Showing papers in "American Midland Naturalist in 1976"

Aquatic invertebrate abundance in relation to changing marsh conditions

Abstract: The relationship between invertebrate populations and vegetative cover was studied in several Iowa marshes during the peak of the avian nesting season. Shallow water with emergent and floating dead vegetation produced the most isopods, planorbid snails and physid snails. Physid snails had another abundance peak in areas where submerged plants were found below dense free-floating plants. Midges reached greatest abundance in more open habitats somewhat protected from the wind. Amphipods were the most numerous invertebrate taxa and were most abundant in dense beds of submerged vegetation. Cladocera and copepods were most common in quiet pools with little vegetation. Total invertebrate abundance increased as the emergent vegetation was replaced by submerged vegetation, but maximum numbers occurred where beds of submerged vegetation were interspersed with stands of emergent vegetation. It is suggested that nesting marsh birds are attracted to marshes that produce the most invertebrates.

Seasonal Changes in Weights of Marmots

Abstract: Seasonal changes in the body weights of yellow-bellied marmot (Marmota flaviventris) populations were studied for 8 years in western Colorado. Marmots may be classified by size into four age groups: juvenile, yearling, 2-year-old, and 3-year-old or older, each group with significantly different mean body weights. For each age group, the mean body weight of males was significantly larger than that of females. Mean body weights in June of yearlings and older were smaller, the later the onset of the growing season. All age groups made signifi- cant weight gains each year; there was no significant difference in growth rates among years. When the rates of weight gain of juveniles are corrected for time of appearance aboveground, the regression coefficients are virtually identical. The earlier young marmots are weaned, the more they weigh at hibernation and the more likely they are to survive hibernation. The percentage of young surviving their first winter of hibernation is significantly greater the earlier spring begins. Marmots at 3400 m elevation had growth -rates similar to those of mar- mots at 2900 m elevation. The adaptive strategy of marmots includes rapid growth rates, high tissue growth efficiencies and extension of the growing season by repro- ducing immediately following hibernation.

Phenological Pattern in the Shortgrass Prairie

Abstract: Data were collected for 1 year on 34 range plant species and for 2 years on six species to describe phenological timing in the shortgrass prairie of northeastern Colorado and also to determine whether there were any distinct groups of plants for which a single species could be used as a phenological indicator. Observations were made in four grazing treatments and two water amendment areas (one with 100 kg/ha mineral N ad'ded). Water amendments altered the phenology of some species, while grazing and nitrogen treatments had no measurable effects on phenology. Standard cooland warm-season classification of plants does not adequately describe the phenological dynamics of the shortgrass prairie. For example, Buchloe dactyloides, a warm-season grass, flowers with Agropyron smithii, a cool-season grass, rather than with Bouteloua gracilis, another warm-season grass. Four general categories of plants having different flowering capacities are recognized: blooming only once very early in the growing season; blooming twice with a summer dormancy period; blooming once during midsummer with blooming delayed during drought; and blooming only once late in the growing season. INTRODUCTION An understanding of phenological progression of plants is basic to understanding the functioning of a grassland ecosystem and is important in sound resource management (Costello, 1939; Lieth and Radford, 1971). Phenology is associated with plant growth rates (Taylor, 1972), nutrient transfer (Sosebee and Wiebe, 1973), thermal requirements (Nuttonson, 1955), plant-water relationships (Blaisdell, 1958) and perhaps even evolutionary change (Leopold, 1961). The objectives of this study were: (1) to describe the phenological progression of a broad spectrum of shortgrass prairie species; (2) to develop an approach for monitoring the phenological progress of the shortgrass prairie plant community by observing a few indicator species, and (3) to compare water treatment and annual weather variation effects as well as any observable differences in phenological state between grazing treatments or fertilization. These measurements, when combined with abiotic and other biotic measurements, will lead to a clearer understanding of the structure and function of the shortgrass prairie ecosystem. SiTE DESCRIPTION The Pawnee Site (intensive research site of the US/IBP Grassland Biome) ig located on the western edge of the USDA Central Plains Experimental Range, approximately 12 km N of Nunn, Colorado, at an elevation of 1652 m. Topography is gentle rolling plains. The major soil types are Ascalon, Vona, Renohill and Shingle, with Ascalon predominating on the sampling areas (Reuss, 1971). Annual precipitation varies from 254 to 381 mm, about 80% occurring from May to

Regeneration in Quercus lobata Savannas, Santa Lucia Mountains, California

Abstract: Geographic distribution and vegetational affinities of Quercus lobata communities in the Santa Lucia Mountains of central coastal California are discussed. In eight localities representing different physiographic types of oak savanna, size-class distributions and successional trends were studied. Few Q. lo-bata seedlings or sapling were found. Some higher-elevation savannas are being invaded by Pinus coulteri, P. ponderosa, Quercus chrysolepis and Q. wislizenii. Low fire frequency may be part of the cause of this conversion of deciduous oak savanna to pine and sclerophyll forest. Detailed observations on Q. lobata regeneration were made at one ungrazed locality. Despite heavy predation on acorns, Q. lobata seedlings do start in this area, but under present deerand rodent-browsing conditions seedlings do not become saplings.

Changes in Arthropod Abundance in a Highland Costa Rican Forest

Abstract: Arthropod populations in the understory of a Costa Rican, lower-montane rain forest were monitored periodically for 19 months by sweep sampling and Malaise trapping. Abundance fluctuated threefold during the study and was highest in the late dry season and early rainy season, April through June, and lowest during the cooler, windy months of November through January. High species diversity (H' and a) in Coleoptera coincided with peak abundance. Average body size in the whole fauna was largest in April, when arthropod numbers were high. Peaks in abundance of some predatory groups lagged behind peaks in other arthropod groups. The annual cycle appears to be composed of a series of short-lived, seasonal subfaunae. Results are discussed relative to plant productivity, climatic factors and findings from other locations. INTRODUCTION Recent studies in neotropical environments (Janzen and Schoener, 1968; Robinson and Robinson, 1970; Janzen, 1973a, 1973b) have shown that in areas with a marked dry season, arthropod populations are low in numbers of individuals and species during the dry period. This article reports on changes in arthropod populations in a middleelevation forest in Costa Rica over a 19-month period.

Distress Screams as a Measure of Kinship in Birds

Abstract: The piercing distress screams given by winter birds are hypothesized to be cries for help (usually in the form of mobbing from altruists) and to have been evolved by kin selection. The screams are apparently directed at the screamer's associates, not the predator, a point which supports our hypothesis of selection for altruistic behavior and weakens self-interest selection as a viable mechanism for their evolution. The screams are highly localizable, and attracted individuals are known both to mob predators and to experience risk in doing so; these facts argue that it is the attracted individuals which are altruistic, not the screamer. For two species, the proportion of individuals that screamed when mist-netted diminished as winter progressed; this suggests that kin selection and not selection favoring reciprocal altruism resulted in the evolution of such behavior. Our most powerful arguments that altruism, rather than self-interest selection, is the mode by which distress-screaming behavior was evolved are: (1) that permanent residents scream more than winter residents, and (2) that among winter residents, diurnal migrants scream more than nocturnal migrants. The very important implication of this work is that measuring the frequencies of such screams in samples of mist-netted birds provides an ordinal index of kinship (or at least, stability of interindividual associations).

Impact of moose browsing on boreal-type forests of Isle Royal National Park

Abstract: Measurable long-range effects of moose browsing were found in a boreal-type forest at Isle Royale National Park. Overall forest density decreased while average basal area per tree increased. Total basal area and reproduction density were unaffected. Balsam fir densities were drastically reduced, especially in younger age classes. For the most heavily used site, the oldest firs affected are linked to the time of moose arrival on Isle Royale. Mountain ash densities were also drastically reduced. White spruce, unpalatable to moose, increased in density, possibly due to reduced competition from fir. Birch and aspen densities were relatively unaffected. Their stems were mostly out of reach of moose when these animals first arrived. Reduction in fir and mountain ash densities accounts for the reduction in total tree density. Total cover in the shrub layer was unaffected by browsing, but averace stem height decreased. Taxus canadensis has almost disappeared on all browsed sites. Cover of low vascular plants and the ratio of windfalls to standing trees increased. INTRODUCTION The forests of Isle Royale National Park show several striking effects of moose (Alces alces andersoni) browsing. Many shrubs and tree saplings are truncated 1-1.5 m above the ,ground. Balsam fir (Abies balsamea) saplings appear scraggly and misshapen. Older firs exhibit a distinct browse line '2.5-3.5 m above the ground. Moose appear to be a maior ecological factor influencinz the successional development of the forest as well as the characteristics of the climax. The purpose of this study was to determine the extent of this influence. It is one phase of a comDrehensive research proiect aimed at investigating all maior aspects of the ecology of the upland boreal forest type in the park. It has been supnorted by the United States National Park Service and the Michigan Technological University. The effects of moose on a forest were studied by Berzerud and Manuel (1968) in the Noel Paul Drainage of Newfoundland where the forest type closely resembles that of Isle Royale. The emphasis in their study was on evaluating the effects on reproduction of tree sgecies and on determining the moose-carrying capacity of the area. Pimlott (1965) studied the effect of both moose and deer browsing upon major tree species in both Newfoundland and Anticosti Island. STUDY AREA Isle Royale National Park is an archipelago consisting of a large island about 72 km long and 14 km wide at its widest point and surrounded bv approximately 200 small islands. It lies in the western portion of Lake Superior 24 km SE of the Canadian shore and 72 km NW of Michigan's Keweenaw Peninsula. Uptilted layers of basaltic

Toxicity of Artemisia californica to Four Associated Herb Species

Abstract: Natural and artificial rain drip, soil and leaf volatiles from Artemisia californica are toxic to Hypochoeris glabra and Madia sativa but not nearly as toxic to Bromus rigidus and Festuca megalura. This supports the hypothesis, based on distributional patterns and animal exclosure experiments, that the former two species are allelopathically excluded from thickets of A. californica, but that the latter two are not. Volatile toxins are adsorbed by the soil during the dry season and released into the soil solution with the first rains. Toxins also come from litterfall and rain drip. Toxicity exists only at the very beginning of the wet season, after which the soil, leaves and rain drip become relatively innocuous.

A Fiel'd Study of Nesting Behavior of Male Bluegill Sunfish (Lepomis macrochirus Rafinesque)'

Abstract: The' nesting behavior of male bluegill sunfish (Lepomis macrochirus) in the field was described with particular emphasis on the frequency of selected agonistic and reproductive behaviors as a function of nest-site location. Nest construction, courtship and spawning were typical of the family Centrarchidae. Agonistic behavior was increased in crowded nesting situations. Spawning males were more aggressive than nonspawning males and often left the nest, which provided oppor- tunities for other males to enter the nest and engage the female. Simul- taneous polygamous spawning is a natural, although relatively rare, occurrence for bluegills.

Chemical Inputs by a Colony of Franklin's Gulls Nesting in Cattails

Abstract: Franklin's gulls nest at the Agassiz National Wildlife Refuge, northern Minnesota, after migrating from South America. Nutrient inputs by the gulls during 1971 were examined by comparison of water and sediment samples from two shallow pools. On pool was colonized by about 30,000 gulls nesting among cattails; the second pool contained cattails without a gull colony. Large increases occurred in nitrogen and phosphorus concentrations of water in the immediate vicinity of the gull colony; peak concentrations were concomitant with the peak of gull nest-building and feeding activities (mid-May and mid-July). About 36% of the annual phosphorus input to the pool with the gull colony is attributable to the gulls. However, there were no net changes in concentrations of nitrogen and phosphorus in water of either pool as a whole, i.e., nutrient concentrations in inflow and outlet waters of both pools remained relatively constant throughout the year due to nutrient absorption by the pool sediments. The gull colony had little effect on the concentrations of sodium, potassium, calcium and magnesium in water. Outlet waters of both pools had higher potassium concentrations than inputs, due to release of potassium by the sediments to water, or by nutrient uptake by cattails and subsequent leaching of both living and dead cattails. Most nutrients accumulated in the sediments, especially in the pool with the gull colony. The Rufuge acts as a "sink" for nutrients in runoff from surrounding ag,ricultural land.

Life History and Ecology of the Freshwater Caridean Shrimp, Palaemonetes paludosus (Gibbes)

Abstract: The life history and ecology of the freshwater caridean shrimp, Palaemonetes paludosus (Gibbes), was determined from monthly collections for 1 year in the Hillsborough River near Tampa, Florida. Numerical abundance increased from May (95.3/m2) to August (662.6/M2) and then decreased to 121.6/M2 by April of the following year. Biomass showed three distinct peaks, the largest occurring in November (49.2 g/m2). Females outnumbered males in all months except January and May. Ovigerous females ranging from 20-40 mm long occurred from early February to mid-October at water temperatures of 18-33 C; percentage of ovigerous females among mature females was highest (56%) in April. Fecundity ranged from 8-85 eggs and increased with length of the female according to the relationship: Log Y = 0.6228 + 0.0294X. Mean brood size and mean size of ovigerous females decreased from the beginning of breeding to June. Mean brood size was lowest in the last month of breeding. The incubation period in the laboratory was 12-14 days at 26-28 C, Growth to maturity (20 mm) took 2-3 months when water temperatures exceeded 26 C and 4-5 months when temperatures were lower. Postspawning mortality occurred from April to October. Longevity was confined to 1 year. Food consisted primarily of algae, vascular plants, detritus and aquatic insects, in decreasing order of importance. INTRODUCTION The grass shrimp, Palaemonetes paludosus (Gibbes), is common in fresh waters E of the Allegheny Mountains, from New Jersey to Florida. It also occurs in Mississippi, Louisiana, Texas and Oklahoma, probably introduced in the latter three states (Holthuis, 1952). In 1958 the species. (supplied by the Florida Game and Fresh Water Fish Commission) was introduced into the lower Colorado River by the California Department of Fish and Game and now is established in various locations (Hayden and Ringo, 1963; St. Amant and Hulquist, 1969; St. Amant and Day, 1972). Palaemonetes paludosus is predominantly a freshwater species but has been reported in brackish (Tabb and Manning, 1961; McGuire, 1961; Rouse, 1969) and salt waters (St. Amant and Hulquist, 1969). Dobkin and Manning (1964) observed survival at salinity of 300/oo (parts per 1000) in the laboratory. Although Dobkin (1963) described the larval development of Palaemonetes paludosus, there are no complete life history studies of the species. Numerous investigations have been published on P. kadiakensis Rathbun, the other epigean freshwater Palaemonetes in the United States [Meehean, 1936 (as "P. paludosa," see Holthuis, 1952; 1 Present address: Department of Biological Science, Florida State University, Tallahassee 32306.

Spider Size, Microhabitat Selection, and Use of Food

Abstract: The spider community inhabiting Mahonia aquifolium in an English woodland was examined to record size-dependent adaptations. All size classes of spiders were distributed nonrandomly on the types of leaflets, and in winter small spiders were located in a specific site beneath leaflets. With an increase in spider body length there were increases in percentage of spiders with webs, web size, and in the proportion of spiders that were feeding. Vertical sticky traps provided data on the abundance, location and sizes of potential prey. Spider feeding was proportional to the density of potential prey. Orb webs differed from other webs in the study area due to their shorter duration and increasing catch with increasing size. The variation in the orientation of orb webs from horizontal for small webs to vertical for larger webs probably explains the increased prey-catching success of larger orb webs.

Reproductive behavior in an overwintering aggregation of Monarch butterflies

Abstract: Mating is an important part of the daily activities of monarch butterflies in late winter in southern California. Mating activity increased steadily from late January 1972 until late February 1972. During the final week of February this activity decreased, coincident with the dispersal of butterflies from their clustering areas. Prior to mating, males pursue, capture and overcome resistance by female butterflies. In flights of mated pairs only males flap their wings. In overwintering areas male monarchs apparently do not signal females as reported for other danaid butterflies. Males frequently pursue and attempt copulation with other males; but since they more frequently pursue and canture females, they are evidently able to discriminate between the sexes. Females disapTear from the clustering sites earlier than males and shortly thereafter deposit eggs on local milkweed.

Surface Film Locomotion by the Water Strider, Gerris remigis Say

Abstract: The study resolves conflicting observations of previous research and adds to our knowledge of surface film locomotion by the Gerridae. Water striders perform two kinds of movements "gliding" and "leaping." The power thrust for these movements is provided by mesothoracic legs only, with the proand metathoracic pairs giving stability to the body. In gliding motion, metathoracic legs do not move. In leaping motion they do move, but frictional drag and limb inertia are more likely responsible for their relative backward movement than a rowing action. Backstroke recovery of the mesothoracic legs in both motions is by lifting and bringing them forward over the head. Turning is done by unequal power strokes of mesothoracic legs, while the metathoracic leg on the inside of the turn serves a pivotal function.

Sexual Activity of the Gypsy Moth" 2

Abstract: Female moths that had begun to deposit unfertilized eggs (spewing females) did attract males and were mated. However, only females that had spewed fewer than 10 eggs before matingf were likely to deposit fertile eggs after mating. Males in a natural infestation did not discriminate between mated, virgin, spewing and nonspewing females. Both sexes of the gypsy moth were capable of mating several times in 24 hr. About 1/3 of the males in a dense population were mating with pre- viously mated females. In the microencapsulated,. disparlure-treated plots, only 1- to 4-day-old females were mated. In untreated plots, 1- to 8-day- old females were mated. Furthernore, fewer females tethered in the litter in the treated plots were mated than those females tethered in the litter in control plots. The disparlure treatment reduced the incidence of mating. In treated plots, more females tethered on the tree at 2 m were mated than females tethered in the litter. Videotaped activity of males in a dense population revealed that males orient to vertical silhou- ettes initially, and not to specific pheromone sources.

Coniferous Forest Habitat Types of the Wind River Mountains, Wyoming'

Abstract: The potential vegetation was studied in the Wind River Mountains of northwestern Wyoming. Five coniferous forest habitat types were recognized, and quantitative data for structure of tree popula- tions, cover and constancy of major undergrowth species, soil chemistry and topographic position given for 69 stands of relatively undisturbed vegetation. Although relatively stable vegetation was the principal basis for recognition of the forest habitat types, other site characteristics were considered. The relationships of the habitat types in the Wind River Mountains with other coniferous forests in the Rocky Mountains are discussed.