Regrowth or dispersal? Recovery of a freshwater red alga following disturbance at the patch scale

Abstract Disturbance is an important factor in species coexistence. Disturbance models require knowledge about whether disturbed patches must be colonized anew from dispersal or whether species left behind can dominate, hence altering recovery trajectories of patches. The red, filamentous alga Audouinella hermannii Roth is a common macroalgal species present at sites in the Steavenson River, a stony, upland stream in south‐eastern Australia. We conducted an experiment in which we contrasted the recovery trajectory of the alga on overturned rocks compared with those that were not overturned, and for rocks that had remnants of the alga left behind compared with others where the alga was scrubbed off completely. Rocks had either a rough or smooth texture. Experimental rocks were set out in riffles and algal recovery monitored in 8 × 8 cm quadrats at approximately 4–6 weekly intervals for 8 months. We found that overturning caused a lasting impact on A. hermannii cover, whereas rocks that were abraded by scrubbing recovered very quickly, suggesting that this alga can re‐grow quickly from fragments (a result confirmed by a second experiment). Both surface texture and resident algae affected recovery on abraded substrata. Quadrats surrounded by resident algae on rough‐textured rocks had lower algal cover compared with all other treatments. We hypothesize this effect is caused by higher densities and grazing intensities of herbivorous macroinvertebrates on those sorts of substrata, analogous to findings for marine habitats. Abrasion does not kill A. hermannii, whereas overturning likely does, necessitating new colonization. Floods often create a mix of abrasion and overturning, producing a mosaic of patches, the complexity of which is not represented well by measures of average disturbance intensity over a whole site. The use of the latter may explain some recent contradictory results among stream disturbance studies. A patch‐level perspective is needed when disturbance creates mosaics over the landscape.     

Does variation in patch use among butterfly species contribute to nestedness at fine spatial scales?

A nested pattern occurs whenever the species observed in depauperate habitat patches are a subset of those found in more species‐rich patches. Ecologists have documented many instances of nestedness caused by population‐level processes such as colonization and extinction at biogeographic scales. However, few researchers have examined whether nestedness may exist at fine scales due to the ways in which individual organisms discriminate among potential habitat patches. In 1999, we experimentally fragmented an old‐field habitat into patches of varying size to test whether nestedness could exist on a fine spatial scale. Five treatments of differing patch size were replicated five times in a Latin square design by selectively mowing 15×15 m² plots within an old‐field (patch areas: 225, 180, 135, 90, and 45 m²). Specifically, we tested whether butterflies foraging within a network of patches differing in area conformed to a nested subset structure. We also classified species according to (1) their flight height while foraging (high or low), and (2) their adult habitat breadth (ubiquitous, general, or restricted) to determine whether nestedness could be explained by difference in species’ tendency to discriminate among patches differing in area.
We found significant evidence that a community of foraging Lepidoptera conformed to a nested subset structure based on the difference between the observed nestedness within the butterfly community and the nestedness obtained from randomly generated species presence/absence matrices. Poisson regression analyses demonstrated that high‐flying, habitat‐restricted species avoided the smallest patches (90 and 45 m²) in favor of larger remnants, whereas low‐flying, habitat generalists used all patch sizes. Thus, our study is one of the first to demonstrate that nestedness among species subsets can be observed at fine spatial scales (within a single 1.5 hectare field) and may be maintained by species behavioral differences: discriminating species (i.e. high‐flying, habitat restricted) avoided the smallest patches, and less discriminating species (i.e. low‐flying, ubiquitous) were distributed throughout the field without regard to patch size. Our results also suggest that nestedness should be viewed as yet another scalar pattern in ecology, generated by variation in patch use by individuals at fine‐scales as well as the more traditionally invoked processes of extinction and colonization of species at broad‐scales.     

Habitat�Cperformance relationships: finding the right metric at a given spatial scale

The field of habitat ecology has been muddled by imprecise terminology regarding what constitutes habitat, and how importance is measured through use, selection, avoidance and other bio-statistical terminology. Added to the confusion is the idea that habitat is scale-specific. Despite these conceptual difficulties, ecologists have made advances in understanding ‘how habitats are important to animals’, and data from animal-borne global positioning system (GPS) units have the potential to help this clarification. Here, we propose a new conceptual framework to connect habitats with measures of animal performance itself—towards assessing habitat–performance relationship (HPR). Long-term studies will be needed to estimate consequences of habitat selection for animal performance. GPS data from wildlife can provide new approaches for studying useful correlates of performance that we review. Recent examples include merging traditional resource selection studies with information about resources used at different critical life-history events (e.g. nesting, calving, migration), uncovering habitats that facilitate movement or foraging and, ultimately, comparing resources used through different life-history strategies with those resulting in death. By integrating data from GPS receivers with other animal-borne technologies and combining those data with additional life-history information, we believe understanding the drivers of HPRs will inform animal ecology and improve conservation.     

Effects of spatial scale and sample size in GPS-based species distribution models: are the best models trivial for red deer management?

Species distribution models (SDMs) are popular in conservation and management of a wide array of taxa. Often parameterized with coarse GIS-based environmental maps, they perform well in macro-ecological settings but it is debated if the models can predict distribution within broadly suitable “known” habitats of interest to local managers. We parameterized SDMs with GIS-derived environmental variables and location data from 82 GPS-collared female red deer (Cervus elaphus) from two study areas in Norway. Candidate GLM models were fitted to address the effect of spatial scale (landscape vs. home range), sample size, and transferability between study areas, with respect to predictability (AUC) and explained variance (Generalized R ² and deviance). The landscape level SDM captured variation in deer distribution well and performed best on all diagnostic measures of model quality, caused mainly by a trivial effect of avoidance of non-habitat (barren mountains). The home range level SDMs were far less predictable and explained comparatively little variation in space use. Landscape scale models stabilized at the low sample size of 5–10 individuals and were highly transferrable between study areas implying a low degree of individual variation in habitat selection at this scale. It is important to have realistic expectations of SDMs derived from digital elevation models and coarse habitat maps. They do perform well in highlighting potential habitat on a landscape scale, but often miss nuances necessary to predict more fine-scaled distribution of wildlife populations. Currently, there seems to be a trade-off between model quality and usefulness in local management.     

Clumped versus scattered: how does the spatial correlation of disturbance events affect biodiversity?

In this study, we systematically explore the effects of rate and spatial correlation (level of clumping) of disturbance events on a community of sessile species differing in their life history traits. A spatially explicit individual-based model shows that long-term coexistence is very sensitive to spatial correlation when the trade-off in life history traits includes differences in dispersal distances. Highest biodiversity emerges at highly correlated disturbances of intermediate rates. Diversity peaks shift to larger rates when clumping decreases. Scattered disturbances lead to competitive exclusion. Interestingly, we observed additional peaks in the diversity–disturbance curves at certain levels of clumping. Thus, subject to the differences in life history traits, particular combinations of disturbance rate and spatial correlation may enable subsets of species to coexist, which opens new possibilities for explaining diversity. Our results suggest that observation of high biodiversity under spatially correlated disturbances points to a competition–colonisation trade-off, which includes dispersal distances.     

Are raccoons limited by the availability of breeding resources? Evidence of variability in fecundity at fine spatial scales

Despite their behavioral plasticity, recent research suggests raccoons (Procyon lotor) exhibit variability in demography and genetic structure among individual habitat patches in landscapes heavily affected by anthropogenic land use. Consequently, elucidation of vital rates at fine-spatial scales is needed to implement appropriate management strategies for this species. To evaluate the degree of variability in productivity that exists among individual habitat patches, we collected reproductive (n = 170) and cementum annuli age data (n = 383) for raccoons occupying 30 forest patches varying in local and landscape-level habitat attributes within a highly fragmented agricultural ecosystem. Across all females sampled, pregnancy rates averaged 85% but were highly variable among ages (range: 47–100%). Average litter sizes ranged from 3.2 to 4.7, but did not differ as a function of age. At the landscape-level, we observed significant variability among habitat patches in the total number of offspring produced (range: 0–80), indicating that individual patches vary in their contribution to the overall size and stability of the global (landscape-level) population. Variability in productivity among habitat patches primarily was driven by local differences in the availability of denning resources, likely because of the influence of this variable on variability in the number, age structure, and reproductive rate of females. Our results suggest that in agricultural ecosystems, the reproductive potential and temporal stability of raccoons within individual habitat fragments is inextricably linked to the density of tree cavities. © 2012 The Wildlife Society.     

How does oak mast seeding affect the feeding behavior of sympatric red and roe deer?

Oak reproduction is characterized by mast seeding with high inter-annual fluctuations in fruit production. Such resource pulses can greatly affect ecosystem functioning and may cause seed consumers to alter their mobility, demography, or diet. Consequences of mast seeding for seed consumers remain poorly understood as their long timescale makes them difficult to study. We investigated impacts of oak mast seeding on the feeding behavior of two sympatric European deer species: red deer (Cervus elaphus) and roe deer (Capreolus capreolus). We analyzed their rumen content over a 31-year period in tandem with 10 years of data on oak fructification (i.e. 8 years of field monitoring and two modelled years). Acorn production is strongly correlated with consumption by both deer species. In years of high fructification, acorns represent more than 50% and 35% of red and roe deer diet, respectively, confirming assumptions that deer favor acorns when these are available. Red deer eat more acorns than roe deer both between and within years. High acorn production in mast years appears to saturate the capacity of deer to consume acorns. As the proportion of acorns increase in their diet, red deer eat more grasses and less conifer browse. No dietary shift was found for roe deer. By inducing dietary shifts in consumers, oak mast seeding can have cascading effects on ecosystem processes, notably on the damages on conifers caused by red deer and the consequences for forest dynamics.     

How can Habitat Selection Affect the use of a Wetland Complex by Waterbirds?

The factors regulating the distribution of dabbling and diving waterbirds were studied, taking into account habitat selection by the species in a wetland complex of 26 ponds in south-eastern Spain. Such information can be used to management and conservation of wetland threatened bird species. Direct counts and feeding-microhabitat surveys of waterbirds were conducted. The feeding-niche width and the feeding-microhabitat use, as a function of the horizontal spatial gradient in the ponds, were related to the mean size of ponds used for each species. While the more generalist birds, which usually feed close to the shore, probably had available resources in small ponds, specialists that also frequently selected central zones of the pond had proportionally more limited feeding space and, therefore, less resource availability in small ponds. The differences in habitat selection of the different species appeared to encourage their hierarchical disappearance from the wetland complex at the same rate as the ponds diminished in size (‘nested’ pattern). The results support the conservation, restoration or creation of, at least, ponds of greater size in order to preserve extensive open-water zones in the wetlands and maintain the greatest number of specialist, threatened, and area-dependent species, such as the globally endangered White-headed Duck (Oxyura leucocephala).     

Earlier breeding,lower success: does the spatial scale of climatic conditions matter in a migratory passerine bird?

Following over 20 years of research on the climatic effects on biodiversity we now have strong evidence that climate change affects phenology, fitness, and distribution ranges of different taxa, including birds. Bird phenology likely responds to changes in local weather. It is also affected by climatic year‐to‐year variations on larger scales. Although such scale‐related effects are common in ecology, most studies analyzing the effects of climate change were accomplished using climatic information on a single spatial scale. In this study, we aimed at determining the scale‐dependent sensitivity of breeding phenology and success to climate change in a migratory passerine bird, the barn swallow (Hirundo rustica). For both annual broods, we investigated effects of local weather (local scale) and the North Atlantic Oscillation (NAO, large scale) on the timing of breeding and breeding success. Consistent with previous studies in migratory birds we found that barn swallows in Eastern Germany bred progressively earlier. At the same time, they showed reduced breeding success over time in response to recent climatic changes. Responses to climatic variation were observed on both local and large climatic scales, but they differed with respect to the ecological process considered. Specifically, we found that the timing of breeding was primarily influenced by large‐scale NAO variations and to a lesser extent by local weather on the breeding grounds. Conversely, climatic conditions on the local scale affected breeding success, exclusively. The observed decrease in breeding success over years is likely a consequence of scale‐related mismatches between climatic conditions during different breeding phases. This provides further evidence that a species' response of earlier breeding may not be enough to cope with climate change. Our results emphasize the importance of considering the response of ecological processes along different climatic scales in order to better understand the complexity of climate change effects on biodiversity.     

Host-parasite interactions between the local and the mean-field: how and when does spatial population structure matter?

The assumption that populations are completely mixed is reasonable for many populations, but there is likely to be some degree of local interaction whether spatially or socially in many systems. An important question is therefore how strong these local interactions need to be before there are significant effects on the dynamics of the system. Here, our approach is to use a multi-scale pair-approximation model to move between completely local and completely mixed host-parasite interactions. We show that systems dominated by near neighbour effects have less persistence of disease, and a greater possibility of parasite driven extinction and limit cycles. Furthermore this reduction in persistence occurs over a wide range of infection scales and is still significant in predominantly mixed host populations. Deterministic extinctions are only likely in highly spatial SI systems while oscillations also persist over a wide range of infection ranges, but only in hosts that reproduce mostly locally. In general the mean-field may well be a good approximation for many systems, even when there are a significant proportion of near neighbour events, but this depends crucially on the ecological context.     

Operationalisation and application of water supply mix (WSmix) at worldwide scale: how does WSmix influence the environmental profile of water supply for different users?

The International Journal of Life Cycle Assessment - A worldwide-regionalized water supply mix (WSmix) has been developed for use in life cycle assessment (LCA) studies. The WSmix is the...     

Patterns of size variation in bees at a continental scale: does Bergmann's rule apply?

Body size latitudinal clines have been widley explained by the Bergmann's rule in homeothermic vertebrates. However, there is no general consensus in poikilotherms organisms in particular in insects that represent the large majority of wildlife. Among them, bees are a highly diverse pollinators group with high economic and ecological value. Nevertheless, no comprehensive studies of species assemblages at a phylogenetically larger scale have been carried out even if they could identify the traits and the ecological conditions that generate different patterns of latitudinal size variation. We aimed to test Bergmann's rule for wild bees by assessing relationships between body size and latitude at continental and community levels. We tested our hypotheses for bees showing different life history traits (i.e. sociality and nesting behaviour). We used 142 008 distribution records of 615 bee species at 50 × 50 km (CGRS) grids across the West Palearctic. We then applied generalized least squares fitted linear model (GLS) to assess the relationship between latitude and mean body size of bees, taking into account spatial autocorrelation. For all bee species grouped, mean body size increased with higher latitudes, and so followed Bergmann's rule. However, considering bee genera separately, four genera were consistent with Bergmann's rule, while three showed a converse trend, and three showed no significant cline. All life history traits used here (i.e. solitary, social and parasitic behaviour; ground and stem nesting behaviour) displayed a Bergmann's cline. In general there is a main trend for larger bees in colder habitats, which is likely to be related to their thermoregulatory abilities and partial endothermy, even if a ‘season length effect’ (i.e. shorter foraging season) is a potential driver of the converse Bergmann's cline particularly in bumblebees.     

Revealing unexpected uses of space by wintering Aquila pomarina: how does satellite telemetry identify behaviour at different scales?

Little is understood about the dispersion and movements of Palaearctic migrant raptors while wintering in southern Africa. The high temporal and spatial resolution of GPS telemetry data provided the opportunity to describe how space is used by one such migratory raptor in its wintering range, the lesser spotted eagle Aquila pomarina. Kernel density estimation was used to map the distribution of three individuals at various spatial scales. In addition to their extremely large overall wintering range (up to 112 000 km²), three finer levels of spatial concentration were identified: favoured activity zones where the birds spent much of the winter, smaller core areas to which the birds returned each year, and tiny intensive foraging clusters. Philopatry was demonstrated by one bird which revisited core areas over eight wintering seasons. The same core areas, particularly the Waterberg, Grootfontein (Namibia) and the eastern and western sides of the Okavango Delta (Botswana), were visited by two other eagles in 2012/2013, although not simultaneously. Such results potentially provide important information on areas where conservation activities might be focused to mitigate human degradation of habitat.     

Variance partitioning of deconstructed periphyton communities: does the use of biological traits matter?

The use of species traits offers a promising approach to the understanding of the main processes underlying metacommunity patterns. We analyzed samples of periphytic algae in 30 environments of the Upper Paraná River floodplain in southeastern Brazil, to test the hypotheses that variation in species composition of algal groups with low dispersal abilities would be mainly explained by spatial variables; on the other hand, algal groups with higher dispersal abilities would be better explained by environmental variables. The variation in community structure was mainly correlated with environmental variables. This result is in line with a growing body of evidence indicating a predominant role of species-sorting processes. The more-refined prediction that the spatial variables would gradually become more important across a gradient of adherence or size was, however, not supported by our analyses. Also, the large unexplained variation suggested that these periphytic communities were assembled by idiosyncratic events, or that other variables that are often neglected in studies of aquatic metacommunities needed to be included.     

Rapid recolonisation by the European red fox: how effective are uncoordinated and isolated control programs?

Uncoordinated and isolated control programs are often used by land managers, property owners and recreational hunters to control numbers and reduce the impacts of European red foxes (Vulpes vulpes). However, decades of such attempts to eradicate this significant agricultural and biodiversity pest in many countries have failed. We investigated the effectiveness of an uncoordinated and isolated shooting program to determine if it caused any change in red fox population density. We also determined whether shooting is more cost effective than poison baiting for fox control. First, we estimated the density of foxes on an agricultural study property using distance sampling and rates of bait uptake before and after a control program. Second, we estimated the costs associated with undertaking the control program and compared it to the estimated costs of undertaking poison baiting. Prior to control, we estimated a density of 4.18 foxes per square kilometre. After the control exercise, which removed 47 individuals in 12 nights, we estimated a density of 3.26 foxes per square kilometre. Our results provide evidence that one-off control programs are not effective in greatly reducing red fox density, even if the control effort is intensive. Where large-scale control programs cannot be coordinated, isolated programs should therefore involve follow-up campaigns to reduce population recovery. On a local scale, combinations of shooting and baiting may also provide maximum control impact at minimal cost.     

Geographical separation of two Ulex species at three spatial scales: does competition limit species' ranges?

It is a common assumption that species' ranges are limited by their physiological tolerances to climatic factors, Biotic factors, such as competition, are rarely considered. We investigated the distributions of Ulex minor and U. gallii at three spatial scales from geographic ranges to individual heaths - to examine whether the species are negatively associated, as predicted by the hypothesis that the ranges of the species are limited by competition with each other. Distribution maps for the British Isles and France (100 400 km² survey units) show the two species have largely separated, but slightly overlapping ranges. A region of range overlap on the heaths of Dorset, southern England was mapped using 4 ha survey squares. There was strong negative association between the species, and the heaths could be divided into zones where one species was dominant. There was some indication of edaphic differences between the U. minor -dominated zones and the U. gallii zones. The few heaths where the species co-occurred were surveyed using 4 m² quadrats placed along transects. Usually one species was widespread over the heath, while the other occurred in patches. The species were strongly negatively associated in all transects. Therefore, the two species showed strong negative associations at three mapping scales. Apparent co-occurrences detected at one spatial scale largely disappeared when species were mapped at finer scales, emphasising the fractal nature of distributions. This provides evidence that the distributions of the two species are not independent and that they cannot coexist, and therefore that their ranges are limited by competition. Over their ranges, competitive superiority is probably determined by the climate. At the range boundaries in the region of overlap, climate is not important, but other physical factors such as edaphic conditions may determine the outcome of competition.