Regional species gains outpace losses across North American continental shelf regions

Aim

Although species richness globally is likely to be declining, patterns in diversity at the regional scale depend on species gains within new habitats and species losses from previously inhabited areas. Our understanding of the processes associated with gains or losses remains poor, including whether these events exhibit immediate or delayed responses to environmental change.

Location

The study focuses on nine temperate marine ecosystems in North America.

Time period

The study period varies by region, but overall encompasses observations from 1970 to 2014.

Major taxa studied

We identified regional gains and losses for 577 marine fish and invertebrate species.

Methods

From a total of 166,213 sampling events from bottom trawls across North America that informed 17,997 independent observations of species gains and losses, we built generalized linear mixed effects models to test whether lagged temperature can explain instances of gains and losses of marine fishes and invertebrates in North American continental shelf habitats.

Results

We found that gains were less likely in years with high seasonality, consistent with seasonal extremes as a strong constraint on species occurrence. Losses were also negatively associated with high seasonality, but the response was delayed by 3 years.

Main conclusions

Environmental conditions play a role in species occupancy across diverse temperate marine ecosystems. Immediate gains paired with delayed losses can drive transient increases in species richness during times of environmental change. Identifying the dynamics behind regional species gains and losses is an important step towards prediction of biodiversity changes across ecosystems.     

Models of competition in the chemostat with instantaneous and delayed nutrient recycling

Two models for competition of two populations in a chemostat environment with nutrient recycling are considered. In the first model, the recycling is instantaneous, whereas in the second, the recycling is delayed. For each model an equilibrium analysis is carried out, and persistence criteria are obtained. This paper extends the work done by Beretta et al. (1990) for a single species.Research partially supported by the Natural Sciences and Engineering Research Council of Canada, Grant NSERC A4823Research carried out at the University of Alberta while on a Canada-China Scholarly Exchange Program     

The measure of order and disorder in the distribution of species in fragmented habitat

Species distribution patterns within naturally fragmented habitat have been found to often exhibit patterns of pronounced nestedness. Highly predictable extinction sequences are implied by these nested species distribution patterns, thus the patterns are important to both the philosophy and practice of conservation biology. A simple thermodynamic measure of the order and disorder apparent in the nested patterns is described. The metric offers (i) a measure of the uncertainty in species extinction order, (ii) a measure of relative populational stabilities, (iii) a means of identifying minimally sustainable population sizes, and (iv) an estimate of the historical coherence of the species assemblage. Four presumptions govern the development of the metric and its theory: (i) the fragmented habitat was once whole and originally populated by a single common source biota, (ii) the islands were initially uniform in their habitat heterogeneity and type mix, and have remained so throughout their post-fragmentation history, (iii) no significant clinal (latitudinal) gradation exists across the archipelago so as to promote species turnover across the archipelago, and (iv) all species of interest are equally isolated on all islands. The violation of these conditions promotes species distributions which are idiosyncratic to the general extinction order expected in fragmentation archipelagos. While some random variation in extinction order is to be expected, idiosyncratic distributional patterns differ from randomness and are readily segregatable from such noise. A method of identifying idiosyncratic species and sites is described.     

Mutual exclusion versus coexistence for discrete competitive systems

Using discrete competition models where the density dependent growth functions are either all exponential or all rational, notwithstanding the complex interactions of the species, we establish an exclusion principle. Moreover, in a 2-species discrete competition model where the growth functions are exponential and rational, an example is given illustrating coexistence when our conditions are satisfied. We obtain an exclusion principle for this 2-species model for some choice of parameters.Research partially supported by funds provided by a Science and Education Grant to the USDA-Forest Service, Southeastern Forest Experiment Station, Population Genetics of Forest Trees Research Unit, Raleigh, North Carolina     

Respiratory quotient and ammonia quotient in Tilapia mossambica (Peters) with special reference to hypoxia and recovery

At oxygen concentrations below air saturation, R.Q. and A.Q. values of Tilapia mossambica increase with decrease in ambient oxygen at 30 and 35°C, indicating an increase in anaerobic metabolism and protein utilization. The recovery metabolism indicates that T. mossambica accumulates an oxygen debt at 30°C, which was not obvious at 35°C. The post-hypoxic oxygen consumption at 30°C is quite pronounced and the fish repays almost wholly the oxygen debt accumulated. At 30°C, R.Q. and A.Q. reach prehypoxic level immediately after exposure to high oxygenated water. In contrast to this, during recovery the first high R.Q. which is higher than unity and subsequent low R.Qs., almost as low as 0.5, suggest respectively that, anaerobic energy utilization persists and carbon dioxide is retained. The differences in the recovery metabolism of T. mossambica at the two temperatures may be due to changes in metabolism and pathways due to temperature. The recovery metabolism of T. mossambica suggests that energy derived anaerobically could proceed through other pathways than the conventional glycolytic way. The decrease in random activity during the hypoxic phase at 30 and 35°C may have a special significance for survival.From a thesis (M.P.M.) approved for the degree of Doctor of Philosophy, Madurai University, Madurai, India.From a thesis (M.P.M.) approved for the degree of Doctor of Philosophy, Madurai University, Madurai, India.     

Extinction risk, coloured noise and the scaling of variance

The impact of temporally correlated fluctuating environments (coloured noise) on the extinction risk of populations has become a main focus in theoretical population ecology. In this study we particularly focus on the extinction risk in strongly correlated environments. Here, we found that, in contrast to moderate auto-correlation, the extinction risk was highly dependent on the process of noise generation, in particular on the method of variance scaling. Such scaling is commonly applied to avoid variance-driven biases when comparing the extinction risk under white and coloured noise. We show that for strong auto-correlation often-used scaling techniques lead to a high variability in the variances of the resulting time series and thus to deviations in the subsequent extinction risk. Therefore, we present an alternative scaling method that always delivers the target variance, even in the case of strong auto-correlation. In contrast to earlier techniques, our very intuitive method is not bound to auto-regressive processes but can be applied to all types of coloured noises. We strongly recommend our method to generate time series when the target of interest is the effect of noise colour on extinction risk not obscured by any variance effects.     

Extinction and permanence of one-prey multi-predators of Holling type II function response system with impulsive biological control

In this paper, one investigates the dynamic behaviors of one-prey multi-predator model with Holling type II functional response by introducing impulsive biological control strategy (periodic releasing natural enemies at different fixed time). By using Floquet theorem and small amplitude perturbation method, it is proved that there exists an asymptotically stable pest-eradication periodic solution when the impulsive period is less than some critical value and permanence condition is established via the method of comparison involving multiple Liapunov functions. It is shown that multi-predator impulsive control strategy is more effective than the classical and single one.     

Extinction threat evaluation of endemic fig trees of New Caledonia: Priority assessment for taxonomy and conservation with herbarium collections

This article focuses on the relationship between priority-setting in conservation and in taxonomy. A simple and generally applicable scheme is presented based on prior quantitative extinction threat evaluation. In the main part of the study we describe the assessment of the herbarium voucher collection date time series of 21 endemic fig tree species of Ficus sect. Oreosycea (Moraceae). The fig tree assessment is then compared with the available IUCN Red List data and with the collection information on two other groups of endemic tree radiations in New Caledonia: ebonies of Diospyros sect. Maba (Ebenaceae) and the Iguanura palm lineage (Arecaceae). We find a remarkably low level of extinction threat evident in Ficus but a pronounced need to differentiate between true species rarity and putative rarity of potential taxonomic artifacts. To this end it is proposed how such numerical evaluations can be used to set future priorities for the assessment or validation of the taxonomic and conservation status of taxa. The limitations and implications of the evaluation are discussed and relevant criteria for a meaningful analysis of collection records are listed. Finally, putting our results on woody plants into perspective, we briefly review the general conservation situation and outlook of New Caledonia, acknowledging both its high conservation priority and potential. Abbreviations: Note that different IUCN threat category classifications have been in use during the last decade and that some of the cited categories and their abbreviations have changed (IUCN 1994, 2001).     

Pioneer exclusion in a one-hump discrete pioneer-climax competitive system

One-hump maps as single species pioneer and climax ecological models confirm the expected pioneer exclusion in an uninterrupted two dimensional discrete pioneer-climax competition model. Other dynamic situations occur in such models. In particular a mutual exclusion principle is presented as a mathematical theorem.     

19th century woodland structure controls stand-scale epiphyte diversity in present-day Scotland

Axioms developed from island biogeography theory (i.e. species–area relationships, effects of fragmentation and isolation) are central to the development of conservation strategy. Within this context, the 'extinction debt' hypothesis brings into question an often assumed relationship between species richness and present-day spatial habitat structure (i.e. extent, fragmentation), suggesting instead that the richness and composition of biological communities may lag behind spatial changes in habitat. We examined evidence for an extinction debt among epiphytic lichens, a highly diverse biological group of significant conservation concern. Using sites in Scotland, we compared epiphyte species richness in smaller-scale habitat units (aspen stands) to larger-scale woodland structure (extent and fragmentation) measured at two spatial scales (1 km² and 4 km²) and for two timeframes, modern (1990s to 2000s) and historic (1860s to 1880s). Species richness was positively related to woodland extent and negatively related to woodland fragmentation; however, richness was explained better by historic woodland structure at a 1-km² scale, than by modern woodland structure. The results indicate: (1) a coupling of stand-scale epiphyte assembly and dynamics of the wider woodland ecosystem, and (2) a significant lag in the response of epiphyte species richness to habitat spatial structure. However, the effect of spatial habitat structure is different between species groups with contrasting traits. The effect of decreasing woodland extent on epiphyte richness is generally more severe for microlichens (comprising a greater number of rare and specialist species) than the more generalist macrolichens.