Showing papers in "Ecological Monographs in 1977"

The Establishment and Development of a Marine Epifaunal Community

Abstract: Because of the nature of their substratum, the sessile invertebrate species of the marine epifaunal community living on rocks occur in discrete patterns of distribution. The rocks are finite patches or habitat islands with a limited space for colonization and growth. Such a system is ideal for studying the parameters affecting the distribution of species within a community. Also, because of the small size and immobility of the adults, the system is also ideal for studying the pattern of change in species composition and diversity within a community. This study used multiple series of manipulated experimental plates, which both duplicated natural rock surfaces and could be compared with samples of the rocks, to investigate the developmental and distributional processes of this community. Five major factors were found to be important to both the development of the community and its distribution on the rocks: (1) the selectivity of the metamorphosing larvae as to site of attachment; (2) the seasonal fluctuat...

Stabilization of the Rate of Nitrogen Accumulation by Larvae of the Cabbage Butterfly on Wild and Cultivated Food Plants

Abstract: Larvae of Pieris rapae (Lepidoptera: Pieridae) were reared on several crucifer species and varieties which differed in their nitrogen content, either naturally or because they had been fertilized with NH4NO3. Growth rates, food consumption rates, and efficiencies of food utilization were determined for fifth instar larvae on all plants, using standard methods. Larvae on low-nitrogen plants consumed food faster, utilized it less efficiently, and utilized N more efficiently than larvae on high-nitrogen plants. As a result, growth rates and rates of accumulation of N into larval biomass were as high on plants of 1.5% (dry wt) N as on plants of 4.8% (dry wt) N. There was no correlation between larval growth rate and reported patterns of glucosinolate content in the food plants. We attribute low N accumulation rates and growth rates on Lepidium virginicum, Lunaria annua, and Thlaspi arvense to the presence in these plants of unique secondary compounds or atypical glucosinolate breakdown products. Larvae fed on Dentaria diphylla and on the most highly fertilized collards (6.1%% dry wt N) accumulated N and grew at unusualy high rates. This may be because N in these plants was more digestible than in the other food plants. We suggest that larvae of P. rapae adjust their feeding rates to maximize the rate at which they can accumulate N, and thus the rate at which they can grow, on any given food plant. There is a limit to the rate at which N can be accumulated, because N is utilized less efficiently as it is consumed faster. We conclude that the growth of P. rapae larvae is limited by the availability of N in their food plants, that N budgets for such larvae are of greater ecological significance than energy budgets, and that, in this case at least, natural selection favors the rate (power output) rather than the efficiency of a biological process.

Development and Stability of the Fouling Community at Beaufort, North Carolina

Abstract: Community development was followed for 2 1/2 to 3 1/2 years on unglazed ceramic tile plates (232 cm2), suspended horizontally beneath the Duke University Marine Laboratory dock, in Beaufort, North Carolina. Series of 3 or 4 plates were submerged at approximately the 1st of each month from May—November 1971 and from April—November 1972. Percentage cover for each species that settled and grew on the lower surface was estimated at 6— to 8—week intervals, using 75 points randomly positioned over the plate area. Samples were nondestructive; plates were resubmerged after each census. Larval recruitment was estimated at 1— to 3—week intervals on newly submerged plates. Temperature and salinity were also measured. Initial community development was relatively unpredictable. Larval recruitment patterns varied markedly from year to year and as a result, different patterns of initial community development were observed both within and between years. Instead of preparing the way for subsequent arrivals, most resident adults strongly inhibited the recruitment and growth of other species. Species varied in their ability to resist subsequent invasion as adults and in their ability to invade occupied substrate as larvae. After an unpredictable initial developmental phase, subsequent changes in species composition depended in part on the degree to which larvae were able to invade existing adult assemblages. This in turn depended on the identity of the resident adults and the identity of the invading larvae. As a result, the direction and rate of community development, dependent on the order of initial invasion and subsequent recruitment, were difficult to predict although an equilibrium number of 8—10 species/plate was often observed. Adult residence time was generally <1 year and the mortality and/or disappearance of these adults produced 20—60% free space on an approximately annual basis. This free space was usually occupied by recruits of a different species than the original occupant. The combined addition of species through larval recruitment and subtraction of species as a result of adult mortality produced dramatic changes in community structure each year. There is no reason to believe these changes will ever cease. We conclude that succession in the classical sense (Odum 1969) does not occur in this system because initial development was variable, residents impeded subsequent development instead of enhancing it, and there was no stable climax. There is good reason to believe similar processes occur in other temperate and subtropical fouling communities. We believe these communities are fundamentally different from terrestrial plant communities, where succession may occur, for 3 reasons: (1) the organisms do not alter the substrate they occupy, i.e., “prepare” it for later arrivals, (2) there is no possibility of “storing” dormant “seeds” of successional species. Colonization of free space is generally by animals which have a short—lived, even nonfeeding larvae, (3) most adults are extremely short—lived. An emerging paradigm of marine benthic community organization postulates the existence of competitive hierarchies in which 1 or a few species win in the absence of disturbances. The fouling community appears to lack such dominants.

Preferential Feeding: An Optimization Strategy in Sea Urchins

Abstract: Strongylocentrotus drobachiensis and S. franciscanus exhibited strong algal preferences in laboratory studies. A generalized ranking of algae from most to least preferred for both sea urchins includes: Nereocystis luetkeana, Costaria costata, Laminaria saccharina, L. groenlandica, Monostroma fuscum, Opuntiella californica, Agarum fimbriatum and A. cribrosum. Similar but weaker preferences were exhibited by S. purpuratus. Preference experiments showed that substance(s) readily sloughed from the fronds of Nereocystis attract urchins whereas substances from A. fimbriatum repel or are not detected by urchins. In the field urchins in contact with or on the fronds of Agarum spp. revealed a low proportion of feeding individuals except during winter. Food preferences were inversely correlated with the caloric content of algae. Although preferences generally were weakly correlated with caloric intake, this relationship is an artifact of the high feeding rates on preferred algae. Absorption efficiencies for the thr...

Coadaptations of the Clark's nutcracker and the pinon pine for efficient seed harvest and dispersal.

Abstract: Clark's Nutcracker (Nucifraga columbiana) is one of four species of corvids that commences harvesting, transporting, and caching the seeds of pinon pine (Pinus edulis) in mid—August. Caching continues until inclement weather intervenes or the seed crop is depleted. Nutcrackers are efficient at collecting seeds from the trees because the birds discriminate edible and aborted seeds, select cones with higher than average number of good seeds and appear to concentrate on those trees that produce cones with large numbers of good seeds. The use of a sublingual pouch allows the nutcracker to carry up to 95 pinon pine seeds per trip (x = 55). A pouch full of seeds may be carried as far as 22 km from the collecting area (the pinon—juniper woodland, elevation ~ 1800 m) to communal caching areas where the seeds are buried in clumps in subterranean caches at a depth of 2 to 3 cm. These caching areas are on steep, south—facing slopes that are usually free of snow by late winter. Although solitary nesters, the birds, during the nonbreeding season, often form flocks when harvesting seeds. A flock of 150 nutcrackers cached between 3.3—5.0 X 106 pinon pine seeds in the autumn of a good cone crop. Each bird caches between 2.2 and 3.3 X its needed energetic requirements for the insect—free portion of the year. Some of the unrecovered seeds germinated and grew. The pinon pine reaches its highest density in relatively dry areas below the elevational range of other members of the genus Pinus, but ranges up to 3,100 m into the mixed coniferous forest. This pine has developed a number of traits that enhance its efficiency to be located and dispersed by the birds. The seeds are unusually large, of high energy value, and have relatively thin seed coats. The large size improves the germination potential of the seed but also attracts predators and dispersal agents. The seed coat color is markedly different for edible and aborted seeds, thus labeling them for visually oriented seed harvesters. Most pinon pine cones are oriented outward and upward which increases illumination of the seeds and tends to hold them in the cone. The pinon pine displays the seeds in its cones more readily than wind—dispersed pines by opening the seed—bearing cone scales to a uniform angle. Pinon pine seeds are retained for a long period of time in the cone because they are held in deep depressions on the cone scales by small flanges. This constellation of features indicated an evolutionary strategy on the part of the pinon pine to exploit and encourage members of the seed—caching guild to disperse the seeds. Deposition sites are presumably more favorable for germination than those obtained by simply broadcasting the seeds over a wide area. Individual seedlings potentially experience immediate intraspecific competition because the seeds are cached in clumps. Only one seedling, presumably the strongest, fastest—growing individual, survives. The benefits of this system to the nutcracker are that the bird has a supply of energy for the most unproductive months of the year. The bird also breeds in late winter or early spring, using the stored seeds for reproductive energy.

Old‐Growth Pseudotsuga menziesii Communities of a Western Oregon Watershed: Biomass Distribution and Production Budgets

Abstract: Living biomass, organic matter distribution, and organic matter production budgets were determined for plant communities of a small watershed dominated by 450—yr—old Pseudotsuga menziesii (Mirb.) Franco forests. Dominant trees in the communities were large, up to 175 cm diam and 80 m tall. Aboveground tree biomass of the various communities ranged from 491.8—975.8 tonnes/hectare, total aboveground living biomass ranged from 500.4—982.5 t/ha, total leaf biomass ranged from 10.4—16.3 t/ha and total organic matter accumulations ranged from 1,008.3—1,513.7 t/ha. Total tree biomass in the various communities was more related to past mortality than habitat differences. Biomass of standing dead trees and fallen logs was generally inversely related to aboveground tree biomass. Amounts of woody detritus were large, ranging from 59.0—650.6 t/ha or 4.3%—43.0% of total community organic accumulation. Aboveground tree biomass increment was negative in all communities, ranging from —2.9 to —6.2 t/ha. Positive increment...

Comparative Ecology of Galapagos Ground Finches (Geospiza Gould): Evaluation of the Importance of Floristic Diversity and Interspecific Competition

Abstract: Distribution, abundance, diet, and beak morphology of the six Geospiza finch species were studied at eight sites on seven Galapagos islands. The resulting information was used to test the theories of Lack and Bowman that interspecific competition (Lack) and floristic and food differences among islands (Bowman) determine the ecological and morphological characteristics of the finches. Both factors were found to be important in different aspects of finch ecology. Most of the 21 populations studied spent more time foraging for seeds and fruits than for insects. Most populations had generalized diets and nine out of 18 pairs of sympatric populations had diets overlapping by 50% or more. Diet breadth was positively correlated with variety of available foods (classified by an index comprising measures of size and hardness), but was not correlated with abundance or biomass of sympatric populations of finches (potential competitors). Competitive release, in the form of large population biomass on islands with few congeners, was not found. Nor was population biomass related to variety of available food. Overlap in diet between two species was greatest when the species were most similar in abundance and body size. Interspecific competition is indicated by the distribution and morphology of the finches. The absence of four combinations of species cannot be attributed to change: (1) G. conirostris and G. fortis, (2) G. conirostris and G. scandens, (3) G. difficilis and G. fuliginosa, and (4) G. scandens and G. difficilis. These absences cannot be attributed to the absence of suitable foods. and sites with similar floras and suites of food types do not necessarily have similar ground finch faunas. The ecological and morphological similarity of members of each of the four pairs suggests an inability to coexist for competitive reasons. In contrast, where only two species occur together on an island they tend to differ markedly in size (beak and body) and diet. Species with large beaks can eat larger and harder seeds and fruits than species with small beaks, and as a consequence they tend to have more diverse diets. Species with large beaks also eat medium—sized seeds and fruits quicker than species with small beaks. Species with small beaks may be able to deal with small soft seeds more efficiently than species with large beaks, but the data are not clear on this point. In addition, small species with small beaks have a metabolic advantage over large species with large beaks. Variety of available foods influences the large species more than the small species: the two largest species, G. magnirostris and G. conirostris, occur only on sites where plants producing large and hard seeds and fruits are plentiful. Food variety apparently does not influence the degree of diet overlap. The number of plant species on an island statistically determines the number of land—bird species in general, and Geospiza species in particular, which occur on that island. The influence is probably mediated through food supply, since 53% of the variation in Geospiza species diversity among the eight sites was accounted for in a multiple linear regression analysis by diversity of available seeds and fruits. We conclude that food supply and interspecific competition have jointly determined the ecological course of the radiation of Darwin's finches and the resulting pattern of species diversity. Interisland variation in vegetation favored the initial steps of differentiation. Competitive interactions among species influenced later stages by determining which ecological types could coexist on an island with a given array of foods.

Organization of Contiguous Communities of Amphibians and Reptiles in Thailand

Abstract: In adjacent areas of broadleaf evergreen forest, deciduous dipterocarp forest, and agricultural land in northeastern Thailand, >4,000 individuals of 105 species of reptiles and amphibians were systematically collected. The position of capture of each individual was recorded in terms of a complex microhabitat code. The 3 environments differ substantially in pattern of human disturbance, in vegetation structure, and in range and predictability of temperature and total evaporation, the evergreen forest having the most buffered climate near the ground. Of the 3 environments studied, the evergreen forest has the most diverse and distinct herpetofauna, and the largest percentage of autochthonous species. The evergreen forest community has more southern or tropical affinities, while the deciduous forest community has more northern affinities. Analysis of the use of microhabitat categories by coexisting species reveals significant dif- ferences, even among the most similar sets of species. Differences in species richness among the three communities are not explained by differences in microhabitat diversity, mean niche breadth, or mean niche overlap. However, an ith nearest neighbor analysis of the dispersion of niche centers in resource space reveals closer packing and larger and more distinct guilds in the evergreen forest: the environment richest in species and the most predictable in climate. Both a graphical treatment and an analysis of sets of species grouped a priori according to their general natural history confirm the existence of larger and significantly tighter guilds in the evergreen forest. It is suggested that unpredictable environments tend to prevent the formation of distinct guilds, while the greater species richness of more predictable environments may be a function of guild formation.

Population Persistence and Density Dependence

Abstract: This paper reformulates the notion of density dependence and shows how this notion plays an important role in constructing appropriate models for data analysis. The regulation and persistence of population processes are interpreted as a close resemblance to the behavior of a series of random variables in which the second moments are bounded. On this basis the formal criteria of persistence are deduced. General structural models of population processes are set up and translated into discrete single—variable difference equations, ranging from the simplest linear first—order process to more complex nonlinear second—order processes. The discussion includes the derivation of general conditions for the second—order limit cycles, a reanalysis of the Canadian lynx 10—yr cycle, and models for population outbreaks. Based on the results of the preceding study of models, the notion of density dependence is reformulated. First, the meaning of the word 'dependence' is discussed. In the context of 'density dependence,' the word has two meanings; the causal dependence of a factor on density, and the statistical dependence. Statistical dependence is defined as a converse of statistical independence, the latter being a process in which the rate of change in density has zero correlation with density; this is a very special class of processes and is unlikely to occur in natural population processes. Therefore, the test of density dependence against the null hypothesis of statistical independence will not provide much insight. It is also argued that a deduction from the persistence criteria shows that a negative correlation between density and its rate of change is a necessary outcome of regulation and hence that the notion of 'density—dependent regulation' in statistical dependence is an uninspiring tautology. As opposed to statistical density independence, which necessarily generates an unbounded population process, causal density independence may satisfy the persistence conditions and hence may regulate populations. However, such a causally 'density—independent regulation' tends to be 'fragile' against perturbations by random exogenous factors. It is a particular class of causally density—dependent processes that can ensure regulation more durable against such perturbations. The inference of generating mechanism from observation is discussed. Although regression analysis is an essential method of inference, simple regression analysis will not work unless the observed processes are known to be a simple Markov chain. Statistical inference of generating mechanisms in observed systems depends largely on the choice of appropriate models, and it is in the construction of such models that the notion of causal density dependence plays an important role.

The Regulation of Element Concentrations in Mountain Streams in the Northeastern United States

Abstract: Concentrations of elements in streamwater were monitored in 57 watersheds located along elevational and successional gradients in the White Mountains of New Hampshire, USA. Concentrations of C1— and SO4– decreased with increasing elevation as a result of differences in relative evapotranspiration along the elevation gradient. Concentration of Na+, Ca++, and Mg++ also decreased with increasing elevation, but with a steeper slope. Rock weathering/unit of water flux as well as relative evapotranspiration controls concentrations of these cations. Potassium and NO3— concentrations were highly variable, both seasonally within a stream and among streams. Differences among watersheds in terms of successional status are important in controlling NO3— and K+ concentrations. Streams draining old—aged forested ecosystems had higher concentrations of NO3—, K+, and other plant nutrients than did streams draining intermediate—aged successional ecosystems at the same elevation. Nine spruce—fir watersheds which have no record of logging or other extensive human disturbance had streamwater NO3— concentrations averaging 53 microequivalents/litre, while five other spruce—fir watersheds which had been logged 30 yr previously had streamwater NO3— concentrations averaging 8 meq/1. The major factors controlling streamwater concentrations of elements in these watersheds are factors related to supply (precipitation chemistry, relative evapotranspiration, rock weathering) and to plant accumulation of nutrients. Rapidly—growing successional ecosystems can accumulate a large fraction of inputs of nutrient elements, particularly during the growing season. Steady state ecosystems, those with no net biomass accumulation, have nutrient outputs equal to nutrient inputs. The increased losses of nutrient elements from clearcut watersheds in New Hampshire can be explained in these terms. Clearcut or otherwise disturbed ecosystems may have mineralization in excess of plant uptake, leading to element outputs in excess of inputs. Field experiments demonstrated that the prevention of plant uptake by root trenching led to soil NO3— concentrations comparable to those observed in streamwater in the clearcut watershed at Hubbard Brook Experimental Forest.

Mechanism of Invasion and Dominance of Coastal Grassland by Mesembryanthemum crystallinum

Abstract: The invasion of Mesembryanthemum crystallinum into coastal grassland was observed at Surf on the central coast of California, USA. The species became established in areas unoccupied or sparsely occupied by other plants, and then grew into surrounding areas. The following season, few grassland seedlings established beneath dried Mesembryanthemum as compared to adjacent grassland. The reduction in numbers of grassland seedlings did not appear to be the result of limiting levels of moisture, light or macronutrients which were found in lower levels in the grassland, nor to be due to grazing by small mammals, since the pattern persisted in the absence of grazing. The differential pattern of seedling establishment was correlated with high levels of salt found in the soil beneath dried Mesembryanthemum. Mesembryanthemum crystallinum is an annual plant which accumulates salt throughout its lifespan. After the plant dies, this salt is released with leaching by fog and rain. The salt produces a detrimental osmotic environment preventing growth of nontolerant species. The salt does not appear to have a direct toxic influence on grassland species. Osmotic interference resulting from accumulation and release of salt appears to be the means by which Mesembryanthemum crystallinum dominates areas previously occupied by grassland.

The Distribution of Solar Radiation within a Deciduous Forest

Abstract: Solar radiation was measured within and above an east Tennessee deciduous forest over a 2-yr period. Diurnal patterns of within-forest radiation follow the temporal variation in incident radiation but become more irregular with depth in the forest because of the highly variable penetration of beam radiation in space and in time. Seasonally, radiation in the forest increases substantially from winter to its annual maximum in early spring as solar elevations increase. Although solar elevations continue to rise each day until the summer solstice, amounts of total radiation and its beam component drop sharply in the forest with the advent of leaf expansion. Diffuse radiation in the forest continues to increase slowly follow- ing the onset of leaf expansion but reverses as the forest approaches a fully leafed state. Fol- lowing the summer solstice, forest structure remains essentially static until abscission while solar elevations decrease. In summer and early autumn, total radiation and both its beam and diffuse components decrease slowly in the forest to their annual minimum in autumn. With leaf abscission and subsequent fall, radiation increases slightly in the forest but soon declines again as solar elevations approach their annual minimum of the winter solstice.

The life of the smooth newt (triturus vulgaris) after metamorphosis

Abstract: After metamorphosis, smooth or common newts (Triturus vulgaris vulgaris (Linn)) dis- perse on land, where they live as juveniles before returning to the water as breeding adults. The population age-structure was obtained by dissecting the standard length frequency distribution, a procedure which is justified in the text. Juveniles have an uncomplicated age-structure, the number of individuals in successively later age-classes being reduced by mortality and by recruitment to the adult population. Among adult newts, the most frequent age-class is nearly central, indicating the existence of extensive variation in the age at maturity. Growth continues throughout life, the rate of growth decreasing with age. The annual survival rate of adult newts as estimated by a census method, and from the age-structure, was found to be =50%, being rather greater in Y Y than in d d. Less reliable data indicate the annual survival rate of juveniles was -80%. Maturity is attained between the ages of 3 and 7 yr, most individuals reproducing for the first time at 6 or 7 yr of age. The number of eggs laid increases with age from - 100 at age 3 to -400 at age 12; there is also an effect of Y age on oocyte size, which may influence subsequent larval survival. Smooth newts breed annually. Reproduction diverts surplus energy from somatic growth, and thereby decreases potential future fecundity in animals whose fecundity is proportional to body size. Individuals maturing at different ages, therefore, have different schedules of fecundity, which were estimated through the use of microbomb calorimetry. Population size was found to be lognormally distributed, with a mean of -70. The sex ratio of juvenile newts was near equality, but a majority of Y Y comprised most adult populations. This imbal- ance is due to greater mortality of adult d d, which results in an age-specific trend in the sex ratio. There are 2 breeding migrations: 1 in autumn and I in spring. It is likely that newts migrate during autumn when about to reproduce for the first time, and thereafter migrate during spring. Terrestrial newts appear to move little; there is some evidence that colonization of newly dug ponds is achieved by the infrequent emigration of juveniles. During its life, a smooth newt occupies a succession of ecological niches. Moreover, different individuals may occupy different niches, or may occupy the same niches for different periods of time. It is speculated that in large newt populations the complex life history is able to trap genetic variation and to dampen fluctuations in population size. However, it is suggested that these group attributes have arisen largely as the result of selection between individuals. Breeding only once (rather than repeatedly) will reduce fitness because the additional fecundity necessary to balance the loss of later reproduction cannot be attained. Early maturity appears to be favored in d d, and late maturity in Y Y; these opposed selection pressures may contribute to the observed age variation at maturity. Finally, the sex ratio does not vary with population density, and is therefore thought to be controlled by natural selection.

An Analysis of the Dynamics of a Weddell Seal Population

Abstract: A breeding population of the Weddell seal (Leptonychotes weddelli) was studied annually during the 2 1/2—mo pupping and breeding season in McMurdo Sound, Antarctica, from 1969 through 1974. Components of the population were estimated by direct counts of adult ♂ ♂ with pups, by capture—recapture studies of nonparous ♀ ♀ and adult ♂ ♂, and by aerial counting. Total population size was estimated as being on the order of 2,500—3,000 seals. The Seber—Jolly method was adapted to circumstances of the present study. Reproductive rates (measured in terms of successful pupping) were ~ 0.5 pups/♀ for the entire breeding colony, and ~ 0.7 pups/♀ for a subset of tagged ♀ ♀ observed for 4 yr in sequence. Age—specific reproductive data were also obtained, and it appears that full reproductive activity of ♀ ♀ is achieved at ~ age 7. The annual survival rate for adult ♀ ♀ is in the range of 0.80 to 0.85, as determined (by several methods) from tagging data. Survival rates for adult ♂ ♂ are lower (perhaps 0.50), but are no...

Ecological relationships between mule deer and white-tailed deer in southeastern arizona

Abstract: Niche relationships between the desert mule deer (Odocoileus hemionus crooki) and Coues white-tailed deer (Odocoileus virginianus couesi) were studied in the San Cayetano and Dos Cabezas mountains in southeastern Arizona from September 1969 to March 1972. Walk transects were established on the study areas on which deer were observed. Altitude, slope exposure, and habitat selection were used to describe distributional patterns of the two species. Food habits were studied by analyzing fecal samples microscopically for epidermal fragments of important forage plants. Behav- ioral interaction between mule deer and white-tailed deer, browse utilization on Cercocarpos brevi- florus, and recruitment were also investigated. Spatial distributions according to altitude and slope exposure indicated that a "buffer" zone existed between populations of mule deer and white-tailed deer in the San Cayetano Mountains. Mule deer were associated with fewer vegetational types than white-tailed deer on this study area; Prosopis juliflora and Fouquieria splendens were indicative of mule deer habitat. White-tailed deer utilized a greater diversity of vegetational types in the San Cayetanos and did not appear to be associated with any particular plant species, although Quercus oblongifolia, Dasylirion wheeleri, and Eysenhardtia polystachya were important. The most important forage plants for white-tailed deer in the San Cayetano Mountains were E. polystachya, Eriogonum wrightii, Krameria parvifolia, and Fendlera rupicola. Similarly, the primary food items of mule deer were E. polystachya, Calliandra eriophylla, and K. parvifolia. There was much overlap in food preferences of mule deer and white-tailed deer (55% to 67% seasonally) particularly on E. polystachya and K. parvifolia. Populations of mule deer and white-tailed deer were sympatric in the Dos Cabezas Mountains; the coefficients of association were highly positive. There was also a great similarity in habitat selection between the two species. Both species were associated with those habitat types dominated by Quercus emoryi, Juniperus deppeana, C. breviflorus, Quercus gambelil, Nolina microcarpa, Symphoricarpos ereophilus, and/or Bouteloua spp. White-tailed deer displayed a greater preference for the Quercus- Symphoricarpos and Quercus-Cercocarpus habitat types than mule deer, whereas Juniperus- Cercocarpus habitats were preferred more by mule deer. Food habits of mule deer and white-tailed deer were very similar; all plant species important to white-tailed deer were also important to mule deer. The most frequent forage plants, in order of importance, were C. breviflorus, E. wrightii, J. deppeana, and Q. gambelii. Recruitment to the population was higher for mule deer than for white- tailed deer. Utilization of the annual leader growth on the key browse plant (C. breviflorus) was extremely high. Mule deer were dominant over white-tailed deer in all behavioral interactions observed during the study. In half of these instances, mule deer displayed aggressive threat in asserting their dominance; the rest were of a passive nature. The low coefficients of distributional overlap and high indices of overlap in food habits for the San Cayetano Mountains lead us to conclude that mule deer and white-tailed deer competitively exclude each other. The high overlap in spatial distributions, habitat selection, and food habits coupled with the high utilization of the key forage plant (C. breviflorus) in the Dos Cabezas Mountains during the winter months lead to the conclusion that direct competition between the two species probably was occurring during that time. This direct competition can be explained on the basis that it is a temporary phenomenon. It is hypothesized that the factors that have brought mule deer and white-tailed deer into direct competition in this area have been vegetational changes, livestock overgrazing and/or range fire suppression.

The Modern and Late Quaternary Vegetation of the Campbell-Dolomite Uplands, near Inuvik, N.W.T., Canada

Abstract: The Campbell—Dolomite uplands comprise a small area (140 km2) of outcropping, faulted dolomite, limestone, and shale east of the Mackenzie River Delta, ~ 40 km south of the northern limit of trees. The major landforms are bedrock ridges and plateaux, steep colluvium, stable slopes, shorelines, and depressions. A principal component analysis of vegetation—cover data from 150 stands suggest that much of the variation within the heterogeneous vegetation is correlated with these broad habitat categories. Stable surfaces bear an open spruce woodland with alder, tree and dwarf birch, and a varied lichen—heath—Dryas ground vegetation. A glacially modified karstic (solution) depression contains a small (8 ha), relatively deep (22 m), apparently meromictic lake, which yielded a 12,000—yr core of sediment. A conventional percentage diagram, an influx diagram, and numerical analysis (principal components) suggest a sequence of pollen assemblage zones as follows: (1) Salix—Gramineae—Artemisia: 13,000 to 11,300 radiocarbon yr ago, (2) Betula (shrub)—Salix—Gramineae—Artemisia: 11,300 to 10,300, (3) Betula—Populus: 10,300 to 9,700, (4) Betula—Populus—Juniperus: 9,700 to 8,900, (5) Picea—Betula (tree and shrub)—Juniperus: 8,900 to 6,500, and (6) Picea—Betula—Alnus: 6,500 to present. Both percentage data and numerical analyses show that none of the pollen assemblage zones 1 to 5 has a modern analogue. With 1 exception, these patterns of change in pollen spectra can be interpreted parsimoniously without reference to regional environmental change. They suggest an initial phase of migration of willow and herbs from adjacent unglaciated Megaberingia (North Yukon and Alaska), followed rapidly by dwarf birch and later poplar. Megaberingian floristic elements (e.g., Plantago canescens, Selaginella sibirica) reached the area during this early phase of migration. Subsequently arriving from the south along the Mackenzie valley were juniper, ericads, spruce, and finally alder, which intensified competition and restricted the early Megaberingian herb types to open, unstable habitats where they persist today. Slow soil development (humus accumulation, rising permafrost table) probably favoured the spread of the palynologically 'silent' elements–lichens, ericads, and Dryas (the dominants of the modern ground vegetation). Changes in the influx values of Picea suggest a climatically induced increase in tree density and/or pollen production during the period 9,000—7,000 BP (Zone 5).

Alpine and High Subalpine Plant Communities of the North Cascades Range, Washington and British Columbia

Abstract: Community types were described from 209 stands in the alpine zone of the North Cascades Range The maritime to continental climatic change from west to east has a profound effect on regional vegetation patterns Most of the community types in the eastern North Cascades are closely related to those in the Rocky Mountains, southern Alaska and the southern Yukon whereas communities in the western North Cascades are more similar to communities in other west coast ranges Soils in the region include Entisols, Inceptisols, and Spodosols Physical properties are quite similar in most soils Organic matter, total cation exchange capacity, and pH generally decrease from west to east while exchangeable cations and nutrient levels are low throughout the region A fellfield—dry graminoid—mesic environmental gradient was examined on Grouse Ridge, Mt Baker High soil temperature and low soil moisture regimes were typical of the ridgetop fellfield During drought periods, on the vegetated portion of the slope, soil temperatures decreased and soil moisture stress increased with distance downslope; a reflection of increased plant cover and greater evapotranspiration towards the base of the slope Species at the base of the slope had reduced vigor and much lower leaf water potential than those upslope Phenological patterns were closely related to date of snowmelt and early—season temperature regimes along the gradient