Persistent Controversy in Statistical Approaches in Wildlife Sciences: A Perspective of Students

ABSTRACT The controversy over the use of null hypothesis statistical testing (NHST) has persisted for decades, yet NHST remains the most widely used statistical approach in wildlife sciences and ecology. A disconnect exists between those opposing NHST and many wildlife scientists and ecologists who conduct and publish research. This disconnect causes confusion and frustration on the part of students. We, as students, offer our perspective on how this issue may be addressed. Our objective is to encourage academic institutions and advisors of undergraduate and graduate students to introduce students to various statistical approaches so we can make well-informed decisions on the appropriate use of statistical tools in wildlife and ecological research projects. We propose an academic course that introduces students to various statistical approaches (e.g., Bayesian, frequentist, Fisherian, information theory) to build a foundation for critical thinking in applying statistics. We encourage academic advisors to become familiar with the statistical approaches available to wildlife scientists and ecologists and thus decrease bias towards one approach. Null hypothesis statistical testing is likely to persist as the most common statistical analysis tool in wildlife science until academic institutions and student advisors change their approach and emphasize a wider range of statistical methods.     

Leukemia; duration of life in children treated with corticotropin and cortisone

The average duration of survival of 15 cases of childhood leukemia treated with corticotropin and cortisone was 6.8 months. This survival was the same as observed among 59 children who received no treatment, or treatment with x-ray, or blood transfusion alone. Despite the fact that objective evidence of remission was observed in 7 of 15 children treated with corticotropin and cortisone, the remissions were not reflected by a longer duration of life. Treatment of childhood leukemia with corticotropin and cortisone appears to be a palliative measure, without significant effect on the duration of life.     

Is the pollen‐limited mistletoe Peraxilla tetrapetala (Loranthaceae) also seed limited?

Abstract Seed production in the endemic New Zealand mistletoe Peraxilla tetrapetala (Loranthaceae) has been shown to be consistently pollen limited, but to date there has been no test of whether the species is also seed limited. If it is not seed limited, then pollen limitation may have no effect on population size. We tested for seed limitation by sowing seeds onto host trees at high and low densities at two sites, and following survival for up to 69 months. Our rationale was that unless there is strong density‐dependent seedling mortality sufficient to negate increases in seed supply, the species would be seed limited. We simultaneously measured pollen limitation at both sites using pollen augmentation. Peraxilla tetrapetala was strongly pollen limited at both sites over 7 years at Ohau (mean Pollen Limitation Index 0.62), and 12 years at Craigieburn (mean PLI 0.44), before and during the seed‐limitation study. There was no significant overall negative effect of density on survival in sown P. tetrapetala seeds over 42–69 months. There was a significant positive effect: seeds were more likely to adhere to branches when sown at high densities. This initial advantage to high‐density seeds was gradually eroded by slightly (but non‐significantly) lower survival rates of adhered seeds at high density. By the end of the study there was no significant difference in overall survival in high and low density plantings. This means that P. tetrapetala was apparently both pollen limited and seed limited at both our sites. Hence, reduced densities of native bird pollinators caused by introduced mammalian carnivores are likely to reduce the density of adult mistletoes in the next generation. However, the generality of this result may be affected by the fact that mistletoes do not have a dense ‘seedling shadow’ under the parent mistletoe.     

Mistletoe fruit‐colour polymorphism and differential success in a habitat mosaic

Abstract Polymorphisms in fruit colour are common in nature, but mechanistic explanations for the factor(s) responsible for their maintenance are for the most part lacking. Past studies have focused on frugivore colour preferences and fruit removal rates, but until recently there has been no evidence that these factors are responsible for the maintenance of the polymorphisms. For other types of genetic polymorphisms, habitat heterogeneity has been shown to play a role in their maintenance. Here we test the habitat heterogeneity hypothesis for a polymorphic New Zealand mistletoe. We show that red‐fruited and orange‐fruited morphs of the mistletoe Alepis flavida (Hook. F) Tiegh. (Loranthaceae) differ in their growth, mortality and flowering on forest edges and in forest interior. Red‐fruited morphs, which are preferred by dispersers, grew, survived and flowered as well as orange‐fruited morphs on edges, whereas orange‐fruited morphs had much greater growth, survival, and flowering than red‐fruited morphs in the forest interior. This is the first evidence that habitat‐specific differences in growth and survival may contribute to maintaining fruit‐colour polymorphisms.     

Precocene is not a specific antigonadotropic agent in adult female Aedes aegypti

ABSTRACT. In the mosquito, Aedes aegypti , other workers have shown that prior to blood-feeding a pre-vitellogenic period ensues manifested by the growth and differentiation of ovarian follicles. This results in resting stage follicles which will then complete ovarian development after the blood-meal. Allatectomy of newly emerged females prevents follicles from reaching their resting stage and such follicles do not undergo subsequent vitellogenesis after blood-feeding. Precocene II, a plant substance which effectively prevents ovarian development in Oncopeltus fasciatus by causing the irreversible degeneration of the corpus allatum, was applied to newly emerged mosquitoes, and at various times after blood-feeding. Sublethal doses of precocene applied 1 h after adult emergence had no effect on pre-vitellogenic follicular development and did not prevent yolk deposition after the blood-meal. Precocene applied after blood-feeding had two major effects. When administered early, it inhibited trypsin synthesis and retarded ovarian maturation. Animals exposed to it later, exhibited abnormal oviposition. It is proposed that precocene II does not act as an antigonadotropic agent in adult Aedes aegypti , but that it does induce a general toxic state in treated animals.     

Abundance,species richness and feeding preferences of introduced molluscs in native grasslands of Victoria,Australia

Abstract Introduced molluscs have invaded endangered, remnant native grasslands of south‐eastern Australia, but few studies have investigated their distribution, abundance or potential impact. Molluscs were surveyed in grassland sites across an urban to rural transect west of Melbourne, Australia. It was confirmed that several introduced mollusc species have invaded these areas. Three snail and five slug species were identified, none of which was native to Australia. The most common species was the brown field slug (Deroceras panormitanum). Mollusc capture and species richness were positively related to the degree of urbanization in the surrounding landscape. There was also a negative relationship with fire frequency. Feeding trials revealed selective herbivory by the black‐keeled slug (Milax gagates) among native plants. Anecdotal evidence that variable glycine (Glycine tabacina) and button wrinklewort (Rutidosis leptorrhynchoides) are palatable to molluscs was supported. Mollusc herbivory may potentially lead to reduced fitness of palatable species, and changes in community composition and structure.     

Impacts of fine sediment addition to tussock, pasture, dairy and deer farming streams in New Zealand

1. Increased fine sediment input caused by agricultural development is expected to act as a stressor for stream ecosystems. In a large‐scale field experiment, we added fine river sand to 50‐m reaches of three second‐order streams in each of four categories of catchment development (ungrazed tussock grasslands, grazed pasture, dairying and deer farming) and measured the responses of macroinvertebrates and aquatic moss. 2. Before addition, fine sediment cover differed between land uses, being lowest in tussock (7%), intermediate in pasture (30%) and dairy (47%) and highest in deer streams (88%). Sediment addition increased cover by one land‐use category (e.g. augmented sediment cover in tussock streams was similar to pre‐existing cover in pasture streams), and cover remained high in impact reaches (compared with controls) throughout the 5‐week experiment. Sediment addition did not change concentrations of phosphate, nitrate and ammonium, which were generally highest in dairy streams and lowest in tussock streams. 3. Aquatic mosses (most common in tussock, absent in dairy and deer), invertebrate density (highest in deer, lowest in tussock), taxon richness (highest in pasture, lowest in deer) and diversity (highest in pasture and tussock, lowest in dairy and deer) all differed between land uses. Sediment addition resulted in reductions of moss cover, invertebrate taxon richness and richness of Ephemeroptera, Plecoptera and Trichoptera in impact relative to control reaches. 4. The impact of sediment addition was strongest in pasture streams where pre‐existing sediment cover was moderate and richness and diversity of the invertebrate community highest. However, even in the already sediment‐rich and species‐poor deer streams, density of one common taxon was reduced significantly by sediment addition, and another two were affected in the same way in dairy streams, the second‐most intense land use. 5. Our experiment has disentangled the impact of sediment addition from other concomitant land‐use effects that could not be reliably distinguished in previous research, which has mainly consisted of correlative studies or unrealistically small‐scale experiments.