Michael R. Sutherland

Inferring ecological relationships from the edges of scatter diagrams: Comparison of regression techniques

Scatter diagrams have historically proved useful in the study of associative relationships in ecology. Several important ecological questions involve correlations be- tween variables resulting in polygonal shapes. Two examples that have received consid- erable attention are patterns between prey size and predator size in animal populations and the relationship between animal abundance and body size. Each is typically illustrated using scatter diagrams with upper and lower boundaries of response variables often changing at different rates with changes in the independent variables. Despite recent statistical contri- butions that have stimulated an interest in characterizing the limits of a variable, a consensus on an appropriate methodology to quantify the boundaries of scatter diagrams has not yet been achieved. We tested regression techniques based on least squares and least absolute values models using several independent data sets on prey length and predator length for piscivorous fishes and compared estimated slopes for consistency. Our results indicated that least squares regression techniques were particularly sensitive to outlying y values and irregularities in the distribution of observations, and that they frequently produced incon- sistent estimates of slope for upper and lower bounds. In contrast, quantile regression techniques based on least absolute values models appeared robust to outlying y values and sparseness within data sets, while providing consistent estimates of upper and lower bound slopes. Moreover, the use of quantile regression eliminated the need for an excess of arbitrary decision-making on the part of the investigator. We recommend quantile regression as an improvement to currently available techniques used to examine potential ecological relationships dependent upon quantitative information on the boundaries of polygonal re- lationships.

Teeth, brains, and primate life histories

This paper explores the correlates of variation in dental development across the order Primates. We are particularly interested in how 1) dental precocity (percentage of total postcanine primary and secondary teeth that have erupted at selected absolute ages and life cycle stages) and 2) dental endowment at weaning (percentage of adult postcanine occlusal area that is present at weaning) are related to variation in body or brain size and diet in primates. We ask whether folivores have more accelerated dental schedules than do like-sized frugivores, and if so, to what extent this is part and parcel of a general pattern of acceleration of life histories in more folivorous taxa. What is the adaptive significance of variation in dental eruption schedules across the order Primates? We show that folivorous primate species tend to exhibit more rapid dental development (on an absolute scale) than comparably sized frugivores, and their dental development tends to be more advanced at weaning. Our data affirm an important role for brain (rather than body) size as a predictor of both absolute and relative dental development. Tests of alternative dietary hypotheses offer the strongest support for the foraging independence and food processing hypotheses.

SUSCEPTIBILITY OF SALT MARSHES TO NUTRIENT ENRICHMENT AND PREDATOR REMOVAL

Salt marsh ecosystems have been considered not susceptible to nitrogen overloading because early studies suggested that salt marshes adsorbed excess nutrients in plant growth. However, the possible effect of nutrient loading on species composition, and the combined effects of nutrients and altered species composition on structure and function, was largely ignored. Failure to understand interactions between nutrient loading and species composition may lead to severe underestimates of the impacts of stresses. We altered whole salt marsh ecosystems (;60 000 m 2 /treatment) by addition of nutrients in flooding waters and by reduction of a key predatory fish, the mummichog. We added nutrients (N and P; 15-fold increase over ambient conditions) directly to the flooding tide to mimic the way anthropogenic nutrients are delivered to marsh ecosystems. Despite the high concentrations (70 mmol N/L) achieved in the water column, our annual N loadings (15-60 g Nm � 2 � yr � 1 ) were an order of magnitude less than most plot-level fertilization experiments, yet we detected responses at several trophic levels. Preliminary calculations suggest that 30-40% of the added N was removed by the marsh during each tidal cycle. Creek bank Spartina alterniflora and high marsh S. patens production increased, but not stunted high marsh S. alterniflora. Microbial production increased in the fertilized creek bank S. alterniflora habitat where benthic microalgae also increased. We found top-down control of benthic microalgae by killifish, but only under nutrient addition and in the opposite direction (increase) than that predicted by a fish-invertebrate-microalgae trophic cascade. Surprisingly, infauna declined in abundance during the first season of fertilization and with fish removal. Our results demonstrate ecological effects of both nutrient addition and mummichog reduction at the whole-system level, including evidence for synergistic interactions.

Spatial and temporal arrival patterns of Madagascar's vertebrate fauna explained by distance, ocean currents, and ancestor type

How, when, and from where Madagascars vertebrates arrived on the island is poorly known, and a comprehensive explanation for the distribution of its organisms has yet to emerge. We begin to break that impasse by analyzing vertebrate arrival patterns implied by currently existing taxa. For each of 81 clades, we compiled arrival date, source, and ancestor type (obligate freshwater, terrestrial, facultative swimmer, or volant). We analyzed changes in arrival rates, with and without adjusting for clade extinction. Probability of successful transoceanic dispersal is negatively correlated with distance traveled and influenced by ocean currents and ancestor type. Obligate rafters show a decrease in probability of successful transoceanic dispersal from the Paleocene onward, reaching the lowest levels after the mid-Miocene. This finding is consistent with a paleoceanographic model [Ali JR, Huber M (2010) Nature 463:653–656] that predicts Early Cenozoic surface currents periodically conducive to rafting or swimming from Africa, followed by a reconfiguration to present-day flow 15–20 million years ago that significantly diminished the ability for transoceanic dispersal to Madagascar from the adjacent mainland.

Atlantic Sturgeon Marine Distribution and Habitat Use along the Northeastern Coast of the United States

Abstract Though the distribution of Atlantic sturgeon Acipenser oxyrinchus is relatively well known in freshwater and estuarine habitats in the northern portion of their range, their distribution in marine habitats is poorly understood. Sturgeon migrate into marine waters to forage between spawning events and probably maintain gene flow between river populations by entering nonnatal river systems to spawn. While at sea, they are captured in commercial fishing gears. We investigated data collected by onboard fishery observers to determine the occurrence and habitat preference of Atlantic sturgeon off the northeastern coast of the United States. Sturgeon distributions were based on monitored fishing trips over the period 1989–2000 and referenced to local bathymetry and sediment data. The results show that peak sturgeon captures along the coast were approximately bracketed by isobaths ranging from 10 to 50 m. Sturgeon were present more frequently on gravel and sand sediment types and were associated with spe...

Imperfect Isolation: Factors and Filters Shaping Madagascar's Extant Vertebrate Fauna

Analyses of phylogenetic topology and estimates of divergence timing have facilitated a reconstruction of Madagascar’s colonization events by vertebrate animals, but that information alone does not reveal the major factors shaping the island’s biogeographic history. Here, we examine profiles of Malagasy vertebrate clades through time within the context of the island’s paleogeographical evolution to determine how particular events influenced the arrival of the island’s extant groups. First we compare vertebrate profiles on Madagascar before and after selected events; then we compare tetrapod profiles on Madagascar to contemporary tetrapod compositions globally. We show that changes from the Mesozoic to the Cenozoic in the proportions of Madagascar’s tetrapod clades (particularly its increase in the representation of birds and mammals) are tied to changes in their relative proportions elsewhere on the globe. Differences in the representation of vertebrate classes from the Mesozoic to the Cenozoic reflect the effects of extinction (i.e., the non-random susceptibility of the different vertebrate clades to purported catastrophic global events 65 million years ago), and new evolutionary opportunities for a subset of vertebrates with the relatively high potential for transoceanic dispersal potential. In comparison, changes in vertebrate class representation during the Cenozoic are minor. Despite the fact that the island’s isolation has resulted in high vertebrate endemism and a unique and taxonomically imbalanced extant vertebrate assemblage (both hailed as testimony to its long isolation), that isolation was never complete. Indeed, Madagascar’s extant tetrapod fauna owes more to colonization during the Cenozoic than to earlier arrivals. Madagascar’s unusual vertebrate assemblage needs to be understood with reference to the basal character of clades originating prior to the K-T extinction, as well as to the differential transoceanic dispersal advantage of other, more recently arriving clades. Thus, the composition of Madagascar’s endemic vertebrate assemblage itself provides evidence of the islands paleogeographic history.

Developing an understanding of lean thinking in process industries

The research described in this article has set out to determine the extent to which lean thinking is being adopted as a manufacturing philosophy by process industries. It concerns the application and examination of key lean manufacturing principles, namely, the alignment of production with demand, the elimination of waste, the integration of suppliers (IS) and the creative involvement of the workforce in improvement activities, to a range of process industry types based on Dennis and Merediths taxonomy of process industry transformation systems [Dennis, D. and Meredith, J., 2000a. An empirical analysis of process industry transformation systems. Management Science, 46 (8), 1085–1099]. Seventy-nine process industry product streams across 62 sites were studied. In addition, a five-site investigative field study was also undertaken. The findings demonstrate that lean practices associated with the elimination of waste are consistently used for improving manufacturing performance throughout the taxonomy of process industries but practices associated with other lean principles are inconsistently applied. In addition, explanations are provided on the appropriateness of lean thinking as a manufacturing philosophy and a strategy for improving manufacturing performance in different process industry types, and on the extent to which lean principles and practices are dependent on the characteristics of process industry transformation systems.

Dental Ontogeny and Life-History Strategies: The Case of the Giant Extinct Indroids of Madagascar

While investigating ecogeographic size variation in the extant and extinct lemurs of Madagascar (Albrechtet al.1990; Godfrey et al.1990), one of us (LRG) noted the occurrence in the collections of the Academie Malgache of several unusually small demimandibles of Mesopropithecus an extinct “sloth lemur” (or palaeopropithecid) from southwest Madagascar. The specimens appeared, at first glance, to belong to adults; all of the permanent teeth were fully erupted. But the jaws were little more than two-thirds the size of those of adult Mesopropithecus globiceps from the same localities. They did not appear to belong to a new and smaller species of Mesopropithecus because the teeth were identical in size and morphology to those of M.obiceps.

Causes and Economic Effects of Mortality in Livestock Guarding Dogs

We assessed causes of pre-senile mortality among working guarding dogs, and its effects on their manrgement and cost. A population of 449 livestock guarding dogs in 31 states showed no differences in mortality due to breed or sex, but dogs working on open rangelands died more frequently (p<.OOl) than those working on farms or fenced ranches. Half of the farm dogs died before they reached 38 months of age, by which time nearly three-quarters of the open rangelands dogs had succumbed. Accidents accounted for over half the deaths, culling for inappropriate behavior accounted for one-third, and diseases for 9%. High accident and culling rates in young dogs substantially increased the cost of this predator control technique. However, we found 2 main areas where corrective measures can be applied: (1) increasing the awareness among producers that accidents are a main cause of deaths especially during the dogs’ first 30 months of age; and (2) reducing the number of culls by improving the genetics of the dogs and by training producers to manage them. Eurasian livestock guarding dogs (Canis familiaris) can reduce or eliminate predation on sheep (Ovis aries) and goats (Capra hireus) on farms and ranches in the United States (Coppinger et al. 1983a,b; Green and Woodruff 1983a). Such reduction depends on dogs being attentive and trustworthy. Dogs deficient in either of those attributes are unsuccessful. Methods of predator control must be economical to be useful. Although guarding dogs are proving to be of reasonable cost, producers need to be aware of factors that can rapidly change the economic picture. Green et al. (1984) estimated dollar costs of guarding dogs and suggested that ability to deter predators and longevity are additional factors that influence costs relative to benefit. We examined the effect of ability and longevity on working guarding dogs. Specifically, we looked at: (1) the duration of guarding behavior, which is partially dependent upon the life span of the dog, and (2) the percentage of dogs that show appropriate guarding behavior. The longer a dog lives, the more cost-effective it will become, because the costs of purchase and training can be amortized over a longer period. Moreover, a longer life span makes the generally ineffective juvenile months a smaller percentage of the total. We assessed causes of pre-senile mortality among working guarding dogs, and its effects on their management and cost. In addition, we developed actuarial statistics that will assist producers, researchers, veterinarians, and breeders in keeping track of the age structure of a population of working guardians, and in planning for replacement animals.

Heterochronic Approaches to the Study of Locomotion

Despite the advances that have been made in documenting ontogenetic changes in primate skeletal morphology, relatively little is known about the ontogeny of locomotor behavior. Even less is known about differences among behavioral developmental trajectories of closely related species. The study of evolutionary changes in developmental trajectories is the purview of heterochrony. Heterochrony is generally defined as the study of perturbations and displacements in existing ontogenetic pathways caused by changes in developmental timing and rates. As such, it has been conceived by some researchers (e.g., Gould, 1977; Raff et al., 1990; Zelditch and Fink, 1996; Rice, 1997) as narrowly encompassing only a subset of possible evolutionary shifts in ontogeny, and by others (e.g., McKinney and McNamara, 1991) as all-inclusive. The goal of heterochrony is to understand the proximate causes of differences among adult phenotypes of closely related species. This entails understanding how, through development, morphology and behavior emerge, and how developmental trajectories themselves evolve. Applied to the study of locomotion, it means understanding the evolutionary basis for variation, if any, in the ontogeny of positional behavior, and its relation to the ontogeny of form.