Habitat selection, interspecific interactions and landscape composition (original) (raw)
Related papers
Effects of Habitat Loss and Fragmentation on Population Dynamics
Conservation Biology, 2005
We used a spatially explicit population model that was generalized to produce nine ecological profiles of long-lived species with stable home ranges and natal dispersal to investigate the effects of habitat loss and fragmentation on population dynamics. We simulated population dynamics in landscapes composed of three habitat types (good-quality habitat ranging from 10-25%, poor-quality habitat ranging from 10-70%, and matrix). Landscape structures varied from highly fragmented to completely contiguous. The specific aims of our model were (1) to investigate under which biological circumstances the traditional approach of using two types only (habitat and matrix) failed and assess the potential impact of restoring matrix to poorquality habitat, (2) to investigate how much of the variation in population size was explained by landscape composition alone and which key attributes of landscape structure can serve as predictors of population response, and (3) to estimate the maximum fragmentation effects expressed in equivalent pure loss of goodquality habitat. Poor-quality habitat mattered most in situations when it was generally not considered (i.e., for metapopulations or spatially structured populations when it provides dispersal habitat). Population size increased up to 3 times after restoring matrix to poor-quality habitat. Overall, habitat amount accounted for 68% of the variation in population size, whereas ecological profile and fragmentation accounted for approximately 13% each. The maximal effect of (good-quality) habitat fragmentation was equivalent to a pure loss of up to 15% of good-quality habitat, and the maximal loss of individuals resulting from maximal fragmentation reached 80%. Abundant dispersal habitat and sufficiently large dispersal potential, however, resulted in functionally connected landscapes, and maximal fragmentation had no effect at all. Our findings suggest that predicting fragmentation effects requires a good understanding of the biology and habitat use of the species in question and that the uniqueness of species and the landscapes in which they live confound simple analysis.
Source–Sink Dynamics and the Coexistence of Species on a Single Resource
Theoretical Population Biology, 1997
We investigate the potential for coexistence of species that compete for a shared resource when the resource occurs in both a source area acting as a refuge and a sink area where it is used by the competing species. Our model shows that the mixing rate between the source and sink resource populations has a dramatic influence on the outcome of competition. When there is a strict sink source dependence, so that resource renewal in the sink is entirely dependent on the source, only exploitation competition decides which species can survive at a very small mixing rate. Increasing the flow rate basically amounts to increasing the role played by interference competition. If interspecific interference is very small, compared with intraspecific interference, increasing the mixing rate allows coexistence of many species, indeed, unlimited coexistence if the species' resource exploitation efficiencies are similar enough. If interspecific interference is significant and there is a trade-off between the exploitation and interference competitive abilities of two species, it is possible to have one species replacing the other along a gradient of increasing mixing rate, with either coexistence or alternative single-species equilibria at intermediate values of the mixing rate. It is also possible to have one species always outcompeting the other, or alternative single-species stable equilibria at large mixing rates. When the strict sink source dependence is relaxed by allowing the resource to have a partly independent renewal loss dynamics in the sink area, the variety of possible outcomes along a gradient of mixing rate is further increased. These outcomes are often strongly sensitive to the parameters of resource dynamics and interspecific interference competition. The implications of these results for biological conservation can be profound; detailed knowledge of interspecific interactions appears to be necessary to determine the effect of any land management that alters dispersal opportunities.
Rapid Diversity Loss of Competing Animal Species in Well-Connected Landscapes
PLOS ONE, 2015
Population viability of a single species, when evaluated with metapopulation based landscape evaluation tools, always increases when the connectivity of the landscape increases. However, when interactions between species are taken into account, results can differ. We explore this issue using a stochastic spatially explicit meta-community model with 21 competing species in five different competitive settings: (1) weak, coexisting competition, (2) neutral competition, (3) strong, excluding competition, (4) hierarchical competition and (5) random species competition. The species compete in randomly generated landscapes with various fragmentation levels. With this model we study species loss over time. Simulation results show that overall diversity, the species richness in the entire landscape, decreases slowly in fragmented landscapes whereas in well-connected landscapes rapid species losses occur. These results are robust with respect to changing competitive settings, species parameters and spatial configurations. They indicate that optimal landscape configuration for species conservation differs between metapopulation approaches, modelling species separately and meta-community approaches allowing species interactions. The mechanism behind this is that species in well-connected landscapes rapidly outcompete each other. Species that become abundant, by chance or by their completive strength, send out large amounts of dispersers that colonize and take over other patches that are occupied by species that are less abundant. This mechanism causes rapid species loss. In fragmented landscapes the colonization rate is lower, and it is difficult for a new species to establish in an already occupied patch. So, here dominant species cannot easily take over patches occupied by other species and higher diversity is maintained for a longer time. These results suggest that fragmented landscapes have benefits for species conservation previously unrecognized by the landscape ecology and policy community. When species interactions are important, landscapes with a low fragmentation level can be better for species conservation than well-connected landscapes. Moreover, our results indicate that metapopulation based landscape evaluation tools may overestimate the value of connectivity and should be replaced by more realistic meta-community based tools.
Theoretical Population Biology, 1997
Levins's unstructured metapopulation model predicts that the equilibrium fraction of empty habitat patches is a constant function of the fraction h of suitable patches in the landscape and that this constant equals the threshold value for metapopulation persistence. Levins's model thus suggests that the minimum amount of suitable habitat necessary for metapopulation persistence can be estimated from the fraction of empty patches at steady state. In this paper we construct several more realistic structured metapopulation models that include variation in patch quality and the rescue effect. These models predict both positive and negative correlations between the fractions of suitable patches and empty patches. The type of correlation depends in an intricate manner on the strength of the rescue effect and on the quality distribution of the patches to be destroyed. Empty patches can be considered as the resource limiting metapopulation growth. Our results demonstrate that the correlation between the fractions of suitable patches and empty patches is positive if and only if the average value of the resource decreases as the number of patches increases.
Conservation Biology, 2008
Abstract: Populations in agricultural landscapes often occur in source-sink situations: small patches of marginal habitat (sinks) are supported by an immigration flux from larger patches of high-quality habitat (sources). We sought to demonstrate that this situation occurs for Reed Warblers (Acrocephalus scirpaceus) in a riverine, mainly agricultural landscape in the Netherlands. We collected data on occurrence and habitat features in a large number of mostly small marshlands. We used a stochastic model to simulate the population dynamics in a metapopulation with sinks and sources. A statistical analysis of the field data, using regression techniques with occupation probability and abundance index as dependent variables, showed that habitat quality was less favourable in small habitat patches (e.g., ditches with reeds) than in larger patches ( large, heterogeneous marshlands). The spatial cohesion of the landscape also played an important role: abundance of breeding Reed Warblers in regions with low spatial cohesion was low. Local extinctions and recolonizations occurred, and their rates depended on the spatial parameters of the patch. This supports the hypothesis that metapopulation theory is applicable here. The results of the modeling study demonstrated that, besides the trivial dependence of sinks on sources, a larger amount of sink area and increased exchange of individuals increased the stability of source patches. This was shown not only by the larger size of the source population but also by increased resilience after a catastrophe. The area of the sink seemed less important than its distance to the source. The simulation indicated an optimal area of a few hectares (compared to a 10-ha area of the source) and a maximum distance of 2–5 km from the source. In creating sustainable landscapes, for example, by setting up an ecological network consisting of a limited number of high-quality patches, these small and seemingly insignificant habitat patches could play an important role and should be taken into consideration.Resumen: Las poblaciones en paisajes agrícolas ocurren frecuentemente en situaciones de fuente-sumidero: pequeños parches de hábitat marginal (sumideros) soportadas por un flujo de inmigración de parches más grandes de hábitat de alta calidad ( fuentes). Pretendemos demostrar que esta situación ocurre para el carricero común (Acrocephalus scirpaceus) en un paisaje ribereño, mayormente agrícola de los Países Bajos. Colectamos datos de presencia y características del hábitat en un número grande de pantanos, en su mayoría pequeños. Usamos un modelo estocástico para simular las dinámicas poblacionales en una metapoblación con sumideros y fuentes. Un análisis estadístico de los datos de campo, usando técnicas de regresión (con la probabilidad de ocupación y el índice de abundancia como variables dependientes), mostró que la calidad del hábitat fue menos favorable en los parches de hábitat pequeños (diques con carrizos) que en los parches grandes (pantanos heterogéneos grandes). La cohesión espacial del paisaje también jugó un papel importante: la abundancia de carriceros reproductores en regiones con poca cohesión espacial fue baja. Han ocurrido extinciones locales y recolonizaciones y sus tasas dependen de los parámetros espaciales del parche. Esto apoya la hipótesis de que la teoría de la metapoblación es aplicable aquí. Los resultados del estudio de modelado demostraron que, a pesar de la dependencia trivial de los sumideros con las fuentes, una cantidad mayor del área del sumidero y el aumento en el intercambio de individuos incrementó la estabilidad de los parches fuente. Esto no solo fue demostrado por el tamaño mayor de la población fuente, sino también por una mayor resiliencia posterior a una catástrofe. El área del sumidero parece ser menos importante que la distancia a la fuente. La simulación indica que unárea óptima de unas pocas hectáreas (comparada con las 10 ha de la fuente) y una distancia máxima de 2-5 km de ésta última. En la creación de paisajes sustentables ( por ejemplo al establecer una red ecológica consistente en un número limitado de parches de alta calidad), estos parches pequeños y aparentemente insignificantes pueden jugar un papel importante y deberían ser tomados en consideración.Resumen: Las poblaciones en paisajes agrícolas ocurren frecuentemente en situaciones de fuente-sumidero: pequeños parches de hábitat marginal (sumideros) soportadas por un flujo de inmigración de parches más grandes de hábitat de alta calidad ( fuentes). Pretendemos demostrar que esta situación ocurre para el carricero común (Acrocephalus scirpaceus) en un paisaje ribereño, mayormente agrícola de los Países Bajos. Colectamos datos de presencia y características del hábitat en un número grande de pantanos, en su mayoría pequeños. Usamos un modelo estocástico para simular las dinámicas poblacionales en una metapoblación con sumideros y fuentes. Un análisis estadístico de los datos de campo, usando técnicas de regresión (con la probabilidad de ocupación y el índice de abundancia como variables dependientes), mostró que la calidad del hábitat fue menos favorable en los parches de hábitat pequeños (diques con carrizos) que en los parches grandes (pantanos heterogéneos grandes). La cohesión espacial del paisaje también jugó un papel importante: la abundancia de carriceros reproductores en regiones con poca cohesión espacial fue baja. Han ocurrido extinciones locales y recolonizaciones y sus tasas dependen de los parámetros espaciales del parche. Esto apoya la hipótesis de que la teoría de la metapoblación es aplicable aquí. Los resultados del estudio de modelado demostraron que, a pesar de la dependencia trivial de los sumideros con las fuentes, una cantidad mayor del área del sumidero y el aumento en el intercambio de individuos incrementó la estabilidad de los parches fuente. Esto no solo fue demostrado por el tamaño mayor de la población fuente, sino también por una mayor resiliencia posterior a una catástrofe. El área del sumidero parece ser menos importante que la distancia a la fuente. La simulación indica que unárea óptima de unas pocas hectáreas (comparada con las 10 ha de la fuente) y una distancia máxima de 2-5 km de ésta última. En la creación de paisajes sustentables ( por ejemplo al establecer una red ecológica consistente en un número limitado de parches de alta calidad), estos parches pequeños y aparentemente insignificantes pueden jugar un papel importante y deberían ser tomados en consideración.
Hydrobiologia, 2012
Species are continuously lost and added to a local community. Dynamics of this process in a complex habitat mosaic (multiple habitats in a landscape), particularly of its rates (species turnover) are of primary concern for biodiversity conservation. Various studies suggest that species traits such as habitat specialization should affect species turnover. In communities where habitat specialization is a function of abiotic constraints, habitat specialists should respond faster to changing environment than generalists. We thus predicted a higher temporal turnover for specialists than for generalists in the presence of environmental variability (EV). In addition, we predicted that temporal turnover should decrease with increasing species richness of the communities they live in. We tested these predictions in a model system of 49 natural rock pools inhabited by 70 invertebrate species for which long-term (9 years) environmental and population dynamics data are available. We computed standard deviation of salinity measurements to represent EV for each pool. We further obtained the number of combined colonization and extinction events weighted by the number of years a species was recorded as a temporal turnover for each species in individual pools. We found that EV induced greater temporal turnover, however, the turnover depended on the species habitat traits (habitat specialization)-it has been higher in specialists but that relationship between EV and temporal turnover dissolved with increasing niche breadth (generalists). We further found that for some species, temporal turnover decreased with higher species richness and for other species, temporal turnover increased with higher species richness. The effect of species richness on temporal turnover was unrelated to species traits. This study suggests that whenever habitat is complex and heterogeneous and species pool diversified, local community dynamics becomes a composite of differential responses.
Ecological Applications, 2005
Forest fragmentation may cause increased brood parasitism and nest predation of breeding birds. In North America, nest parasitism and predation are expected to increase closer to forest edges because the brood-parasitic Brown-headed Cowbird (Molothrus ater) and generalist nest predators often enter the forest from adjoining developed (largely agricultural) habitats. Yet the abundance of brood parasites and nest predators at the patch scale may be strongly constrained by the total area of developed habitat at landscape scales. The scale and extent of landscape effects are unclear, however, because past studies were mostly conducted within local landscapes rather than across independent landscapes. We report replicated studies from 30 independent landscapes across 17 states of the United States that show that nest parasitism is strongly affected by fragmentation at a 20 km radius scale, equivalent to the maximum foraging range of cowbirds. Nest predation is influenced by both edge and landscape effects, and increases with fragmentation at a 10 km radius scale. Predation is additive to parasitism mortality, and the two together yield decreased population growth potential with increasing forest fragmentation at a 10 km radius scale for 20 of 22 bird species. Mapping of population growth potential across continental landscapes displays broad impacts of fragmentation on population viability and allows geographic prioritization for conservation.
Habitat fragmentation and biodiversity collapse in neutral communities
Ecological Complexity, 2004
Models of habitat fragmentation have mainly explored the effects on a few-species ecologies or on a hierarchical community of competitors. These models reveal that, under different conditions, ecosystem response can involve sharp changes when some given thresholds are reached. However, perturbations, recruitment limitation and other causes may prevent competitive hierarchies from actually operating in natural conditions: the process of competitive exclusion underlying hierarchies could not be a determinant factor structuring communities. Here we explore both spatially-implicit and spatially-explicit metapopulation models for a competitive community, where the colonization-extinction dynamics takes place through neutral interactions. Here species interactions are not hierarchical at all but are somehow ecologically equivalent and just compete for space and resources through recruitment limitation. Our analysis shows the existence of a common destruction threshold for all species: whenever habitat loss reaches certain value a sudden biodiversity collapse takes place. Furthermore, the model is able to reproduce species-rank distributions and its spatially explicit counterpart predicts also species-area laws obtained from recent studies on rainforest plots. It is also discussed the relevance of percolation thresholds in limiting diversity once the landscape is broken into many patches.
Effects of habitat destruction and resource supplementation in a predator-prey metapopulation model
We developed a mean "eld, metapopulation model to study the consequences of habitat destruction on a predator}prey interaction. The model complements and extends earlier work published by Bascompte and SoleH (1998, J. theor. Biol. 195, 383}393) in that it also permits use of alternative prey (i.e., resource supplementation) by predators. The current model is stable whenever coexistence occurs, whereas the earlier model is not stable over the entire domain of coexistence. More importantly, the current model permits an assessment of the e!ect of a generalist predator on the trophic interaction. Habitat destruction negatively a!ects the equilibrium fraction of patches occupied by predators, but the e!ect is most pronounced for specialists. The e!ect of habitat destruction on prey coexisting with predators is dependent on the ratio of extinction risk due to predation and prey colonization rate. When this ratio is less than unity, equilibrial prey occupancy of patches declines as habitat destruction increases. When the ratio exceeds one, equilibrial prey occupancy increases even as habitat destruction increases; i.e., prey &&escape'' from predation is facilitated by habitat loss. Resource supplementation reduces the threshold colonization rate of predators necessary for their regional persistence, and the bene"t derived from resource supplementation increases in a nonlinear fashion as habitat destruction increases. We also compared the analytical results to those from a stochastic, spatially explicit simulation model. The simulation model was a discrete time analog of our analytical model, with one exception. Colonization was restricted locally in the simulation, whereas colonization was a global process in the analytical model. After correcting for di!erences between nominal and e!ective colonization rates, most of the main conclusions of the two types of models were similar. Some important di!erences did emerge, however, and we discuss these in relation to the need to develop fully spatially explicit analytical models. Finally, we comment on the implications of our results for community structure and for the conservation of prey species interacting with generalist predators.
Ecological Modelling, 2002
An individual-based, spatially explicit stochastic lattice model, CAPS, was designed to examine multiple processes responsible for spatial patterns of abundance and diversity of sessile species in heterogeneous landscapes. Species simulated by CAPS differ in habitat preferences (niche width), dispersal of propagules, and relative fecundity. The spatial distribution of habitat types are represented as heterogeneous gridded landscapes. The outcome of competition and establishment processes in successive generations is determined locally via a seed lottery. A series of 200 year-long simulations was performed to investigate the effects of variation in species characteristics and competition, landscape heterogeneity, and disturbance on patterns of species abundances. The outcome of competition was most sensitive to differences in fecundity between species, the spatial distribution of suitable habitat and the initial distribution of species. Species with a narrow niche were confined to a single habitat type and remained at or near their initialization sites. Broader niches resulted in increasing niche overlap and competition but enhanced species mobility, allowing abundance levels to approach expected values determined by map resources. Even so, initial distributions still affected the spatial patterns of species distributions at year 200. Disturbance regimes were simulated by varying the frequency, extent and spatial pattern of disturbances. Disturbance events removed species from affected sites but did not otherwise alter habitat characteristics. Results showed that disturbances may lead to a reversal in competition and establishment, dependent on species-specific differences in fecundity and dispersal. Although intermediate levels of disturbance frequency and extent increased the probability of species coexistence, the spatial pattern of disturbance played an unexpectedly important role in the tradeoff between dispersal and fecundity. The ability to simulate multiple factors affecting patterns of persistence, abundance and spatial distribution of species provided by CAPS allows new insight into the temporal and spatial patterns of community development.