Showing papers in "American Midland Naturalist in 1978"

Reproduction of chaparral shrubs after fire: a comparison of sprouting and seeding strategies

Abstract: The relative ability of sprouting and nonsprouting chaparral shrubs to recover from fire was studied by examining popula- tion of congeneric pairs of species in burned and adjacent unburned areas. The pairs of species selected, with the nonsprouting species named first, were Arctostaphylos glauca ? A. glandulosa and Ceanothus greg- gll - C. leucodermls. Data were also obtained on certain associated species, particularly Adenostoma fasclculatum. The numbers, sizes and condition of the component species at each of the sites were measured. Both sprouting and nonsprouting species showed vigorous recovery from fire. It seemed likely that the burned stands would eventually reach a state of development comparable to that shown in the preburn stand without any significant shifts in composition Mortality of shrubs resulting from the fire was complete for nonsprouters but varied in sprouting species. In some there was essentially no mortality, while in others, especially Adenostoma, it was rather high. Seedling establish- ment in the shrub species varied markedly and seemed to be correlated with the degree of fire-caused mortality. A profound difference was observed in the life histories of the two nonsprouting shrubs. Whereas Ceanothus greggll produced a very high number of seedlings after fire, Arctostaphylos glauca produced substan- tially fewer. A comparison of the density-size distribution of live and dead stems indicated that C. greggll suffers high mortality early in suc- cession, but A. glauca loses very few individuals even after 90 years without fire. In light of these results a model is proposed which we be- lieve explains the adaptive significance of the obligate-seeding strategy in the southern California chaparral.

The dynamics of crayfish and their role in ecosystems.

Abstract: An understanding of the population dynamics of crayfish and their trophic position is critical to understanding energy transformation in lakes. In many lakes crayfish dominate the annual production of the benthic biomass, at times reaching mean biomass values of 1000 1400 kg/ha and numerical densities of 15/m2. Density determines the rate of growth of various populations and determines reproductive capacity, age at maturity and life span. For Orconectes virilis, within the lakes we studied, population stability was mostly due to the short lag between a change in population density and an adjustment in fecundity. As a result, these populations appear to be self-regulated through density-dependent control of brood stock size. In Orconectes virilis, annual production was a function of mean annual biomass. Examination of available data on the ratio between other species showed them to fall within the same range as O. virilis. It seems that the evolutionary strategy governing crayfish biomass replacement and energy turnover has remained essentially unchanged. As regards their role in the community, crayfish do not fit the trophic level concept. Attempts to quantify their food habits show them to be polytrophic and a key energy transformer between various trophic links through utilization of all the trophic levels in lakes. Because of the multiple trophic roles of the crayfish, a comparison with the bioenergetics of various freshwater crust?cea is difficult. Crayfish may be most important in lakes with low phytoplankton production. In such lakes detritus and benthic algae, both of which are ingested by the crayfish, are important sources of overall energy flow. Since crayfish also function as major predators on the benthos, they most likely contribute to the stability of lake communities by interacting with a whole subweb of species ranging from large benthic invertebrates and submerged higher aquatics to the periphytic microcommunity. Hence, crayfish act as an important mechanism contributing to the regulation of most production processes and most specifically to the regulation of benthic production available to fish. In low nutrient lakes, because of their biomass dominance and functional role, crayfish greatly surpass the usual role assigned to them from their occurrence in fish diets. Manipulation of the benthic food chain would seem to be the most appropriate strategy to increase the fish production of such lakes. However, a greater appreciation of the complexity of the trophic organization of such food webs is necessary before such modifications can be attempted. 1 A contribution under Dingell-Johnson Project F-30-R, Michigan. 2 Present address: Department of Biology, Lakehead University, Thunder Bay, Ontario, Canada.

The Role of Aquatic Invertebrates in Processing of Wood Debris in Coniferous Forest Streams

Abstract: A study of the wood-associated invertebrates was undertaken in seven streams of the Coast and Cascade Mountains of Oregon. The amount of wood debris was determined in terms of both weight and surface area. Standing crop of wood per unit area decreases with increasing stream order. Invertebrates associated with wood were functionally categorized and their biomass on wood determined. Major xylophagous species were the caddisfly (Heteroplectron californicum), the elmid beetle (Lora avara) and the snail (Oxytrema silicula). Standing crop of these species is greater on wood in the Coast Range than in the Cascades, which is attributed to species composition of available wood debris. The density of L. avara was strongly correlated with the amount of wood available irrespective of stream size within a drainage. The standing crop of invertebrates was about two orders of magnitude greater on leaf debris than on wood. A potential strategy for wood consumption, based on microbial conditioning, is presented. The data are used to develop a general scheme of wood processing by invertebrates in small stream ecosystems. Their impact is similar to that of invertebrates which process leaf litter in terrestrial and aquatic environments when the full decomposition cycle of wood debris is considered. INTRODUCTION The allochthonous inputs to streams in western coniferous forests include coniferous needles, deciduous leaves and woody material, ranging in size from small twigs and bark to large logs. The amount of fallen wood in these streams can be extremely large. Froehlich (1973) estimated that in one watershed of old-growth douglas fir (Pseudotsuga menziesii) the standing crop of wood debris (pieces larger than 10 cm diam) was more than 15 kg/m2. The standing crop of small debris in the same stream was 1.08 kg/m2 (Sedell et al., 1974). In view of the quantities of woody material in these streams, it is apparent that wood has a significant role in energy flow, nutrient dynamics, stream morphology and in shaping the biotic community of these lotic ecosystems. Although stream ecologists have emphasized the importance of allochthonous debris as the food base for stream invertebrates, most previous studies are based on leaf inputs (Hynes, 1970; Cummins et al., 1973; Boling et al., 1974). Current literature on aquatic invertebrate communities inhabiting logs or inundated trees has emphasized the exploitation of these sites as habitats for attachment or surfaces for grazing of periphyton (Claflin, 1968; Nilsen and Larimore, 1973; McLachlan, 1970) rather than as allochthonous energy and nutrient inputs to the aquatic system. The present study is a preliminary investigation of the wood component in coniferous stream ecosystems of western Oregon and of the role of invertebrates in the biological processing or degradation of wood. The objectives were to survey the fauna associated with wood in streams and to determine some of the interactions between the fauna and the wood substrate. In order to develop generalizations on the invertebrate-wood interactions, we chose to compare large and small streams in two different areas rather than to investigate one site in detail.

Effects of Stand Composition on Insect Visitation in Two-Species Mixtures of Hieracium

Abstract: I investigated the effects of host plant distribution on the host plant choice of flower-visiting insects in mixed stands of the hawkweeds Hieracium aurantiacum L. and H. florentinum All. The way in which pollinators divide their visits among simultaneously blooming plant species determines the outcome of plant competition for pollinators, which may affect community structure. Although the hawkweeds are apomictic, these stands are simple communities that embody many of the assumptions of published models concerning the effects of stand composition on insect foraging. Existing theory suggests that visitation on one of two competing species should increase with its proportion in the stand. Visitation on H. aurantiacum follows this relationship, but H. florentinum receives more visits with H. aurantiacum present than when it blooms alone. Extension of this result to other, non-apomictic species implies that a species may occasionally be benefitted by the presence of an apparent competitor. I propose a tentative explanation based on pollinator inconstancy and foraging habitat selection, and suggest some possible effects of these phenomena on community structure.

Succession and Stratification of Aquatic Insects Inhabiting the Leaves of the Insectivorous Pitcher Plant, Sarracenia purpurea

Abstract: Greenhouse experiments and field collections were used in investigating the ecological relationships of three species of Diptera, Blaesoxipha fletcherl (Aldrich) (Sarcophagidae), Wyeomyla smlthll (Goquillett), (Culicidae) and Metrlocnemus knabl Coquillett (Chironomidae), which inhabit the digestive fluid of the pitcher plant. Only newly opened leaves actively attract and capture insects. As the leaves age, the insect victims slowly decompose and the leaf fluid pH is lowered. Since the leaves of a pitcher plant are of different ages, each leaf differs in its ability to capture insects and in the degree of decomposition of its captured insects. The relative abundance of the insect inhabitants of a leaf depends upon the leaf age, because each insect species consumes captured insect remains at different stages of decomposition. The buoyant larvae of B. fletcherl feed upon newly captured insects floating upon the surface. As the victims decompose, free-swimming W. smlthii larvae filter-feed upon the suspended particulate matter. Accumulated insect remains on the bottom of the leaf chamber provide food for M. knabl. Although all three species feed upon the remains of captured insects, they do so at different times and at different strata within the leaves.

Resource Overlap, Interspecific Interactions and the Distribution of the Flying Squirrels, Glaucomys volans and G. sabrinus

Abstract: The North American flying squirrels, Glaucomys volans (Linnaeus) and G. sabrinus (Shaw), provide an opportunity to analyze the role of various factors determining the ranges of two marginally sympatric species. A survey of the literature and observations of wild and captive Glaucomys suggest the following: (1) G. volans is almost always associated with hardwood trees; G. sabrinus is usually found in conifer forests but may occupy hardwood areas as well. (2) Especially in the North, G. volans appears to depend on tree hollows for nesting sites; G. sabrinus also nests in hollows but frequently uses outside nests. (3) Although omnivorous, volans is mainly a seed and nut eater over much of its range and depends on these resources during the winter. The northern part of its range coincides with the northern range limits of most mast species, especially the hickories (Carya) and oaks (Quercus). Glaucomys sabrinus, also relatively omnivorous, often subsists on lichens and fungi. Since lichens are abundant in its habitat and are eaten by few other animals, sabrinus has an exclusive energy

Life History Patterns of Ambystoma tigrinum in Montane Colorado

Abstract: A survey of approximately 60 ponds in the Gunnison Basin, Gunnison and Pitkin counties, Colorado, U.S.A., showed a cor- relation between the thermal ranges of the ponds and the life history pattern of Ambystoma tigrinum populations. Characterization of physical and biotic parameters allowed a ranking of ponds from warm to cool, verified by temperature data taken through two warm seasons (1974 and 1975). The life history pattern of the salamander populations was deter- mined on the basis of the number of size classes of salamanders observed in the pond. A model is proposed relating the thermal regimes of the pond and the observed life history pattern of the salamanders. Three life history patterns are defined for these populations: standard life his- tory, only one size class of larvae; neotenic life history, two size classes of larvae with metamorphosis occurring in the second warm season; and neotenic and paedogenic life histories, three or four size classes of larvae with metamorphosis occurring the the third or later warm season.

Primary productivity of emergent macrophytes in a Wisconsin freshwater marsh ecosystem

Abstract: In 1972 primary production of various emergent macrophytes was examined in Theresa Marsh, a shallow, semimanaged impoundment in southeastern Wisconsin. Dominant macrophytes included Typha latifolia, Scirpus fluviatilis, Carex lacustris, Phalaris arundinacea and a shrub, Salix interior. Seasonal patterns of production as well as total production varied greatly among species. With estimates for litter loss and belowground production, annual net primary production ranged from 1181 g/m/sup 2//year for Carex lacustrris to nearly 3200 g/m/sup 2//year for Typha latifolia. Peak standing crop values were generally among the highest reported. Average productivities during the growing season, however, were relatively low, ranging from 6.31 to 10.52 g/m/sup 2//day for aboveground standing crops. Primary production was also estimated for transient species that occurred on mud flats following a marsh drawdown. The high primary production within the marsh appears to be based on high nutrient levels as indicated by the marsh water and soil chemistry.

Characteristics of Mineral Licks and Behavior of Visiting White-Tailed Deer in Southern Indiana

Abstract: Characteristics of mineral licks and various facets of their use by whitetailed deer (Odocoileus virginianus) were examined in southern Indiana. Sodium (Na) levels were elevated in all licks, and Na was judged to be the element sought by deer. Use of licks by deer was maximum in early spring and moderated during the summer and early autumn; no winter use occurred. All sexes and ages except spotted fawns visited licks. Much aggressive interaction occurred at licks with no evidence of formation of a dominance hierarchy; only adult males were clearly dominant. It is concluded that the primary role of licks is the provision of Na during periods of Na deficiency. Requisite characteristics for any attractant proposed as an alternative to Na are discussed.

Response of Two Species of Peromyscus to Vegetational Succession on Land Strip-mined for Coal

Abstract: The influence^ of plant succession on the distribution of two species of Peromyscus was investigated on land strip-mined for coal 1-47 years earlier. Peromyscus maniculatus b air dit was most abundant early in succession when surface ground coverage was sparse and included little or no woody vegetation. As cover of shrubs and trees increased, P. leucopus noveboracensis became more numerous, and P. maniculatus dis- appeared from the community. Both species responded negatively to dense stands of grasses. Competition did not limit the distribution of Peromyscus on the areas studied.

The Life History of the Crayfish Orconectes kentuckiensis in Big Creek, Illinois

Abstract: Orconectes kentuckiensis was studied in Big Creek in southeastern Illinois from March 1972 to September 1975. It was most common in rocky pools where O. placidas was least common. Orconectes kentuckiensis feeds on plants and arthropods and is fed upon by at least two species of fishes. The species lives to a maximum of 2+ years and had survival rates of .280 and .029 for its 2nd and 3rd years. Form I males and females with maturing ovaries were present from July through April. Weight of maturing ovaries was strongly correlated (r==0.97) with female carapace length. Numbers of ovarian eggs ranged from 59-249 and numbers of abdominal eggs ranged from 49 248 ; both increased significantly with increase in carapace length. Mating was observed in October and November and oviposition occurred in March, April and May. Growth of lst-year crayfish occurred during a period of 4.5 months, of adult males during the spring and summer molts, and of adult females during the summer molt. Chela length and abdomen width were sexually dimorphic and exhibited allometric growth. One hybrid, O. kentuckiensis X O. placidus form I male was found.

Drosophila: Behavioral Cues for Oviposition

Abstract: A randomized block design was used to evaluate factors affecting oviposition by Drosophila melanogaster in a test system provid- ing a minimal set of behavioral cues. Age has no effect in mature females. Oviposition increases with adult density and with cyclic as opposed to constant illumination. Surface texture of the medium has a greater effect on increasing egg deposition in a cyclic light regime.

Reproductive Cycles in Two Species of Rattlesnakes

Abstract: The reproductive cycles of the Eastern massassauga (Sistrurus c. catenatus) and timber rattlesnake (Crotalus h. horridus) are described. The massassauga had 11.1 young per female, generally had their first young when 3 years old, and apparently reproduce annually. The timber rattlesnake had 7.7 young per female, generally had their first young when 4 years old, and reproduce biennially. Summer development of follicles is described in the biennial cycle and mating from August through May is suggested corresponding with rapidly developing follicles. A longer growing season appears to allow the massassauga to mature at an earlier age and reproduce annually; however, it is not clear if innate reproductive cycle differences may exist between the two genera of rattlesnakes.

A Latitudinal Gradient of Wood and Litter Production, and Its Implication Regarding Competition and Species Diversity in Trees

Abstract: Rates of wood and litter production in mesic forests along a latitudinal gradient are surveyed, and hypotheses concerning the eco- logical and evolutionary implications of emergent patterns are presented. Wood production is relatively constant along a latitudinal gradient, whereas total amount of light available during the growing season de- creases with increasing latitude. Therefore, efficiency of wood production is higher at temperate latitudes. We hypothesize that the higher wood production efficiencies at temperate latitudes came about as a result of selection for tree species with wood growth rates that are high during the growing season. Since rapid wood growth provides a competitive advan- tage in trees, we hypothesize that competition among trees is greater at higher latitudes. High efficiency of wood production apparently is a prerequisite for survival of forest trees at high latitudes. Only those tree taxa that had high wood production efficiency, or were able to evolve a high efficiency, survived when the primarily tropical or subtropical environment at higher latitudes turned much colder during the late Tertiary. This situation contributed to the present low diversity of trees at high latitudes relative to that at lower latitudes.

Observations on Reproduction and Phenology in Some Perennial Asters

Abstract: Populations of several perennial Aster species from dif- ferent habitats and a wide geographic range were cloned and compared under uniform environmental conditions in Urbana, Illinois. Differential responses to the changed environment were in part species-dependent, but mostly were a reflection of genetically fixed adaptation of populations to climate and light conditions in their native habitat. The following ob- servations are noteworthy: (1) Perennial asters are outbreeders. (2) Spontaneous seed production is variable and highest in weedy species, e.g., A. pilosus and A. simplex. (3) Several habit forms can be distin- guished, depending on the taxon: (a) a colonial form which reproduces vegetatively by means of stoloniferous rhizomes; (b) a cespitose form or caudiciform plants with short, often cormoid rhizomes, which give rise to distinct clumps; (c) an intermediate form, exemplified by taxa in the section Multiflori, which exhibits cormoid rhizome portions and cespitose clumps interconnected by horizontal strands; (d) caudiciform plants capa- ble of spreading by means of root sprouts, so far found only in A. pilosus. (4) The presence of geographic gradients was confirmed for Aster by a comparison of flowering dates recorded from the place of origin with those observed in the transplants. The phenology of flowering is under genetic control and determined by at least two independent adaptive stimuli which interact with climatic gradients. While the stimulus of flower initiation is primarily governed by photoperiod, the stimulus for bolting and formation of the inflorescence aopears to be determined largely by light intensity in interaction with temperature. (5) For most Aster species, the period from anthesis to maturation of fruit is approxi- mately 1 month. The achenes in some species require stratification but those of many species can be germinated immediately after harvest. In all species examined, seed germination can be forced at any time by rupturing the pericarp and the seed coat.

Aspects of the Larval Ecology of Five Plethodontid Salamanders of the Western Ozarks

Abstract: The larval ecology of five locally sympatric species of salamanders was investigated in NE Oklahoma. The data indicated a considerable degree of spatial segregation determined, at least in part, by species interactions. Similarities in prey composition and habitat use also suggested the possibility of competitive interaction. Temperature preference, effects of floods and effects of fish pr?dation were evaluated experimentally, and these data, in conjunction with field observation, lead to the conclusion that these factors were not primary causes of the spatial patterns observed in the field. Competition for optimum habitats was suggested as the primary cause and this is now being investigated by field manipulation of larval populations.

Activity and Ecological Distribution of the Slug, Arion subfuscus (Draparnaud) (Stylommatophora, Arionidae)

Abstract: Populations of the slug, Arion subfuscus, were studied in a goldenrodaster field and in wooded areas in central New York State. Absolute density was estimated by counting the slugs extracted with water from soil samples, and relative densities by counting the slugs attracted to metaldehyde bait or to wooden boards. Daily and seasonal activity patterns were dependent on temperature and moisture conditions. The annual life cycle was flexible and was dependent on the habitat; in the field slugs died by July, but in woods adjacent to the field, where the canopy moderated weather conditions, slugs survived beyond July. Slugs ate a wide variety of foods but fungi and decaying vegetation were eaten most frequently. Slug abundance was statistically correlated with the relative abundance of timothy grass, and it was suggested that timothy was favorable to slugs because of the shelter it provided. Arion subfuscus was not associated with any particular tree species but was found beneath all of the species examined, of both deciduous and coniferous trees. Although A. subfuscus is limited physiologically by extremes of temperature and moisture, its ecological requirements are flexible, enabling it to be a generalist species.

Feeding Ecology of a Population of Eastern Chipmunks (Tamias striatus) in Southeast Ohio

Abstract: Food resource fluctuation and composition of diet were continuously monitored for a population of eastern chipmunks (Tamias striatus) in SE Ohio from May through October 1975. Three food categories were used extensively by the population: plants, invertebrates, and fungi. Chipmunks selected subsets of the food available in each category. Plant material formed the bulk of spring and autumn diets. The relative proportion of invertebrate and fungal food in diets increased during summer. Adult males consumed significantly more plant and less invertebrate material than did other age-sex classes. Regression analysis revealed positive relationships between invertebrate and fungal availability and their percentages in the diet. Chipmunk activity was positively related to fungal consumption and inversely related to plant (reproductive structure) consumption. Explanations are offered for the trends observed. Discriminant analysis revealed a distinction between adult and juvenile feeding behavior based on invertebrate consumption, adults consuming smaller amounts of invertebrate food. In addition, adult feeding behavior was consistent while that of juveniles was interpreted as being adaptively flexible.

Competition and spacing in plant communities: differential mortality of white pine (Pinus strobus L.) in a New England woodlot.

Abstract: A relatively pure, uneven-aged stand of white pine (Pinus strobus L.) was studied to examine the relationship between differential mortality and the subsequent spatial pattern. Intraspecific competition in white pine occurs both within and between members of the canopy and understory. The effect of this competition is that almost all mortality in the stand is occurring in the understory pines. In addition, there is a pattern to the mortality of understory members competing with pines in the canopy. Depending upon the distances from a member of the canopy which understory pines establish, there is an upper limit to their size beyond which these individuals cannot survive. This pattern of mortality prevents entry of understory pines into the canopy and leads to the spatial pattern observed in the population, aggregated among members of the understory and random among members of the canopy. The patterns of differential mortality and spacing observed are interpreted with respect to Pielou's (1960) model. Finally, the failure to find a regular spatial pattern in this study and the relative rarity of such patterns are discussed.

Phenology, Distribution and Survival of Atriplex triangularis Willd. in an Ohio Salt Pan

Abstract: In an Athens Co., Ohio, salt pan, there were four vegetation zones: the Meadow, H or deum, Atriplex and Pan zones. These constituted a salinity gradient from the nonsaline Meadow to the highly saline Pan. The phenology, survival and distribution of the halophyte, Atriplex triangularis Willd., within this salt pan were investigated. The life cycle of A. triangularis spanned 9 months from February to October. The germination period extended from February to May. Flowers appeared in mid-July; seed development began in September. Senescence and death followed in late October. The population dynamics of A. triangularis were related to three main factors: soil temperature, soil moisture and soil salinity. Soil temperatures of 15 C appeared to trigger germination. High soil moisture values with consequent low soil salinity were prevalent during the winter-early spring germination period. Seedling establishment was particularly sensitive to salinity with severe mortality occurring in late spring and early summer when soil moisture values started to decline and salinity began to climb. The highest concentration of soil salts coincided with the flowering stage in July and August when soil moisture values dropped severely due to low rainfall and high evaporation. By the seed development and maturation stage in September, soil moisture levels had begun to rise due to heavy autumn rains and decreased evaporation which led to a decrease in total soil salts. The germination and survival of Atriplex triangularis were restricted in the main to the Atriplex zone. The relative absence of A. triangularis in the Meadow zone stemmed from the interference from the existing meadow vegetation. The rapid growth of Hordeum jubatum hindered the establishment of A. triangularis in the H or deum zone. High soil salinity within the Pan zone prevented the germination of A. triangularis.