Fundamental Ecological Processes Research Articles

Land-Use History as Long-Term Broad-Scale Disturbance: Regional Forest Dynamics in Central New England

Human land-use activities differ from natural disturbance processes and may elicit novel biotic responses and disrupt existing biotic-environmental relationships. The widespread prevalence of land use requires that human activity be addressed as a fundamental ecological process and that lessons from investigations of land-use history be applied to landscape conservation and management. Changes in the intensity of land use and extent of forest cover in New England over the past 3 centuries provide the opportunity to evaluate the nature of forest response and reorganization to such broad-scale disturbance. Using a range of archival data and modern studies, we assessed historical changes in forest vegetation and land use from the Colonial period (early 17th century) to the present across a 5000 km2 area in central Massachusetts in order to evaluate the effects of this novel disturbance regime on the structure, composition, and pattern of vegetation and its relationship to regional climatic gradients. At the time of European settlement, the distribution of tree taxa and forest assemblages showed pronounced regional variation and corresponded strongly to climate gradients, especially variation in growing degree days. The dominance of hemlock and northern hardwoods (maple, beech, and birch) in the cooler Central Uplands and oak and hickory at lower elevations in the Connecticut Valley and Eastern Lowlands is consistent with the regional distribution of these taxa and suggests a strong climatic control over broad-scale vegetation patterns. We infer from historical and paleoecological data that intensive natural or aboriginal disturbance was minimal in the Uplands, whereas infrequent surface fires in the Lowlands may have helped to maintain the abundance of central hardwoods and to restrict the abundance of hemlock, beech, and sugar maple in these areas. The modern vegetation is compositionally distinct from Colonial vegetation, exhibits less regional variation in the distribution of tree taxa or forest assemblages defined by tree taxa, and shows little relationship to broad climatic gradients. The homogenization of the vegetation, disruption of vegetation-environment relationships, and formation of new assemblages appear to be the result of (a) a massive, novel disturbance regime; (b) ongoing low-intensity human and natural disturbance throughout the reforestation period to the present; (c) permanent changes in some aspects of the biotic and abiotic environment; and (d) a relatively short period for forest recovery (100–150 years). These factors have maintained the regional abundance of shade intolerant and moderately tolerant taxa (for example, birch, red maple, oak, and pine) and restricted the spread and increase of shade-tolerant, long-lived taxa such as hemlock and beech. These results raise the possibility that historical land use has similarly altered vegetation-environment relationships across broader geographic regions and should be considered in all contemporary studies of global change.

Life on the edge: insect ecology in arctic environments.

The restricted Arctic insect fauna is usually explained by a lack of recolonization since the last glacial period, inadequate supply of suitable resources, or insufficient adaptation to such a harsh environment. These hypotheses and others that attempt to explain the latitudinal gradient of species distributions and abundance are reviewed. Arctic habitats available to insects are strongly heterogeneous, requiring a similarly diverse array of adaptive responses, characteristic of those species that have colonized and survived in such a stressful climate. Important adaptations in morphology (size, wings), behavior (activity patterns, thermoregulation), life cycles, and ecophysiology (cold hardiness, anaerobiosis, desiccation resistance) are discussed. The current focus of global climate change research on polar regions is identified, particularly the opportunity to study fundamental ecological processes and spatial dynamics in the relatively simple Arctic ecosystems.

Hierarchical characterization of canopy architecture for boreal forest

Canopy architecture, the geometric organization of aboveground vegetation, provides an essential link between patterns observable by remote sensing and fundamental ecological processes. As part of the international Boreal Ecosystem‐Atmosphere Study (BOREAS); (1) we developed a hierarchical approach for sampling canopy architecture, and (2) we acquired a comprehensive data set for characterizing canopy architecture for the major BOREAS study sites. The approach involves a series of four sets of measurements at different spatial scales, ranging from the ecosystem to the leaf level: (1) regional characterization, involving measurements of the climate, ecosystem, and landscape features; (2) stand characterization, involving measurements of crown geometry (diameter at breast height (DBH), height, and crown extent), individual tree location, and understory cover; (3) tree vectorization, involving detailed sampling of the three‐dimensional distribution of canopy elements and crown form; and (4) characterization of canopy geometry as seen from beneath, involving acquisition of a multitemporal catalog of hemispherical photographs. The last three sets of measurements were then used to reconstruct the three‐dimensional geometry of the canopy. By comparing simulated hemispherical views upward from beneath this reconstructed canopy with in situ hemispherical photographs, the methodological approach was validated. Simulated photographs faithfully reproduced patterns observed for in situ hemispherical photographs, in particular, for gap fraction distributions of the middle ranges of zenith angles (20°–70°). Moreover, simulation of the gap fraction for this middle portion of the zenith angle was insensitive to exact mapping of the stand. The hierarchical data acquisition approach, involving mapping of tree locations and tree reconstruction, permits realistic representation of canopy material distribution. Our approach and our comprehensive data set provide a solid basis from which to integrate data gathered at the stand and tree scales, and a powerful tool for the simulation of the light regime anywhere in the canopy.

Prey selection by sparrowhawks,Accipiter nisus: relative predation risk for breeding passerine birds in relation to their size, ecology and behaviour

Predation is a fundamental ecological process, but there are few studies of predation risk for adult, breeding birds. In this study, we quantified Relative Predation Risk (RPR) for 46 species of passerine birds preyed on by sparrowhawks during the breeding season in south-western Sweden. The sparrowhawk is a major predator of smaller birds in Eurasian forests and woodland. Near nesting hawk pairs, prey abundance was estimated by line transects. From prey remains at hawk nests, we estimated the frequency of prey species in the diet of hawks. For each hawk pair, RPR values for different prey species were calculated. The mean RPR for each prey species, based on hawk pairs as sample units, indicated degree of overrepresentation (positive RPR) or underrepresentation (negative RPR) of the prey in the diet. Prey species with a high positive RPR nested mainly near human habitations (villages or towns), at forest edges and in farmland. However, there were marked seasonal changes in RPR. Forest birds, such as the goldcrest and wren, had the highest RPR in April. Later, the hawks seemed to hunt mainly in the habitats mentioned above, where prey were more abundant or easier to catch, resulting in increasing RPR for the house sparrow, yellowhammer, greenfinch and other species. RPR values were analysed in relation to prey body size (mass) and relative density, as well as prey foraging height and nest height (categorized from the literature). In addition, the mean perch height and mean exposure of prey species were quantified in the field. Most predation was due to the smaller male hawks, providing food for their mates and young, RPR increased with prey body size up to a mass of about 40 g, then declined with increasing body size (larger prey being more difficult to catch), RPR decreased with increasing relative density of prey species. Nest height was not correlated with RPR, but foraging height seems to be an important factor: RPR decreased with increasing foraging height. A similar result was found for mean perch height, when larger prey (over 40 g) and singing individuals were excluded from the field data. RPR increased with mean exposure of prey species when larger prey and singing birds were excluded; a combination of perch height and exposure improved the correlation with RPR. Singing birds were generally perched high in the vegetation and may not suffer high predation risk, contrary to common belief. The results of this study are discussed in relation to temporal and geographical variation in RPR and antipredator adaptations in passerine birds.

On the Practice of Ecology

Despite inspiration from their subject and an unwavering belief in its importance, ecologists often seem to be in a state of self-doubt about progress in ecology. When we observe the advances occurring in other fields, such as cellular and molecular biology, we cannot help noting that our own science does not appear to be progressing in the same way. We are debating many of the same issues today that we were decades ago. While there appears to be progress on some specific questions, we have not observed major advances in our understanding of fundamental ecological processes. Recently, an author of one of the best and most widely used general ecology textbooks told me that when he and his coauthors sat down to do the second edition of their book, they found very little that was substantively new in ecology in the years since the publication of their first edition. In contrast, a colleague who is the author of one of the best textbooks in developmental biology tells me that he has to rewrite major sections of his text for every new edition because the field is moving so fast. Frustration with the apparent lack of progress has led numerous ecologists to question the way scientific research in ecology is done (e.g. Dayton 1979; Pielou 1981; Simberloff 1981, 1983; Hall 1988; Keddy 1989; Peters 1991). The criticisms of ecology have emerged primarily from within the field, often from established and successful researchers. This essay attempts to outline a useful critique of ecological research. The motivation is not philosophical issues of epistemology, but the more practical problem of progress within our science. Many ecologists attribute the lack of progress in ecological science to the nature of the 'beasts,' not to methodological issues. It is unclear to what extent many ecological phenomena are controlled and therefore predictable. For example, current ideas that communities may not be near equilibrium, and the recent re-emphasis on the necessary role of historical explanations (e.g. Gould 1986; Ricklefs & Schluter 1993) mean that ecological systems will never be as predictable as physical or chemical processes, but many researchers think that the way ecology is done could be part of the problem. I will argue for a general critique of ecological research based on principles that are widely held among ecologists. From this critique we can make some modest proposals for improving the way ecological research is pursued. These principles include 1 the need for predictive models and testable explanatory theories; 2 an appreciation of the role of natural history vis a vis ecology; 3 the need for pluralism and diversity, and especially for new approaches, within our young scientists.

Ecological effects of hepatotoxic cyanobacteria

AbstractMany species of cyanobacteria produce hepatotoxic peptides called microcystins. Toxic cyanobacteria have caused fish, wildlife, and cattle mortality in many countries, but the distribution and fate of toxins and their ecological effects are poorly known. Toxic cyanobacteria may affect sensitive organisms and populations, but also fundamental ecological processes, e.g., primary production and microbial activity. Many studies show negative effects of cyanobacteria on zooplankton, but information on the type and quantity of toxin(s) involved is usually missing. Mussels accumulate peptide toxins but accumulation in other organisms remains to be studied. Cyanobacterial blooms often affect the littoral zones, which are important reproduction and feeding areas for fish and birds.

Oceanic habitat differences in The North Pacific

A pronounced faunal boundary and a gradient of Zooplankton biomass exist in the oceanic North Pacific. A summer and a winter set of observations were taken on transects normal to these latitudinal boundaries. The resulting data have been analysed both in terms of the measured variables from either side of the boundary area and of their interrelationships. Great differences between three major habitats in concentrations of nutrients, standing crops of phyto- and Zooplankton, average temperatures and average salinities have been demonstrated. Furthermore, the type of seasonal changes in these variables differed between habitats. In general, variations in Zooplankton abundance are related to plant abundance in the summer and phosphate-phosphorus in the winter. Horizontal and vertical temperature gradients are not strongly related to variations in Zooplankton abundance nor is the dissolved plus particulate organic carbon concentration; however, there is evidence that the dissolved plus particulate organic carbon does not behave as a conservative property either within or below the mixed layer. There appear to be some qualitative differences in fundamental ecological processes between these habitats.

The Negro in Bahia, Brazil

STUDENTS of plant, animal, and human ecology are all particularly interested in dispersion and in migration and settlement which dispersion involves. Eugenius Warming defined oecology as an attempt to discover what species commonly associate together, why they congregate to form definite communities and what means they employ to adapt their external and internal structure so as to more effectively utilize their environment.' Richard Hesse, W. C. Allee, and Karl Schmidt have given particular attention to study of animal distribution, or to what they call zoogeography.2 Writers in field of human ecology similarly recognize migration and settlement as quite fundamental processes. But since there have been, in addition to obvious physical movement and visible economic influences, other developments, certain consequences of a cultural order, occasioned by and intimately bound up with these fundamental ecological processes, other students, particularly those concerned with cultural change, are equally interested in migration and settlement. For example, Karl Mannheim refers to skepticism regarding the general and eternal validity of one's own thought forms which social mobility incidental to recent human dispersion has introduced into our present intellectual life.3 We are concerned here with one of greatest, in extent and effect, population movements in all history: namely, migrations and series of settlements associated with expansion of western Europe. During 500 years since Portuguese first began pushing their way around continent of Africa toward rich resources of East, this outward dispersal has been bringing European peoples and European cultures into contact with native peoples and native cultures throughout habitable world. Park,4 McKenzie,5 and other writers have indicated in considerable detail chain of effects which this expansion has occasioned and which, in fact, has ushered in all that is characteristic of modern world. The outward expansion of Europe can be considered as a definite, distinct historical process. It is unitary; it constitutes an epoch which has