. Grazing by the limpet Collisella strongiana limited algal abundance and indirectly increased the abundance of Chthamalus; no direct effect of Collisella on Chthamalus was detectable. High percent cover of Chthamalus reduced both algal and limpet abundances. Chthamalus affected Ralfsia both directly, through space preemption, and indirectly, by limiting limpet densities. In one experiment, these opposing effects were equivalent, resulting in no net effect of the removal of Chthamalus on Ralfsia. Results also indicated a negative feedback loop: removal of Chthamalus increased limpet densities, which suppressed any increase in Ralfsia, enhancing the recovery of Chthamalus. The above interactions imply a beneficial indirect effect of Ralfsia on Collisella, arising from the prevention of Chthamalus settlement by Ralfsia. Circumstantial evidence in this study and direct evidence (in Dungan 1984) suggested that predation on Chthamalus by the gastropod Acanthina angelica is also of major importance in this system. These interactions appeared to explain some aspects of temporal variation in community structure. This community was characterized by strong, highly interdependent interactions. Both direct and indirect effects of species on each other were repeatedly evident and operating on similar time scales.

The Relationship between Habitat Heterogeneity, Space Use, and Demography in a Population of California Voles

The relationships between habitat heterogeneity, space use, and demography were analyzed in a population of California voles (Microtus californicus). Live-trapping was conducted on a monthly basis from 1977 to 1981 on four grids, each sampling a different microhabitat type within a meadow. High quality habitat patches (having high percent cover of the perennial grass Elymus triticoides) were characterized by higher peak densities, more strongly female-biased sex ratios, longer average persistence (= survivorship), and higher rates of juvenile recruitment than were lower quality patches (Conium maculatum and annual grasses). For females, probability of persistence varied markedly in response to seasonal (wet vs. dry) variation in resource quality, while for males, probability of persistence was lower and constant across all seasons. The study included a period of low density (1977-1979) followed by an irruption (spring 1980) and subsequent crash in vole numbers. Persistence of females did not vary with population density, but persistence of males was inversely related to density. Females tended to aggregate in high quality areas but the distribution of males was more uniform. Females co-occurred at individual trap sites within 2-3 d trapping periods significantly more frequently than did males. In addition, the frequency of co-occurrence of females was higher in better quality habitat patches than in poorer microhabitat, whereas the frequency of co-occurrence of males was spatially unvarying. Both sexes showed an increased frequency of co-occurrence with increased density; however, co-occurrence of females was often high even at low densities, while co-occurrence of males was virtually non-existent at low densities. We believe that the responsiveness of females to both spatial and temporal variation in resource quality reflects a direct reliance on resource acquisition for reproductive success, and that their tendency to overlap intrasexually indicates a lack of strong intrasexual interference. In contrast, the lack of responsiveness of males to resource variation may reflect a relative independence from resource acquisition in seeking reproductive success, while their low co-occurrence and greater sensitivity to density variation indicates the presence of strong intrasexual interference.