Dispersal connectivity and reserve selection for marine conservation

Although larval dispersal is crucial for the persistence of most marine populations, dispersal connectivity between sites is rarely considered in designing marine protected area networks. In particular the role of structural characteristics (known as topology) for the network of larval dispersal routes in the conservation of metapopulations has not been addressed. To determine reserve site configurations that provide highest persistence values with respect to their connectivity characteristics, we model nine connectivity topological models derived from graph theory in a demographic metapopulation model. We identify reserve site configurations that provide the highest persistence values for each of the metapopulation connectivity models. Except for the minimally connected and fully connected populations, we observed two general ‘rules of thumb’ for optimising the mean life time for all topological models: firstly place the majority of reserves, so that they are neighbours of each other, on the sites where the number of connections between the populations is highest (hub), secondly when the reserves have occupied the majority of the vertices in the hub, then select another area of high connectivity and repeat. If there are no suitable hubs remaining then distribute the remaining reserves to isolated locations optimising contact with non-reserved sites.     

Marine reserve design: optimal size, habitats, species affinities, diversity, and ocean microclimate.

The design of marine reserves is complex and fraught with uncertainty. However, protection of critical habitat is of paramount importance for reserve design. We present a case study as an example of a reserve design based on fine-scale habitats, the affinities of exploited species to these habitats, adult mobility, and the physical forcing affecting the dynamics of the habitats. These factors and their interaction are integrated in an algorithm that determines the optimal size and location of a marine reserve for a set of 20 exploited species within five different habitats inside a large kelp forest in southern California. The result is a reserve that encompasses approximately 42% of the kelp forest. Our approach differs fundamentally from many other marine reserve siting methods in which goals of area, diversity, or biomass are targeted a priori. Rather, our method was developed to determine how large a reserve must be within a specific area to protect a self-sustaining assemblage of exploited species. The algorithm is applicable across different ecosystems, spatial scales, and for any number of species. The result is a reserve in which habitat value is optimized for a predetermined set of exploited species against the area left open to exploitation. The importance of fine-scale habitat definitions for the exploited species off La Jolla is exemplified by the spatial pattern of habitats and the stability of these habitats within the kelp forest, both of which appear to be determined by ocean microclimate.     

Ornaments and condition: plumage patch sizes,nutritional reserve state,reserve accumulation,and reserve depletion

Behavioral Ecology and Sociobiology - Cooperation plays a crucial role in primate social life. However, the evolution of large-scale human cooperation from the cognitive fundamentals found in other...     

Finding all optimal solutions to the reserve site selection problem: formulation and computational analysis

The problem of selecting nature reserves has received increased attention in the literature during the past decade, and a variety of approaches have been promoted for selecting those sites to include in a reserve network. One set of techniques employs heuristic algorithms and thus provides possibly sub-optimal solutions. Another set of models and accompanying algorithms uses an integer programming formulation of the problem, resulting in an optimization problem known as the Maximal Covering Problem, or MCP. Solution of the MCP provides an optimal solution to the reserve site selection problem, and while various algorithms can be employed for solving the MCP they all suffer from the disadvantage of providing a single optimal solution dictating the selection of areas for conservation. In order to provide complete information to decision makers, the determination of all alternate optimal solutions is necessary. This paper explores two procedures for finding all such solutions. We describe the formulation and motivation of each method. A computational analysis on a data set describing native terrestrial vertebrates in the state of Oregon illustrates the effectiveness of each approach.     

Using circuit theory to model connectivity in ecology, evolution, and conservation

Connectivity among populations and habitats is important for a wide range of ecological processes. Understanding, preserving, and restoring connectivity in complex landscapes requires connectivity models and metrics that are reliable, efficient, and process based. We introduce a new class of ecological connectivity models based in electrical circuit theory. Although they have been applied in other disciplines, circuit-theoretic connectivity models are new to ecology. They offer distinct advantages over common analytic connectivity models, including a theoretical basis in random walk theory and an ability to evaluate contributions of multiple dispersal pathways. Resistance, current, and voltage calculated across graphs or raster grids can be related to ecological processes (such as individual movement and gene flow) that occur across large population networks or landscapes. Efficient algorithms can quickly solve networks with millions of nodes, or landscapes with millions of raster cells. Here we review basic circuit theory, discuss relationships between circuit and random walk theories, and describe applications in ecology, evolution, and conservation. We provide examples of how circuit models can be used to predict movement patterns and fates of random walkers in complex landscapes and to identify important habitat patches and movement corridors for conservation planning.     

Epiphyte metapopulation dynamics are explained by species traits, connectivity, and patch dynamics

The colonization-extinction dynamics of many species are affected by the dynamics of their patches. For increasing our understanding of the metapopulation dynamics of sessile species confined to dynamic patches, we fitted a Bayesian incidence function model extended for dynamic landscapes to snapshot data on five epiphytic lichens among 2083 mapped oaks (dynamic patches). We estimate the age at which trees become suitable patches for different species, which defines their niche breadth (number of suitable trees). We show that the colonization rates were generally low, but increased with increasing connectivity in accordance with metapopulation theory. The rates were related to species traits, and we show, for the first time, that they are higher for species with wide niches and small dispersal propagules than for species with narrow niches or large propagules. We also show frequent long-distance dispersal in epiphytes by quantifying the relative importance of local dispersal and background deposition of dispersal propagules. Local stochastic extinctions from intact trees were negligible in all study species, and thus, the extinction rate is set by the rate of patch destruction (tree fall). These findings mean that epiphyte metapopulations may have slow colonization-extinction dynamics that are explained by connectivity, species traits, and patch dynamics.     

Uncertainty, learning, and the optimal management of wildlife

Wildlife management is limited by uncontrolled and often unrecognized environmental variation, by limited capabilities to observe and control animal populations, and by a lack of understanding about the biological processes driving population dynamics. In this paper I describe a comprehensive framework for management that includes multiple models and likelihood values to account for structural uncertainty, along with stochastic factors to account for environmental variation, random sampling, and partial controllability. Adaptive optimization is developed in terms of the optimal control of incompletely understood populations, with the expected value of perfect information measuring the potential for improving control through learning. The framework for optimal adaptive control is generalized by including partial observability and non-adaptive, sample-based updating of model likelihoods. Passive adaptive management is derived as a special case of constrained adaptive optimization, representing a potentially efficient suboptimal alternative that nonetheless accounts for structural uncertainty.     

Urban growth and landscape connectivity threats assessment at Saguaro National Park,Arizona, USA

Urban and exurban expansion results in habitat and biodiversity loss globally. We hypothesize that a coupled-model approach could connect urban planning for future cities with landscape ecology to consider wildland habitat connectivity. Our work combines urban growth simulations with models of wildlife corridors to examine how species will be impacted by development to test this hypothesis. We leverage a land use change model (SLEUTH) with structural and functional landscape-connectivity modeling techniques to ascertain the spatial extent and locations of connectivity related threats to a national park in southern Arizona, USA, and describe how protected areas might be impacted by urban expansion. Results of projected growth significantly altered structural connectivity (80%) when compared to current (baseline) corridor conditions. Moreover, projected growth impacted functional connectivity differently amongst species, indicating resilience of some species and near-complete displacement of others. We propose that implementing a geospatial-design-based model will allow for a better understanding of the impacts management decisions have on wildlife populations. The application provides the potential to understand both human and environmental impacts of land-system dynamics, critical for long-term sustainability.     

Mosquito biodiversity of Dibru-Saikhowa biosphere reserve in Assam, India

Entomological surveys were conducted for three consecutive years in core and buffer zone of the Dibru-Saikhowa biosphere reserve in pre monsoon, monsoon and post-monsoon seasons. A total of 52 species of mosquitoes under eleven genera have been detected. The genus Anopheles (18 species) was the predominant followed by Culex, Aedes, Mansonia, Armigeres, Mimomyia, Ochlerostatus, Malaya, Toxorhynchites, Ficalbia and Aedeomyia. The buffer zone of the forest reserve where human habitations are there exhibited the presence of maximum number of species (49 species under 10 genera) in comparison to core zone (42 species under 10 genera). In buffer zone, maximum numbers of species (38) were recorded in monsoon season followed by post- monsoon (35 species) and Pre-monsoon season (34 species). Whereas in core zone, maximum number of species were collected in post monsoon season followed by pre monsoon season and monsoon season. In Core and buffer zone, the maximum species were recorded from the ground pool habitat and slow flowing stream respectively. Among the disease vectors, the potential Japanese encephalitis vectors incriminated in India were very much prevalent. This study provides the list of available mosquito species recorded for the first time in the Dibru-Saikhowa biosphere reserve.     

Edge effects, not connectivity, determine the incidence and development of a foliar fungal plant disease

Using a model plant-pathogen system in a large-scale habitat corridor experiment, we found that corridors do not facilitate the movement of wind-dispersed plant pathogens, that connectivity of patches does not enhance levels of foliar fungal plant disease, and that edge effects are the key drivers of plant disease dynamics. Increased spread of infectious disease is often cited as a potential negative effect of habitat corridors used in conservation, but the impacts of corridors on pathogen movement have never been tested empirically. Using sweet corn (Zea mays) and southern corn leaf blight (Cochliobolus heterostrophus) as a model plant-pathogen system, we tested the impacts of connectivity and habitat fragmentation on pathogen movement and disease development at the Savannah River Site, South Carolina, USA. Over time, less edgy patches had higher proportions of diseased plants, and distance of host plants to habitat edges was the greatest determinant of disease development. Variation in average daytime temperatures provided a possible mechanism for these disease patterns. Our results show that worries over the potentially harmful effects of conservation corridors on disease dynamics are misplaced, and that, in a conservation context, many diseases can be better managed by mitigating edge effects.     

Corridors promote fire via connectivity and edge effects

Landscape corridors, strips of habitat that connect otherwise isolated habitat patches, are commonly employed during management of fragmented landscapes. To date, most reported effects of corridors have been positive; however, there are long-standing concerns that corridors may have unintended consequences. Here, we address concerns over whether corridors promote propagation of disturbances such as fire. We collected data during prescribed fires in the world's largest and best replicated corridor experiment (Savannah River Site, South Carolina, USA), six -50-ha landscapes of open (shrubby/herbaceous) habitat within a pine plantation matrix, to test several mechanisms for how corridors might influence fire. Corridors altered patterns of fire temperature through a direct connectivity effect and an indirect edge effect. The connectivity effect was independent of fuel levels and was consistent with a hypothesized wind-driven "bellows effect." Edges, a consequence of corridor implementation, elevated leaf litter (fuel) input from matrix pine trees, which in turn increased fire temperatures. We found no evidence for corridors or edges impacting patterns of fire spread: plots across all landscape positions burned with similar probability. Impacts of edges and connectivity on fire temperature led to changes in vegetation: hotter-burning plots supported higher bunch grass cover during the field season after burning, suggesting implications for woody/herbaceous species coexistence. To our knowledge, this represents the first experimental evidence that corridors can modify landscape-scale patterns of fire intensity. Corridor impacts on fire should be carefully considered during landscape management, both in the context of how corridors connect or break distributions of fuels and the desired role of fire as a disturbance, which may range from a management tool to an agent to be suppressed. In our focal ecosystem, longleaf pine woodland, corridors might provide a previously unrecognized benefit during prescribed burning activities, by promoting fire intensity, which may assist in promoting plant biodiversity.     

Dispersal ecology of deadwood organisms and connectivity conservation

Limited knowledge of dispersal for most organisms hampers effective connectivity conservation in fragmented landscapes. In forest ecosystems, deadwood‐dependent organisms (i.e., saproxylics) are negatively affected by forest management and degradation globally. We reviewed empirically established dispersal ecology of saproxylic insects and fungi. We focused on direct studies (e.g., mark‐recapture, radiotelemetry), field experiments, and population genetic analyses. We found 2 somewhat opposite results. Based on direct methods and experiments, dispersal is limited to within a few kilometers, whereas genetic studies showed little genetic structure over tens of kilometers, which indicates long‐distance dispersal. The extent of direct dispersal studies and field experiments was small and thus these studies could not have detected long‐distance dispersal. Particularly for fungi, more studies at management‐relevant scales (1–10 km) are needed. Genetic researchers used outdated markers, investigated few loci, and faced the inherent difficulties of inferring dispersal from genetic population structure. Although there were systematic and species‐specific differences in dispersal ability (fungi are better dispersers than insects), it seems that for both groups colonization and establishment, not dispersal per se, are limiting their occurrence at management‐relevant scales. Because most studies were on forest landscapes in Europe, particularly the boreal region, more data are needed from nonforested landscapes in which fragmentation effects are likely to be more pronounced. Given the potential for long‐distance dispersal and the logical necessity of habitat area being a more fundamental landscape attribute than the spatial arrangement of habitat patches (i.e., connectivity sensu strict), retaining high‐quality deadwood habitat is more important for saproxylic insects and fungi than explicit connectivity conservation in many cases.     

Sex ratio and optimal harvest of canvasback ducks,A model

The North American population of canvasback ducks (Aythya valisineria) exhibits extreme distortion of the sex ratio in favor of males. This paper describes a model which accounts for this pattern by relatively heavier female mortality in both the breeding and nonbreeding seasons. The density-dependence of winter mortality leads to the conclusion that the observed sex ratio depresses total population numbers. Variation in nesting success is shown to influence sex ratios and strongly depress population numbers. Because a standard harvest scheme can be demonstrated to severely depress the numbers of ducks, an alternative graduated or weighted harvest procedure is recommended.     

Influence of habitat quality, population size, patch size, and connectivity on patch-occupancy dynamics of the middle spotted woodpecker

Despite extensive research on the effects of habitat fragmentation, the ecological mechanisms underlying colonization and extinction processes are poorly known, but knowledge of these mechanisms is essential to understanding the distribution and persistence of populations in fragmented habitats. We examined these mechanisms through multiseason occupancy models that elucidated patch-occupancy dynamics of Middle Spotted Woodpeckers (Dendrocopos medius) in northwestern Spain. The number of occupied patches was relatively stable from 2000 to 2010 (15-24% of 101 patches occupied every year) because extinction was balanced by recolonization. Larger and higher quality patches (i.e., higher density of oaks >37 cm dbh [diameter at breast height]) were more likely to be occupied. Habitat quality (i.e., density of large oaks) explained more variation in patch colonization and extinction than did patch size and connectivity, which were both weakly associated with probabilities of turnover. Patches of higher quality were more likely to be colonized than patches of lower quality. Populations in high-quality patches were less likely to become extinct. In addition, extinction in a patch was strongly associated with local population size but not with patch size, which means the latter may not be a good surrogate of population size in assessments of extinction probability. Our results suggest that habitat quality may be a primary driver of patch-occupancy dynamics and may increase the accuracy of models of population survival. We encourage comparisons of competing models that assess occupancy, colonization, and extinction probabilities in a single analytical framework (e.g., dynamic occupancy models) so as to shed light on the association of habitat quality and patch geometry with colonization and extinction processes in different settings and species.     

Behaviour that influences dispersal and connectivity in the small,young larvae of a reef fish

Determining the scale of larval dispersal and population connectivity in demersal fishes is a major challenge in marine ecology. Historically, considerations of larval dispersal have ignored the possible contributions of larval behaviour, but we show here that even young, small larvae have swimming, orientation and vertical positioning capabilities that can strongly influence dispersal outcomes. Using young (11–15 days), relatively poorly developed (8–10 mm), larvae of the pomacentrid damselfish, Amblyglyphidodon curacao (identified using mitochondrial DNA), we studied behaviour relevant to dispersal in the laboratory and sea on windward and leeward sides of Lizard Island, Great Barrier Reef. Behaviour varied little with size over the narrow size range examined. Critical speed was 27.5 ± 1.0 cm s⁻¹ (30.9 BL s⁻¹), and in situ speed was 13.6 ± 0.6 cm s⁻¹. Fastest individuals were 44.6 and 25.0 cm s⁻¹, for critical and in situ speeds, respectively. In situ speed was about 50% of critical speed and equalled mean current speed. Unfed larvae swam 172 ± 29 h at 8–10 cm s⁻¹ (52.0 ± 8.6 km), and lost 25% wet weight over that time. Vertical distribution differed between locations: modal depth was 2.5–5.0 and 10.0–12.5 m at leeward and windward sites, respectively. Over 80% of 71 larvae observed in situ had directional swimming trajectories. Larvae avoided NW bearings, with an overall mean SE swimming direction, regardless of the direction to nearest settlement habitat. Larvae made smaller changes between sequential bearings of swimming direction when swimming SE than in other directions, making it more likely they would continue to swim SE. When swimming NW, 62% of turns were left (more than in other directions), which would quickly result in swimming direction changing away from NW. This demonstrates the larvae knew the direction in which they were swimming and provides insight into how they achieved SE swimming direction. Although the cues used for orientation are unclear, some possibilities seemingly can be eliminated. Thus, A. curacao larvae near Lizard Island, on average swam into the average current at a speed equivalent to it, could do this for many hours, and chose different depths in different locations. These behaviours will strongly influence dispersal, and are similar to behaviour of other settlement-stage pomacentrid larvae that are older and larger.     

Ecological and social determinants of spacing behaviour in desert baboon groups

This paper investigates the determinants of individual spacing behaviour in a desert baboon population (Papio cynocephalus ursinus). Patterns of neighbour proximity and neighbour density were examined among adults in four groups under different ecological and social conditions (through instantaneous sampling during focal follows). Initial analysis of these data shows that (1) the use of vertical substrates (refuges such as tall trees and cliff faces) can confound patterns of spacing, and (2) individual differences in spacing can depend on the spatial scale over which it is measured. To minimise these substrate and scale effects, this analysis focuses on animals which are off refuges and examines spacing behaviour through its underlying statistical `dimensions' (identified through factor analysis). Analysis of these dimensions indicates that sex, group size, activity-habitat and female reproductive state can all have independent effects on spacing: (1) males are more dispersed than females in smaller groups, (2) male and female dispersion increases with time spent in foraging habitats, and (3) female dispersion is reduced during lactation. According to the hypotheses tested, these results indicate that feeding competition only affects spacing behaviour during foraging while predation risk plays little or no role in spacing. Most aspects of spacing behaviour are best explained by male reproductive strategies and their social repercussions. Received: 25 May 1998 / Accepted after revision: 18 July 1998     

Catastrophe management and inter-reserve distance for marine reserve networks

We consider the optimal spacing between marine reserves for maximising the viability of a species occupying a reserve network. The closer the networks are placed together, the higher the probability of colonisation of an empty reserve by an occupied reserve, thus increasing population viability. However, the closer the networks are placed together, the higher the probability that a catastrophe will cause extinction of the species in both reserves, thus decreasing population viability. Using a simple discrete-time Markov chain model for the presence or absence of the species in each reserve we determine the distance between the two reserves which provides the optimal trade-off between these processes, resulting in maximum viability of the species.