Showing papers in "American Midland Naturalist in 1983"

The Secondary Chemistry and Complex Morphology of Galls Formed by the Cynipinae (Hymenoptera): Why and How?

Abstract: Oak galls formed by cynipine wasps are extremely complex and diverse structurally, histologically and chemically. Evidence suggests that the need for enemyfree space provides the major selective force molding this rich diversity, which in turn allows many species to co-occur locally in spite of highly successful attacks by natural enemies. It is proposed that the Cynipinae form mutualisms with virus or virus-like particles which work in concert with larval salivary secretions to produce galls. This ecological alliance may have engendered the adaptive shift to gall-forming from the seed-eating habit of secondarily phytophagous Hymenoptera. The role of mutualism as a driving force in evolutionary innovation may be considerable.

The response of fishes to periodic spring floods in a southeastern stream.

Abstract: Movement of fishes onto a fringing floodplain was studied by seining and trapping during five spring floods. We collected 26 species from the inundated floodplain; the known channel fauna is 42 species. Species numerically dominant on the floodplain were Fundulus olivaceus, F. notti, Gambusia affinis, Notropis welaka, N. texanus, N. roseipinnis, Lepomis macrochirus, L. cyanellus and L. marginatus. Catch-per-effort in traps was generally greatest on the upper floodplain during the day and greatest nearer the channel at night. Night activity of fishes on the floodplain was apparently low. Several species, which we term flood-quiescent forms, were common in the channel (e.g., Lepomis megalotis and Percina nigrofasciata) but did not exploit the floodplain. Activity (as catch per trap-hour) of P. nigrofasciata was negatively correlated with floodinduced turbidity. A flood-exploitative species, Notropis texanus, had higher population abundance during 3 high-flow years than in 3 low-flow years, suggesting that spring flooding may exert significant control over fish community structure. INTRODUCTION Periodic flooding is characteristic of most lotic systems. Based on channel morphology and gradient, floods may be erosive and thus potentially destructive to the stream habitat, or depositional, exhibiting "creeping flow" and being generally nondestructive to channel morphology (Welcomme, 1979). Most studies of the effects of flooding on aquatic organisms have treated erosive floods (e.g., Paloumpis, 1958; John, 1963, 1964; Greenfield et al., 1970; Seegrist and Gard, 1972; Hanson and Waters, 1974; Hoopes, 1975; Harrell, 1978), in which severe faunal disruption often occurs. Adaptations of organisms to erosive floods are either for surviving high flow rates through behavioral or morphological modifications, or for life history characteristics allowing rapid recolonization. Few studies have addressed the effects of nondestructive flooding on North American streams. Such floods occur in low gradient systems in which floods are primarily characterized by lateral expansion rather than increases in depth (Welcomme, 1979). While lateral expansion of rivers onto floodplains is best developed in tropical areas (Welcomme, 1979), many North American streams, especially in the southeastern United States, also show (or showed prior to levee construction and channelization) well-developed fringing floodplains (Viosca, 1927; Gunter, 1957; Bennett, 1958; Guillory, 1979). Such natural floodplains may be seasonally inundated. Forbes (1925) pointed out the importance of inundated floodplains as breeding grounds and foraging areas for fishes and aquatic invertebrates. Wickliff (1945) recorded movement of fishes onto an inundated floodplain. Starrett (1951) determined that certain minnows spawn in backwater areas and suggested that flooding was an important factor controlling minnow populations. Bennett (1958) believed that periodic flooding of the Mississippi and Illinois rivers was beneficial to largemouth bass populations. Guillory (1979) found that a number of Mississippi River species used inundated floodplains as

The effects of suspended silt on feeding and reproduction of daphnia pulex

Abstract: This paper reports the effect of suspended silt on the feeding and reproduction of Daphnia pulex and the impact of suspended silt and clay on freshwater zooplankton community structure. The effects of suspended silt and clay on the filtering and assimilation rates of Daphnia pulex were determined using a 14C radiotracer method. Both filtering and assimilation rates are severely depressed at even low concentrations of suspended silt and clay. Life table studies also showed population growth rate of zooplankton was significantly diminished by suspended silts and clays. The relative abundance of zooplankton varied markedly between two lakes of differing turbidity levels, the more turbid lake having a higher relative abundance of large zooplankton species. Suspended silt and clay reduced zooplankton feeding and production but probably influenced zooplankton community structure by impairing the ability of visually feeding planktivorous fish to locate their prey. INTRODUCTION Zooplankton play a pivotal role in the transfer of energy in food chains of ponds, lakes and oceans. These small herbivores feed on diffuse plant resources, thereby repackaging energy into a much more concentrated form which can be used by carnivores. There have been many studies of the feeding ecology of zooplankton (Ryther, 1954; Rigler, 1961; Burns and Rigler, 1967; Hall et al., 1976; Porter et al., 1982) and the forces which limit zooplankton populations. Still, there is debate on the relative importance of competition among zooplankton for limited food resources vs. planktivory as the dominant force limiting zooplankton population densities and structuring zooplankton communities (Brooks and Dodson, 1965; Hall et al., 1970; Lynch, 1979; Neill and Peacock, 1980; Zaret, 1980). This debate arises anew when considering turbid lakes characteristic of midwestern and southeastern North America. Such lakes often have large zooplankton in relatively high densities and such large zooplankton could result from interaction with suspended silts and clays in at least two ways. First, dissolved organic matter adsorbed to silt particles ingested by filter-feeding zooplankton could supply added nutrition sources (Marzolf, 1965). Second, suspended silt particles may serve as a refuge for zooplankton from planktivorous fish which locate prey visually (Vinyard and O'Brien, 1976; Gardner, 1981). Vinyard and O'Brien (1976) and Wright (1981) showed that increasing turbidity impairs the ability of planktivorous fish to locate prey. Buck (1956) reported production of redear sunfish (Lepomis microlophus) in low turbidity ponds was 300 times greater than in ponds with high turbidity. While the effects of turbidity on predaceous fish are documented, similar data for herbivorous zooplankton are not available. The purpose of this study is to determine the effects of suspended silt and clay on filtering rates, assimilation efficiencies, population growth and community structure of zooplankton. METHODS Algal cultures used in filtering rate and assimilation efficiency determinations were 1 Current address: Department of Environmental Science and Engineering, University of California at Los Angeles, Los Angeles, California.

Diameter distributions in even-aged stands of shade-tolerant and midtolerant tree species

Abstract: Characteristics of diameter distributions in 28 even-aged northern hardwood (Acer-Betula-Tsuga) and upland oak (Quercus spp.) stands were investigated to determine if even-aged stands of shade-tolerant and midtolerant (intermediate) species can be consistently identified without direct age determinations. The diameter distributions of midtolerant species consistently approximated a normal distribution. Those of tolerant species were highly variable, ranging from unimodal to steeply descending in form. Distributions of tolerant species that departed strongly from a unimodal form were those of stands having a large admixture of midtolerant species. Confusion with all-aged stands in such cases can be avoided if classification of age structure is based on the diameter distributions of midtolerant species. Even-aged and all-aged stands can generally be distinguished on the basis of diameter distributions, but even-aged stands cannot be consistently distinguished from multi-aged stands in which young trees are sparse or absent. In such cases, a number of direct age determinations would be necessary. INTRODUCTION Data on age structure of forest stands are often needed in ecological studies, especially for quantifying the role of natural and man-caused disturbances in forested landscapes. The only feasible nondestructive technique for direct interpretation of age structure requires the extraction of cores from trees in sample plots. This procedure is time-consuming and is not feasible when extensive areas must be inventoried. Accuracy in age determination of large trees is limited by the frequent occurrence of heart rot and by the fact that the number of rings above the butt swell does not indicate the total age of the tree. Indirect assessment of age structure has therefore been frequently attempted, of which the most promising method has been the interpretation of diameter frequency distributions. To give a reasonable indication of age structure, diameter distributions must be plotted separately for individual species from small homogeneous stands (Hough, 1932). Even-aged stands of many species typically have unimodal diameter distributions that may show varying degrees of skewness at a young age but gradually approach a more symmetric normal distribution with time (Baker, 1923; Meyer, 1930; Hough, 1932; Schnur, 1934; Nelson, 1964; Mohler et al., 1978). All-aged stands of shade-tolerant species with only light past disturbance, on the other hand, are wellknown to have steeply descending, monotonic diameter distributions that can be approximated by the negative exponential and negative power functions (de Liocourt, 1898; Hough, 1932; Assmann, 1970; Leak, 1973, 1975; Hett and Loucks, 1976; Tubbs, 1977; Lorimer, 1980). A third type of age structure may occur in stands having several age classes that may or may not be of equal prominence. Diameter distributions in such stands may vary from near normal to irregular negative exponential in form depending upon the dispersion of age classes and the degree of shade tolerance of the species (Hough, 1932; Henry and Swan, 1974; Leak, 1975; Oliver and Stephens, 1977; Harcombe and Marks, 1978; Lorimer, 1980, 1983a). Some stands of this latter type are technically uneven-aged or all-aged but nevertheless developed after heavy destruction of the overstory, and the wide range in age merely reflects the range of ages among smaller trees present prior to the disturbance (Henry and Swan, 1974; Lorimer, 1983a). In other cases, the restricted or unbalanced age distribution may be due to other external

Foraging, grooming and mate-seeking behaviors of Macropis nuda (Hymenoptera, Melittidae) and use of Lysimachia ciliata (Primulaceae) oils in larval provisions and cell linings

Abstract: The first demonstrated use of floral oils in nest cell linings and pollen provisions is reported here for the bee Macropis nuda (Melittidae). The floral oil chemistry is closely analogous to the cell-lining lipids secreted from the Dufour's glands of many other bee genera. Details of oil and pollen collection and transfer behaviors at Lysimachia ciliata are compared with those of other bee taxa. The simultaneous pollen and oil collection behaviors are reminiscent of Melitta "buzz pollination" (sensu Buchmann, 1978). Aspects of the mating biology, including hind leg posturing to advertise mating nonreceptivity, are also discussed.

Breeding Ecology of Vesper Sparrows in Corn and Soybean Fields

Abstract: The breeding ecology of vesper sparrows (Pooecetes gramineus) was studied along fencerows between corn and soybean fields in central Iowa. Territories included portions of both corn and soybean fields, usually within 80 m of the fencerow. Breeding densities were greater along more shrubby fencerows. Nesting success in corn and soybean fields was low, 9% before 15 June and 28% thereafter. Nest losses resulted primarily from agricultural operations (27 % of all nest losses) and predation (29 % ). Nest predation was higher near agriculturally nonproductive areas. Late in the season, when most of the successful nesting by vesper sparrows occurred, washes were heavily used as nest sites. Nest placement shifted seasonally, probably in response to changes in food availability and cover for nesting activities. Renestings during the middle of the breeding season were farthest from nonproductive areas. Annually, vesper sparrows produced an average of 2.8 young/pair, probably below replacement levels. Vesper sparrow breeding success likely would be greater if the number of tillage operations was reduced and crop residue was retained on the

Effect of Microhabitat Features on Habitat Use by Peromyscus leucopus

Abstract: Habitat use and selection by the white-footed mouse (Peromyscus leucopus) were examined in riparian woods and associated grassy, shrubby and limestone outcrop habitats on the Konza Prairie Research Natural Area near Manhattan, Kansas. Analysis of captures on a large, irregular grid (843 stations) demonstrated significant differential use of habitat types by P. leucopus. Selection of habitat types was related to the vertical structure of the vegetation with areas of complex vertical structure (trees with large shrubs, large shrubs without trees or trees with small shrubs) selected over those with less well-developed vertical structure (trees without shrubs, small shrubs without trees or grass). The same basic pattern persisted when microhabitat features in the immediate area of traps were examined. Use of microhabitats associated with rocks, logs, stumps and fallen trees in the riparian woods revealed greater use of areas with dense cover. The use of microhabitats associated with limestone outcrops confirmed a pattern of greater use of protected than of open areas. Patterns of habitat and microhabitat use were generally consistent with the use of habitat features to avoid predators; however, food distribution was not examined and availability of food in different sites may explain part of the use patterns. Limited observations on habitat selection by Neotomafioridana suggested that competitive interactions between P. leucopus and N. floridana were relatively unimportant in the macroand microhabitat use patterns of P. leucopus.

Effects of Fire on Nutrient Availability in a North Carolina Coastal Plain Pocosin

Abstract: Nutrient availability was monitored in recently burned and unburned blocks of a large ombrotrophic shrub-bog in Jones Co., North Carolina, U.S.A. Availability of Mg, K, P04-P, NH4-N and N03-N was significantly increased, whereas available Ca was lower in the burned area than the unburned area. Concentrations of several nutrients, particularly P04-P and N03-N, were considerably more variable spatially in the burned area. Nutrient concentrations in peat from the clipped plots were not different from those of unmanipulated areas. Bioassays using Pinus serotina revealed phosphorus deficiency in unburned peat which was ameliorated by burning.

Leaf-shredding insects as a source of dissolved organic carbon in headwater streams.

Abstract: This study investigated the importance of leaf-shredding insects as generators of dissolved organic carbon (DOC) in a headwater stream. Three common southern Appalachian shredder species (Peltoperla maria, Pteronarcys scotti and Tipula spp.) were allowed to feed on naturally conditioned leaves, and the rates at which DOC was generated were measured. DOC generation rates of actively feeding shredders ranged from 0. 2-160 ,ug C mg shredder AFDWI day-', and 62 % of this variation could be explained by organism weight. Weight-specific rates increased as body size decreased, presumably in response to an increase in weight-specific metabolic rate. DOC generation rate per individual increased as animal size increased. DOC generation increased as generation of particulate matter increased, with a mean of 60 Ag DOC produced per mg AFDW particles generated. Less than 10% of DOC generated was produced by mechanical breaking up of the leaves. The DOC generated by shredders was predominantly in the high (> 10,000 daltons) molecular weight fraction. The rates presented are underestimates of actual rates; experiments with sterilized leaves demonstrated that microbial activity during experiments with natural leaves reduced the amount of DOC accumulating in the chambers. DOC released by actively feeding shredders is a potentially significant source of DOC in a small headwater southern Appalachian stream during low flow conditions. Shredder feeding is potentially as important a source of DOC in small streams as leaching of leaf litter. INTRODUCTION Dissolved organic carbon (DOC) is an important source of organic carbon in forested headwater streams; e.g., in Bear Brook, New Hampshire, 47 % of total organic carbon inputs was in the dissolved fraction (Fisher and Likens, 1973). DOC is taken up by microbial and chemical processes in the benthos (Cummins et al., 1972; Wetzel and Manny, 1972; Lush and Hynes, 1978; Dahm, 1981), and some is exported from the system as respired CO2 (McDowell and Fisher, 1976). Previous studies of DOC in streams have dealt primarily with sources and fates of allochthonous DOC (Fisher and Likens, 1973; McDowell and Fisher, 1976; Dahm, 1981). In this study we evaluate the potential importance of DOC released by the feeding activities of leaf-shredding aquatic insects. In headwater forested streams, where leaf litter inputs are high, leaf-shredding insects are one of the dominant functional groups in the benthos (Vannote et al., 1980). In southern Appalachian streams, shredder feeding accelerates leaf decomposition, and insect feces are an important source of seston (Wallace et al., 1982a). Our goal in this study was to determine if insect feeding could also contribute significant quantities of DOC in a stream. Release of DOC by invertebrates has been documented in a number of marine Uohannes and Satomi, 1967; Johannes and Webb, 1970) and freshwater groups Uohannes and Webb, 1970; Hargrave, 1971). Rates of release vary as a function of animal size and feeding habits: Hyallela azteca released only 5% of ingested calories (Hargrave, 1971) while Palaemonetes pugio released 33% of ingested organic carbon

Early Plant Succession on the Muddy River Mudflow, Mount St. Helens, Washington

Abstract: Long-term plant succession studies using permanent plots were initiated on the Muddy River mudflow in the Mount St. Helens area of southeastern Washington. Plant cover and geomorphic surface were observed on 126 circular plots (250 M2). One hundred and eight species were identified and categorized based on oc- currence in eight microsite types. Herb, shrub and tree seedling cover decreased with increasing distance from forest edges and with decreasing distance from the base of Shoestring Glacier. Greatest plant cover occurred on roadbanks, around bases of stumps and along streams.

Structural characteristics and biomass production of two Illinois bottomland forests.

Abstract: Structural characteristics and biomass production of two Illinois bottomland forests with contrasting hydrological and nutrient regimes were investigated. One forest had stagnant floodwaters (still-water site) and was flooded longer than the other site, which was flooded mainly in the spring when the nearby river overflowed its bank (flowing-water site). Both were flooded with nutrient-rich waters although the relative concentrations of N, P and cations (Ca, K, and Mg) differed between the two sites. The still-water forest had a higher stem density (459/ha vs. 423/ha), higher basal area (41.1 m2/ha vs. 32.1 m2/ha), more tree species (12 vs. 6) and taller trees (34.1 m vs. 24.9 m) than the flowing-water forest. Basal area, stem density and complexity of the still-water forest were similar to those of more southerly bottomland forests, but these same structural characteristics for the flowing-water forest were lower. Average growth per tree was lower in the flowing-water forest than in the still-water forest (0.7-7.3 cm2/yr vs. 7.9-24.6 cm2/yr). Annual litterfall was also lower in the flowingwater forest (607 g/m2 vs. 650 g/m2), but not significantly. Total aboveground biomass production at the still-water site (960 g m-?yr-1) was almost 1.5 times higher than at the flowing-water site (668 g m-?yr-1), due mainly to the very low wood production in the latter (177 g m-?yr-1 vs. 424 g m-?yr-1). Biomass production of the still-water forest was high compared to other still-water bottomland forests in the United States while biomass production of the flowing-water forest was approximately half that of other flowing-water forests. The low production of the flowing-water forest does suggest that not all floodplain forests are highly productive.

The Effect of Fire on an Ungrazed Western Montana Grassland

Abstract: On 28 June 1977 a hot wildfire burned part of a species-rich foothills grassland dominated by Festuca scabrella, F. idahoensis and Agropyron spicatum. We sampled plant species cover in paired stands, on and off the burn, during 1977 and 1978 to determine the initial impact of the fire, and during 1980 to document recovery after 3 years. Grass cover decreased on the burn due primarily to a sharp drop in the cover of the two dominant fescues. Forb cover increased. Moss and lichen cover dropped greatly. Much of the difference in species response was related to plant growth form and phenology. Large bunches of F. scabrella were more seriously damaged than small ones, indicating long intervals between fires are detrimental to the species when fire does return. At burned sites, afternoon soil temperatures were higher and near-surface soil moisture was lower. Three years after the fire, cover of most vascular species was similar in burned and unburned stands. Festuca idahoensis had recovered completely. Festuca scabrella had increased but was still well below unburned levels. Total moss cover on the burn was nearly that on unburned sites, but the species composition was greatly altered. Lichens were still reduced. The stability of the grassland in relation to fire is discussed.

Initial recovery of subalpine vegetation on Mount St. Helens, Washington.

Abstract: A network of permanent plots has been established on the subalpine slopes of Mount St. Helens. Plants in sites receiving only tephra or thin mud deposits survived the 18 May 1980 eruption and re-established themselves by late summer. Richness and cover on these substrates increased dramatically by 1981. Sites receiving thick cold mudflows have little vegetation after two growing seasons, and the few scattered individuals encountered are residual survivors, not seedlings. Subalpine sites destroyed by the directed blast, debris flow or pyroclastic flows had no surviving vascular plants and have yet to be recolonized. Such sites will require import of organic debris, nitrification and seed invasion for recovery to commence. Community analysis shows that subalpine herb composition is changing on all sites and that the magnitude of change, except on totally devastated sites, is proportional to the magnitude of the initial impact. Based on two seasons of observations, future changes in species number and cover are projected.

A retrospective view of old-field succession after 35 years [North Carolina].

Abstract: In 1947 I began my doctoral studies to determine the causes of early old- field succession in the North Carolina Piedmont. I present here a review of the research that led me to undertake those studies and a synopsis of the research on patterns and mechanisms of old-field succession which followed. Although a few species are ubiq- uitous among old fields, the patterns and rate of species replacement vary considerably among and within regions. In few areas are stages as distinct or progress so rapid as in North Carolina. I expect the mechanisms are also varied and suggest that factors such as site history, farming practices and seed availability have been underrated. In general, much of the variation in old-field composition appears to be related to varia- tions among species in germination requirements and life histories. PRE- 1947 RESEARCH In the autumn of 1947, as a graduate student at Duke University, I began working on the causes of old-field succession in North Carolina. The sequence of species in- vading and dominating abandoned farmland in North Carolina had been determined by Crafton and Wells (1934) and Oosting (1942) with little disagreement. Crabgrass (Digitaria sanguinalis (L.) Scop.) usually occupies fields in the late summer and autumn following the last cultivation. Horseweed (Erigeron canadensis L.) dominates fields the 1st year of abandonment, followed in turn by aster (Aster pilosus Willd.) and broomsedge (Andropogon virginicus L.) in the 2nd and 3rd years. Broomsedge fields are invaded by pines of several species, which usually form a complete canopy in 10 or 15 years. After one generation pines are replaced by hardwoods. Dr. Oosting admitted (pers. comm.) that although he knew the sequence of species in early old-field succession, he did not know what caused these distinct and fast changes and challenged me to find the causes. Clements (1916) had proposed that pioneer species change the environment and make it more suitable for species that invade by increasing the humus in the soil, pro- viding shade and improving water and mineral conditions. This idea was widespread and generally accepted until the 1940s as the major cause of succession. Crafton and Wells (1934) found that one of the causes of old-field succession is competition for water. Coile (1940) and Oosting and Kramer (1946) had investigated the role of water and light in the replacement of pines by hardwoods. At about the same time the idea that one plant may produce some chemicals which are inhibitory or toxic to other plants (allelopathy) had been advanced by Davis (1928), Went (1942), Bonner and Galston (1944) and others. Such toxins could be the cause of one species replacing another in the old-field sequence. Perhaps horseweed produces a toxin that delays the invasion of aster, or aster produces a toxin that helps eliminate horseweed from the old- field succession in North Carolina. Drew (1942) worked out the sequence of species on abandoned farm fields in Missouri and speculated on the causes of variations from field to field. He concluded that the only event that correlated with the differences was what the last crop had been. From my research (Keever, 1950) I concluded that the early dominants are largely determined by the capability of their seeds to germinate at the time of year a suitable habitat is available. After the germination of seeds, the entrance and exit of each

Evidence of Plant Succession on Granite Outcrops of the Georgia Piedmont

Abstract: Successional changes are taking place in the vegetation of certain "island communities" on granitic rock outcrops in the Lithonia, Georgia, area (Piedmont Plateau). The floristic composition and maximum soil depths of 34 communities, first studied in 1957, were re-examined in 1968 and 1976-1978. Maximum soil depth tended to increase over time. Sixteen of the 34 communities studied showed successional changes in floristic composition, confirming the earlier hypothesis that lichen-annual, annual-perennial and herb-shrub communities represent seral stages as soil depth increases. There are characteristic plants and maximum soil depths for each stage, with overlapping depth ranges. Diamorpha communities, which occur on the shallowest soils, have remained unchanged floristically and maximum soil depths have changed only slightly. With 1-12 cm increases in soil depths, three lichen-annual communities became annual-perennial communities, four annual-perennial communities progressed to an herb-shrub or shrub-tree stage, and one herb-shrub community became a shrubtree community. Shrub-tree communities may represent an edaphic climax subject to periodic regression to earlier seral stages. INTRODUCTION Plant communities on exposed granitic rock to the E and SE of Atlanta, Georgia, and the life histories of characteristic species of these communities have been the subject of scientific study for many years. McVaugh (1943) included the portion of the Piedmont near Atlanta in his comprehensive study of the vegetation of granitic flatrocks in the southeastern United States and suggested two types of succession on rock surfaces, mat formation and succession in soil-filled depressions in the exposed rock. In 1964, Burbanck and Platt published an analysis of the vegetation of 40 communities of plants located on three geologically similar granite outcrops. The communities were termed "island communities" since each occurred on soil in depressions surrounded by exposed rock. These communities were classified into four types based on maximum soil depth and type of vegetation in each community. Burbanck and Platt suggested that the four types of communities represented seral stages related to the edaphic conditions; the greater the soil depth, the more advanced was the seral stage. Since the original observations were made in 1957, 1958 and 1959, the communities have been examined periodically and data collected pertaining to depth of soil and floristic changes to determine whether or not plant succession is taking place and whether the four types of communities represent seral stages. This paper presents some of the results of a 22-year study of communities on three different granite outcrops in the Georgia Piedmont near the town of Lithonia, SE of Atlanta, Georgia. MATERIALS AND METHODS Burbanck and Platt (1964) selected 40 communities for study in 1957: 17 on Arabia Mountain, 16 on Rock Chapel Mountain and seven on Mount Rollaway. These communities occurred in irregularly circular or elliptic depressions in exposed rock surfaces, ranged from 1.3 to 56.9 m2 in area but usually had a diam of 5 m or less, and the depth of soil ranged from 2-50 cm at the deepest part of each island community. Communities were chosen which had intact bottoms; that is, there was no evidence of cracks or crevices in the rock beneath the community. Four types of communities were recognized by Burbanck and Platt (1964) based on characteristic vegetation and maximum soil depth: diamorpha (a succulent annual) (2-9 cm); lichen-annual herb (7-15 cm); annual-perennial herb (14-39 cm); herb-shrub

A Retrospective View of Old-field Succession after 35 Years

Abstract: In 1947 I began my doctoral studies to determine the causes of early old- field succession in the North Carolina Piedmont. I present here a review of the research that led me to undertake those studies and a synopsis of the research on patterns and mechanisms of old-field succession which followed. Although a few species are ubiq- uitous among old fields, the patterns and rate of species replacement vary considerably among and within regions. In few areas are stages as distinct or progress so rapid as in North Carolina. I expect the mechanisms are also varied and suggest that factors such as site history, farming practices and seed availability have been underrated. In general, much of the variation in old-field composition appears to be related to varia- tions among species in germination requirements and life histories. PRE- 1947 RESEARCH In the autumn of 1947, as a graduate student at Duke University, I began working on the causes of old-field succession in North Carolina. The sequence of species in- vading and dominating abandoned farmland in North Carolina had been determined by Crafton and Wells (1934) and Oosting (1942) with little disagreement. Crabgrass (Digitaria sanguinalis (L.) Scop.) usually occupies fields in the late summer and autumn following the last cultivation. Horseweed (Erigeron canadensis L.) dominates fields the 1st year of abandonment, followed in turn by aster (Aster pilosus Willd.) and broomsedge (Andropogon virginicus L.) in the 2nd and 3rd years. Broomsedge fields are invaded by pines of several species, which usually form a complete canopy in 10 or 15 years. After one generation pines are replaced by hardwoods. Dr. Oosting admitted (pers. comm.) that although he knew the sequence of species in early old-field succession, he did not know what caused these distinct and fast changes and challenged me to find the causes. Clements (1916) had proposed that pioneer species change the environment and make it more suitable for species that invade by increasing the humus in the soil, pro- viding shade and improving water and mineral conditions. This idea was widespread and generally accepted until the 1940s as the major cause of succession. Crafton and Wells (1934) found that one of the causes of old-field succession is competition for water. Coile (1940) and Oosting and Kramer (1946) had investigated the role of water and light in the replacement of pines by hardwoods. At about the same time the idea that one plant may produce some chemicals which are inhibitory or toxic to other plants (allelopathy) had been advanced by Davis (1928), Went (1942), Bonner and Galston (1944) and others. Such toxins could be the cause of one species replacing another in the old-field sequence. Perhaps horseweed produces a toxin that delays the invasion of aster, or aster produces a toxin that helps eliminate horseweed from the old- field succession in North Carolina. Drew (1942) worked out the sequence of species on abandoned farm fields in Missouri and speculated on the causes of variations from field to field. He concluded that the only event that correlated with the differences was what the last crop had been. From my research (Keever, 1950) I concluded that the early dominants are largely determined by the capability of their seeds to germinate at the time of year a suitable habitat is available. After the germination of seeds, the entrance and exit of each

Survivorship and parasite-induced host mortality among mosquitofish in a predator-free, North-Carolina cooling reservoir.

Abstract: Survivorship of mosquitofish infected with the pseudophyllidean tapeworm Bothriocephalus acheilognathi was significantly reduced as compared with uninfected mosquitofish when fish were held at temperatures of 20, 25 and 30 C. Survivorship of infected and uninfected fish was also significantly reduced as water temperatures were increased to 25 and 30 C. When mosquitofish were maintained at 25 C, larger individuals with lower parasite densities survive longer than smaller individuals with higher densities of the cestode. Pearson correlation and multiple regression analyses of survival time of Gambusia affinis on density of Bothriocephalus acheilognathi and total host length indicate that survivorship is a function of parasite density and host size. Certain demographic characteristics of mosquitofish populations in a system devoid of piscivorous predators (but with B. acheilognathi) were compared with those in a system having piscivorous predators (but without B. acheilognathi). Random samples of mosquitofish taken monthly from the two systems revealed no significant differences in either sex ratios or in mean lengths of male or female mosquitofish. The Krumholz (1963) predation hypothesis would predict otherwise, to wit, that sex ratios in the predator-free system should be 1:1 (with predators, sex ratios should be approximately 1 male: 2 females) and that both males and females should be significantly larger than males and females in a system possessing a full complement of piscivorous fishes. It is hypothesized that similarities among demographic features of mosquitofish populations in the two systems investigated in the present study are the result of parasite-induced, size-selective host mortality in the predator-free system on the one hand and of predation pressure from piscivorous fishes on the other.

Seasonal Changes in Coyote Food Habits as Determined by Fecal Analysis

Abstract: Feces were analyzed to determine the food habits of coyotes (Canis latrans) in Cuyamaca Rancho State Park, San Diego Co., California. Of 748 food items identified from 223 scats, mammals made up 53 %, vegetation 23 %, arthropods 9%, reptiles 1 %, birds 1 % and miscellaneous items 3 %. Percent relative frequency of mammalian food items decreased significantly from winter (78%) to summer (52 %). Conversely percent of arthropod remains in summer scats ( 1 o%) increased significantly from winter scats (0%). Percent occurrence of vegetation in feces also increased significantly from winter (12%) to summer (22 %). Observations of coyotes did not vary significantly between seasons. These results suggest that coyotes feed opportunistically in Cuyamaca Rancho State Park. INTRODUCTION Past studies of coyote (Canis latrans) food habits (Bond, 1934; Murie, 1940, 1951; Ferrel et al., 1953; Fichter et al., 1955; Korschgen, 1957; Gipson, 1974; Holle, 1978; Johnson and Hansen, 1978; Litvaitis and Mautz, 1980) prompted some authors to categorize the feeding behavior of coyotes as opportunistic (Murie, 1945; Fichter et al., 1955; Nellis and Keith, 1976; Bekoff, 1977; Litvaitis and Shaw, 1980), whereas others suggested their feeding was highly selective (Clark, 1972; Johnson and Hansen, 1979; Todd et al., 1981). Seasonal variation in the food habits of coyotes has been welldocumented (Ferrel et al., 1953; Fichter et al., 1955; Korschgen, 1957; Bowen, 1981), but limited data are available for southern California. The purpose of this study was to examine seasonal fluctuations in the number of coyotes in relation to corresponding changes in their food habits. STUDY AREA East Mesa is located in Cuyamaca Rancho State Park, San Diego Co., Calif., at an elevation of 1525 m. This area consists of extensive upland meadows, intermixed with stands of oak (Quercus kelloggii and Q agrifolia) and pine (Pinusjeffreyi) and is surrounded by dense chaparral. Bowyer and Bleich (1980) provide a more complete description of this area. METHODS Scats were collected along a 8.2-km dirt road on East Mesa on 268 days from June 1977 throughJanuary 1979. Sightings of 278 coyotes occurred along this fixed transect throughout the sampling period. Scats were stored in paper bags, and location, date and method of scat identification were recorded. Coyote feces were identified by their characteristic morphology and the presence of coyote tracks nearby. For laboratory analyses, scats were placed in nylon stockings and thoroughly rinsed under tap water. Remains were spread across a dissection pan and carefully examined with a dissection microscope for food items. Additionally, four or five random points were examined for food items in each pan. Mammalian species were identified from hair morphology as Present address: Center of Environmental Sciences, Unity College, Unity, Maine 04988.

Drought-induced changes in crayfish populations along a stream continuum.

Abstract: Crayfish populations in 2ndand 5th-order streams in NE Georgia varied significantly between sites within 1 year and between years. The 1st year had normal rainfall and the second a severe drought. Of two crayfish species that inhabit the drainage the burrowing species (Cambarus latimanus) showed no significant changes, whereas the nonburrower (Procambarus spiculifer) exhibited large drought-induced population changes, including reductions in adult population densities, resident densities and body size, an alteration in the reproductive timing and an increase in the number of juveniles in the population. I hypothesize that many of the changes in P. spiculifer resulted from their size-dependent preference for deep water sites, and that the reduction of these sites during the drought led to adult emigration and increased predation on larger adults. The distribution of population variables between study sites exhibited the same depth-dependent distribution, the shallower reaches having small populations of small adults and large numbers of juveniles. As the habitat depth decreased during the drought, the above subpopulation properties adjusted spatially, apparently following the physical conditions to which they were adapted. These results agree with the stream continuum concept.

Observations on the Natural History of the Blue Sucker (Cycleptus elongatus Le Sueur) in the Neosho River

Abstract: Populations of blue suckers in the Neosho River in Kansas were sampled by electrofishing during the spring and summer of 1976 and 1977. Spawning occurred in deep riffles (1-2 m) with cobble and bedrock substrates in May at water temperatures of 20-23 C. By August, juveniles averaged 125 mm in length. Mature females reach greater maximum ages, weights and lengths (9 years, 4.1 kg, 763 mm T.L.) than males (7 years, 3.7 kg, 749 mm T.L.). In general, adult females were larger than adult males. Condition coefficients vary slightly with time of year. Only a few juveniles were captured, but young blue suckers occupied shallower and less swift water than adults. Laboratory stream observations confirm a preference for smooth substrates in swift current. Food of adults and young consisted primarily of insect larvae and plant material. Blue suckers seem limited by habitat, especially during spawning. INTRODUCTION The blue sucker, Cycleptus elongatus Le Sueur, is distributed from Montana to Wisconsin and Pennsylvania S to Kentucky, the Gulf of Mexico, Texas and northern Mexico (Alvarez, 1970; Brown, 1971; Clay, 1975; Douglas, 1974; Eddy, 1969; Hubbs, 1957; Smith-Vaniz, 1968). It is found in deep reservoirs (Carlander, 1969; Jenkins, 1953), but its principal habitat is the Mississippi and Missouri rivers and their largest tributaries (Pflieger, 1971, 1975). It also occurs in the Pearl and Rio Grande rivers and tributaries (Contreras and Rivera, 1972). The blue sucker is considered to be one of the finest of the freshwater food fishes and perhaps the best of the suckers (Coker, 1930; Forbes and Richardson, 1920). It was once an important part of the commercial catch of the Mississippi drainage. In 1899, the Mississippi catch was nearly 1 million kg (Coker, 1930). Today it is scarce in commercial catches. Despite its former abundance commercially, little natural history information about blue suckers has been available (Cross, 1967; Harlan and Speaker, 1956; Miller and Robison, 1973; Pflieger, 1975; Trautman, 1957) and information on age and growth was based on relatively few specimens (Carlander, 1969). Recently, Gilbert (1980) presented North American distributional information and Rupprecht and Jahn (1980) discussed size, growth, reproduction and food habits for Mississippi River blue suckers. We were able to accumulate information on habitat and spawning and complementary data on ages and growth and food habits for blue suckers in the Neosho River. METHODS The Neosho River, a tributary to the Arkansas River, drains southeastern Kansas, southwestern Missouri and northeastern Oklahoma. Our collections were from the Neosho mainstream in Labette Co. (juveniles), Lyon Co. (juveniles) and Woodson Co. (adults, spawning riffle) in Kansas. Fish were collected from early April through October in 1976 and 1977 by electrofishing with either a boom-type boat or backpack electrofisher (both D. C.). Blue suckers are very vulnerable to electrofishing, often remaining stunned for minutes after being shocked. Generally, the most effective method was to let the boat drift through deep riffles (1-2m) and return quickly upstream to net stunned fish. In shallow riffles, especially over bedrock, the backpack electrofisher was used with set seines to capture juveniles. l Present address: CSA, Natural Sciences, University of Michigan, Ann Arbor 48109.

Contributions to the flora of the Red Lake Peatland, northern Minnesota, with special attention to Carex

Abstract: The Red Lake Peatland, situated in N-central Minnesota, is the largest continuous mire in the northern portion of the contiguous United States. It consists of a mixture of ombrotrophic bogs and minerotrophic fens organized into a complex of highly distinctive landforms, including open bogs, wooded bogs, Sphagnum lawns, strings, flarks, fen-pools and wooded islands. The bogs are poor in species and occupy acid sites with water poor in mineral salts; the minerotrophic areas are floristically richer and can be divided into poorand rich-fen sites. Ditching and roadbuilding in certain portions of the peatland have produced drastic changes in the vegetation and landscape as a result of obstructed water tracks flooding upstream and drying out downstream. The peatland, which occupies a large area of gentle slope and poor drainage, has a flora that is relatively impoverished. In all, 331 plant taxa were recorded from the mire, including 195 vascular plants, 67 bryophytes and 69 lichen taxa. Members of the Cyperaceae account for 23 % of the vascular flora, and the largest genus in the mire is Carex with 29 species. Each landform feature is distinctive in its floristic composition, and the vascular and nonvascular taxa associated with the different physiographic features are discussed. This paper provides an account of Carex in the peatland and discusses the differential response by members of the genus to gradients of nutrition, shading and hydrology. Some carices grow best under acid conditions, thus frequenting ombrotrophic and poor-fen sites, whereas other species grow best in rich-fen sites. Carex species useful in separating areas of ombrotrophy from those of poor fen are indicated, as are those carices that serve as obligate rich-fen indicators. The floristic similarities between the Red Lake Peatland and 14 other peatlands in North America and northern Europe are discussed, and the ombrotrophic bog flora of the Red Lake Peatland is compared to the bog floras of the Hudson Bay lowlands and northern Fennoscandia.

Presettlement Vegetation of Hardin County, Texas

Abstract: Forest and prairie vegetation of Hardin County, Texas, at the time of European settlement, was mapped using records of the original land surveys. We recognized 11 plant communities that resemble either modern communities or presettlement communities elsewhere on the Coastal Plain of the southeastern United States. Prairie was never extensive and now occupies only 50% of its presettlement area. Beech-magnolia forest, often cited as the climatic climax for the region, appears never to have been extensive in Hardin County. Pines were important components of virtually all communities.

Sexual Selection, Body Size and Sex-related Mortality in the Cicada Magicicada cassini

Abstract: Male periodical cicadas (Magicicada cassint) were collected from a chorusing center near Lawrence, Kansas. Males in copula were significantly larger than males from the same population that were not in copula. Cicadas were offered to captive house sparrows in an aviary. The sparrows showed no consistent preference with regard to cicada size, although they did select females in preference to males. Birds may discriminate because females are more nutritious or they may avoid males which produce a "disturbance squawk" when handled.

Ants, Extrafloral Nectaries and Herbivory on the Passion Vine, Passiflora incarnata

Abstract: A temperate species, Passiflora incarnata, of the predominately tropical family Passifloraceae, possesses two sets of extrafloral nectaries which are visited by five species of ants. In an old field, plants with the extrafloral nectaries removed attracted fewer ants, experienced greater herbivory and produced fewer fruits than plants with extrafloral nectaries intact. The number of ants per plant was positively correlated with the number of extrafloral nectaries and negatively correlated with the percent herbivory.

Orientation and flight behavior of a Neotenic Salamander (Ambystoma gracile) in Oregon

Abstract: Neotenic Ambystoma gracile in lakes containing predatory trout was less abundant and less active than in lakes not containing fish. I quantified flight behavior in two populations, one exposed to fish and one not exposed to fish, focusing on direction faced and direction of flight with respect to lake morphology, and burrowing behavior at the end of the flight movement. I investigated relationships among behavior, water depth and substrate. Independence among behavioral alternatives was also evaluated. Both populations displayed significantly nonrandom behavior; the two populations differed in most behavioral components. Both populations faced toward deep water more often than could be expected by chance. In the absence of fish, 96 %o of the salamanders responded to simulated attack by moving into deeper water or by burrowing into the substrate. In the presence of fish, flight into shallower water was more frequent than expected by chance; alternatives of flight direction were dependent upon water depth in large (older) salamanders. Though burrowing for refuge was less frequent in the population exposed to fish, frequency of burrowing increased with water depth. Different frequencies of flight behaviors in the two populations are responses to differential predation pressure.

Nest Box Use by Cavity-nesting Birds

Abstract: Nest boxes were investigated for use by cavity-nesting birds at the Carey Run Sanctuary, Garrett Co., Maryland. These boxes provided nesting sites for the eastern bluebird (Sialia sialis), house wren (Troglodytes aedon) and tree swallow (Iridoprocne bicolor). Boxes at the Beltsville Agricultural Research Center, Prince Georges Co., Maryland, provided sites for the eastern bluebird, house sparrow (Passer domesticus) and tufted titmouse (Parus bicolor). Twenty-four box and habitat variables were measured at each location. Six variables were used in discriminant function analysis to segregate the boxes used by the three bird species at Carey Run. Bluebirds tended to use boxes where herb height was less than at boxes used by house wrens or tree swallows. Distance to nearest tree, sapling and shrub, and distance and dbh of the nearest tree in front of the box were least at boxes used by house wrens and greatest at tree swallow boxes. Bluebird boxes were intermediate. A discriminant function model developed for Carey Run was used to classify nest boxes at Beltsville. About 81 % of the eastern bluebird nest boxes, the species common to both sites, were classified correctly at Beltsville. Use of nest boxes by the eastern bluebird can be enhanced by placing them in the correct habitat configuration. Discriminant function analysis could be a useful management tool for evaluating nest box locations prior to undertaking an extensive nest box program. INTRODUCTION The eastern bluebird (Sialia sialis), a cavity nester, relies on woodpeckers and natural forces to create its nest cavities (Zeleny, 1976). The supply of nest sites available to bluebirds has declined owing to snag removal during agricultural and silvicultural practices, to use of treated fence posts that do not develop cavities, and to competition with introduced species, e.g., the starling (Sturnus vulgaris) and the house sparrow (Passer domesticus). The loss of nest sites has drastically reduced bluebird populations (Zeleny, 1976). To encourage bluebird nesting, nest boxes have been constructed and placed in open and semi-open areas, forming bluebird "trails." Bluebirds and other cavity nesters have successfully used these boxes to raise and fledge young; however, little quantitative information is available on the influence of location on use of boxes by different cavity nesters. The objectives of this study were (1) to determine what differences exist between nest boxes and habitat used by cavity nesters, and (2) to evaluate the ability of a multivariate statistical model developed from data collected in one physiographic region to predict box use in another physiographic region. STUDY AREA We studied nest boxes on trails located in two physiographic provinces of Maryland, the Allegheny Plateau and the Piedmont. One trail was located at the Carey Run Sanctuary on the Allegheny Plateau in rural eastern Garrett Co. (39037'N, 79008 'W, elevation 756 m). The Sanctuary is composed of 65.6 ha of abandoned fields and pastures, orchards, pine (Pinus strobus, P. resinosa) plantings and mixed hardwoods. Forest species include white (Quercus alba) and red (Q. rubra) oak, sugar maple (Acer saccharum) and some hemlock (Tsuga canadensis). Hawthorn (Crataegus sp.) shrubs and black locust (Robinia pseudoacacia) saplings are scattered throughout open areas. The sample at Carey Run consisted of 51 nest boxes erected in the early 1960s in open fields 1 Contribution No. 1355-AEL, Center for Environmental and Estuarine Studies, University of Maryland.

Ecological Relationships of Three Co-occurring Mantids, Tenodera sinensis (Saussure), T. angustipennis (Saussure), and Mantis religiosa (Linnaeus)

Abstract: Timed observations of Tenodera sinensis (Saussure) and censuses of it and two other species of mantids, T angustipennis (Saussure) and Mantis religiosa (Linnaeus), were made in the summer and autumn of 1981. Differences among these three similar species reduce niche overlap in a shared habitat. Height in the vegetation differed significantly between M. religiosa and Tenodera species but not between the two congeners. Earlier hatching time of T. sinensis reduces nymphal size overlap with its congener, whereas M. religiosa is spatially separated from both Tenodera spp. There were different degrees of emigration and oviposition between M. religiosa and Tenodera spp. on a censused field plot. Tenodera sinensis spent most of its time inactive, with feeding, grooming and changing of location accounting for progressively lower proportions of the time budget. Tenodera sinensis fed at higher sites in the vegetation more often than at lower ones. The proportion of green morphs, as opposed to brown, was also larger high in the vegeta-