Benthic invertebrate recolonization of small-scale disturbances in the littoral zone of a subtropical Florida lake

Construction of spawning beds by the exotic cichlid fish, Sarotherodon aurea, produces numerous small-scale disturbances in shallow Florida lakes. Two experimental methods were used to simulate these disturbances (containers filled with defaunated sediment and disturbed natural substratum) and to determine benthic invertebrate recolonization patterns and rates.Recolonization of experimental containers was rapid and densities of macroinvertebrates reached equilibrium with the control habitat by Day 6 following disturbance. However, Chironomidae and miscellaneous taxa usually were more abundant (p < 0.05) in the experimental containers, and Oligochaeta always were more abundant (p < 0.01) in the control. Species of the planktonically dispersed insects either attained equilibrium rapidly or showed significantly higher densities in the experimental containers (i.e. opportunistic species).In the second experimental approach, disturbance of natural substratum removed 91% of the benthic invertebrates. The common species of chironomids reached equilibrium by Day 6 but the two predominant oligochaetes, Limnodrilus and Pristina, reached equilibrium at 9 and 15 days respectively. For the entire community, similarity on Day 6 was 87.1% and over the remainder of the sample period averaged 86.8%. Chironomid instar analyses showed significantly higher proportions of early instars in the disturbed patch indicating that colonization is principally by younger organisms. Thus, small-scale disturbance in freshwater benthic communities may be more important in ordering the biomass or age-group structure than the numerical abundance.     

Wetlands and global climate change: the role of wetland restoration in a changing world

Global climate change is recognized as a threat to species survival and the health of natural systems. Scientists worldwide are looking at the ecological and hydrological impacts resulting from climate change. Climate change will make future efforts to restore and manage wetlands more complex. Wetland systems are vulnerable to changes in quantity and quality of their water supply, and it is expected that climate change will have a pronounced effect on wetlands through alterations in hydrological regimes with great global variability. Wetland habitat responses to climate change and the implications for restoration will be realized differently on a regional and mega-watershed level, making it important to recognize that specific restoration and management plans will require examination by habitat. Floodplains, mangroves, seagrasses, saltmarshes, arctic wetlands, peatlands, freshwater marshes and forests are very diverse habitats, with different stressors and hence different management and restoration techniques are needed. The Sundarban (Bangladesh and India), Mekong river delta (Vietnam), and southern Ontario (Canada) are examples of major wetland complexes where the effects of climate change are evolving in different ways. Thus, successful long term restoration and management of these systems will hinge on how we choose to respond to the effects of climate change. How will we choose priorities for restoration and research? Will enough water be available to rehabilitate currently damaged, water-starved wetland ecosystems? This is a policy paper originally produced at the request of the Ramsar Convention on Wetlands and incorporates opinion, interpretation and scientific-based arguments.     

The legacy of past climate and landscape change on species' current experienced climate and elevation ranges across latitude: a multispecies study utilizing mammals in western North America

Aim Elevation and climate ranges across latitude experienced by 21 wide‐ranging mammal species in western North America were summarized to examine two questions: (1) do populations in the northern and southern portions of a species’ range experience different climates or are environments selected to remain similar to climates at the core of ranges; and (2) how do species’ elevational ranges, experienced temperature seasonality and temperature ranges change across latitude? Given the larger effects of climate oscillations in the north vs. the south, a predicted outcome is for species to conserve climate niches across latitude and to show reduced climate and elevation ranges in the north. An alternative outcome is latitudinal niche diversification and increased climate variation in the north. Location Western North America. Methods The questions above were examined using a combination of species occurrence data bases, climate data bases, simple summaries of means and standard deviations and by testing summaries against random distributions across latitude for 21 mammal species from a variety of orders. Results The results showed that: (i) most species conserve their niche strongly or weakly given overall temperature gradients from north to south; (ii) seasonality experienced by species is relatively static until the highest latitudes despite directional trends across the region; and (iii) the elevation range and temperature variation that species experience decreases from south to north. Main conclusions Populations at range edges appear to partition environments to remain closer to temperature values similar to those at the core of the range. In addition, seasonality is not a likely explanatory factor of genetic diversity in latitudinal gradients. The data are instead more consistent with predictions that a combination of higher gene‐flow, increasing environmental instability and decreasing elevation gradients in the north compared to the south may lead to negative correlations between latitude and species’ climate variation. The results corroborate risks faced by northern mammal populations to global climate changes.     

Priority areas for the conservation of subtropical indigenous forest in southern Africa: a case study from KwaZulu-Natal

Southern Africa's subtropical forest biome, though small and highly fragmented, supports much of the region's biodiversity. With limited resources available for conservation and the exploitative use of forest escalating, identifying a network of priority forest reserves is important. We examine the distribution of forest birds, butterflies and mammals in KwaZulu-Natal, South Africa. Using an iterative algorithm we explore the efficiency of existing protected areas, species richness and rarity hotspots, prime forest sites (selected by forest area) and complementary networks as alternative approaches to priority reserve selection, as well as the potential use of indicator taxa. Existing protected areas represent 98% of species but are relatively inefficient in terms of area. Alternative selection criteria represent a high proportion of species (86–92%) and provide efficient bases for developing fully representative reserve networks. All species are represented within a network of 22 complementary quarter degree cells. This network includes several larger forests and existing protected areas and is recommended for priority conservation. Complementary networks identified separately for birds, butterflies and mammals overlap little, but each represents a high proportion of the remaining taxa, supporting their potential as representative 'indicator' taxa. The evolutionary history of the three main forest types in KwaZulu-Natal explains observed spatial patterns of alternative reserve networks. Priority areas are concentrated in scarp and coastal forest belts, regions of comparatively recent evolutionary activity with high species richness. Afromontane forest is older and less diverse, but its inclusion in any reserve network is necessary for the full representation of forest diversity.     

Modeling density dependence and climatic disturbances in caribou: a case study from the Bathurst Island complex, Canadian High Arctic

Peary caribou Rangifer tarandus pearyi is the northernmost subspecies of Rangifer in North America and endemic to the Canadian High Arctic. Because of severe population declines following years of unfavorable winter weather with ice coating on the ground or thicker snow cover, it is believed that density-independent disturbance events are the primary driver for Peary caribou population dynamics. However, it is unclear to what extent density dependence may affect population dynamics of this species. Here, we test for different levels of density dependence in a stochastic, single-stage population model, based on available empirical information for the Bathurst Island complex (BIC) population in the Canadian High Arctic. We compare predicted densities with observed densities during 1961–2001 under various assumptions of the strength of density dependence. On the basis of our model, we found that scenarios with no or very low density dependence led to population densities far above observed densities. For average observed disturbance regimes, a carrying capacity of 0.1 caribou km⁻² generated an average caribou density similar to that estimated for the BIC population over the past four decades. With our model we also tested the potential effects of climate change-related increases in the probability and severity of disturbance years, that is unusually poor winter conditions. On the basis of our simulation results, we found that, in particular, potential increases in disturbance severity (as opposed to disturbance frequency) may pose a considerable threat to the persistence of this species.