Habitat selection, including oviposition site choice, is an important driver of community assembly in freshwater systems. Factors determining patch quality are assessed by many colonising organisms ...and affect colonisation rates, spatial distribution and community structure. For many species, the presence/absence of predators is the most important factor affecting female oviposition decisions. However, individual habitat patches exist in complex landscapes linked by processes of dispersal and colonisation, and spatial distribution of factors such as predators has potential effects beyond individual patches. Perceived patch quality and resulting colonisation rates depend both on risk conditions within a given patch and on spatial context. Here we experimentally confirm the role of one context‐dependent processes, spatial contagion, functioning at the local scale, and provide the first example of another context‐dependent process, habitat compression, functioning at the regional scale. Both processes affect colonisation rates and patterns of spatial distribution in naturally colonised experimental metacommunities.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Since its inception, attempts have been made to improve ideal free distribution (IFD) theory to make it better fit real-world data. Spatial contagion is a newer ecological concept that suggests that ...the perceived quality of a patch can be affected by the quality of its neighbor patches. Here, we present a series of experiments testing for potential contagion effects, examining how contagion can interact with the IFD and determining whether spatial context affects assessment of habitat quality. First, we tested whether the presence of conspecific competitors negatively impacts oviposition habitat selection by female mosquitoes (Culex restuans). We then used a more complex spatial landscape to determine whether competition can create a spatial contagion effect. Finally, we examined whether the density of conspecifics can adjust the contagion effect of nutrient availability. While females avoided patches containing conspecifics, there was no effect of competition/density on neighboring patches. Additionally, we found that resource availability was a significant predictor of where egg rafts were laid, but resource availability did not have a contagion effect. These results provide further support for the utility of the IFD, as individuals were able to accurately assess patch-level habitat quality.
Abiotic conditions are important considerations in the species sorting process, which ultimately determines the distribution and abundance of species. Freshwater ecosystems will be impacted by ...ongoing temperature rise and other anthropogenically induced changes, such as nutrient enrichment and eutrophication. Changing characteristics of freshwater habitats will likely impact organisms in numerous ways, including through effects on colonization dynamics. Species are expected to colonize habitat patches where fitness will be the highest for themselves and their offspring, and how habitat selection interacts with changing environments remains an important question. We conducted a warming experiment to test the habitat selection preferences of aquatic beetles and hemipterans between habitat patches (mesocosms) of varying temperatures (via heaters), nutrient addition, and their interaction. Overall, insect abundance and richness were higher in unheated patches, with taxon-specific variation in response to heating. Although nutrients had limited effects on environmental conditions in mesocosms, their addition had no significant effects on insects. Insect assemblages had unique structures across heating treatments, with lower beta diversity and higher effective numbers of species in the warmest mesocosms. Our data support the importance of spatial variation in abiotic factors during the habitat selection process, and in determining species distributions and abundances as shallow lentic ecosystems are impacted by rising global temperatures.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The perceived quality of habitat patches in complex landscapes is highly context dependent. Characteristics of neighboring patches in such complex landscapes can influence perceived habitat quality, ...altering colonization dynamics and community structure. Spatial contagion of predation risk across patches has been observed over smaller spatial scales in aquatic systems. Naturally colonizing aquatic beetles were used to examine the spatial dynamics of risk contagion by quantifying the size of predator shadows around fish patches across spatial scales potentially involving numerous patches in natural landscapes. These consisted of fish free, replicate experimental mesocosm arrays radiating from larger central mesocosms containing fish, and allowed examination of the effect of distance to fish on beetle abundance, rarified species richness, and variation in species responses. Overall, beetles avoided pools closer to fish, but species varied in colonization pattern, resulting in species-specific predator shadows and potential behavioral species sorting. The spatial and phylogenetic extent of contagion and other context-dependent effects has implications for the role of complex behavior in the dynamics of communities and metacommunities.
Trophic interactions are critical determinants of community structure and ecosystem function. In freshwater habitats, top predators are traditionally viewed as drivers of ecosystem structure, shaping ...populations of consumers and primary producers. The temporary nature of small water bodies makes them dependent on colonization by many organisms, particularly insects that form highly diverse predator assemblages. We conducted mesocosm experiments with naturally colonizing populations of aquatic beetles to assess how prey (zooplankton) abundances influenced colonization and assemblages of natural populations of aquatic beetles. We experimentally demonstrate that zooplankton populations can be proximate regulators of predator populations and assemblages via prey-density-dependent predator recruitment. Our results provide support for the importance of prey populations in structuring predator populations and the role of habitat selection in structuring communities. We indicate that traditional views of predators as drivers of ecosystem structure in many systems may not provide a comprehensive picture, particularly in the context of highly disturbed or ephemeral habitats.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The role of habitat selection behaviour in the assembly of natural communities is an increasingly important theme in ecology. At the same time, ecologists and conservation biologists are keenly ...interested in scale and how processes at scales from local to regional interact to determine species distributions and patterns of biodiversity. How important is habitat selection in generating observed patterns of distribution and diversity at multiple spatial scales? In theory, habitat selection in response to interacting species can generate both positive and negative covariances among species distributions and create the potential to link processes of community assembly across multiple scales. Here I demonstrate that habitat selection by treefrogs in response to the distribution of fish predators functions at both the regional scale among localities and the local scale among patches within localities, implicating habitat selection as a critical link between local communities and the regional dynamics of metacommunities in complex landscapes.
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Predators play an extremely important role in natural communities. In freshwater systems, fish can dominate sorting both at the colonization and post-colonization stage. Specifically, for many ...colonizing species, fish can have non-lethal, direct effects that exceed the lethal direct effects of predation. Functionally diverse fish species with a range of predatory capabilities have previously been observed to elicit functionally equivalent responses on oviposition in tree frogs. We tested this hypothesis of functional equivalence of non-lethal effects for four predatory fish species, using naturally colonizing populations of aquatic beetles. Among taxa other than mosquitoes, and with the exception of the chemically camouflaged pirate perch, Aphredoderus sayanus, we provide the first evidence of variation in colonization or oviposition responses to different fish species. Focusing on total abundance, Fundulus chrysotus, a gape-limited, surface-feeding fish, elicited unique responses among colonizing Hydrophilidae, with the exception of the smallest and most abundant taxa, Paracymus, while Dytiscidae responded similarly to all avoided fish. Neither family responded to A. sayanus.Analysis of species richness and multivariate characterization of the beetle assemblages for the four fish species and controls revealed additional variation among the three avoided species and confirmed that chemical camouflage in A. sayanus results in assemblages essentially identical to fishless controls. The origin of this variation in beetle responses to different fish is unknown, but may involve variation in cue sensitivity, different behavioral algorithms, or differential responses to species-specific fish cues. The identity of fish species occupying aquatic habitats is crucial to understanding community structure, as varying strengths of lethal and non-lethal effects, as well as their interaction, create complex landscapes of predator effects and challenge the notion of functional equivalence.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Positive correlation of species richness with area is ubiquitous in nature, but the processes driving that relationship, as well as those constraining typical patterns, remain elusive. Patch size ...variation is pervasive in natural systems, and it is thus critical to understand how variation in patch size, as well as its potential interaction with factors like predation and isolation, affects community assembly. We crossed patch quality (fish presence/absence) with patch size to the examine effects of quality, size, and their interaction on colonization by aquatic insects. Overall, beetles favored small, fishless patches, but individual species sorted across patch size while hemipterans aggregated into large, fishless patches, producing sorting between Coleoptera and Hemiptera. Both patch size and predation risk generated significant variation in community structure and diversity. Patch size preferences for the 14 most abundant species and preeminence of species turnover in patterns of β-diversity reinforce patch size as a driver of regional species sorting via habitat selection. Species sorting at the immigration stage plays a critical role in community assembly. Identifying patch size as a component of perceived quality establishes patch size as a critical niche dimension and alters our view of its role in assembly dynamics and the maintenance of local and regional diversity.
Diversity in habitat patches is partly driven by variation in patch size, which affects extinction, and isolation, which affects immigration. Patch size also affects immigration as a component of ...patch quality. In wetland ecosystems, where variation in patch size and interpatch distance is ubiquitous, relationships between size and isolation may involve trade‐offs. We assayed treefrog oviposition at three patch sizes in arrays of two types, one where size increased with distance from forest (dispersed) and one with all patches equidistant from forest (equidistant), testing directly for an interaction between patch size and distance, which was highly significant. Medium patches in dispersed arrays received more eggs than those in equidistant arrays as use of typically preferred larger patches was reduced in dispersed arrays. Our results demonstrated a habitat selection trade‐off between preferred large and less‐preferred medium patches across small‐scale variation in isolation. Such patch size/isolation relationships are critical to community assembly and to understanding how diversity is maintained within a metapopulation and metacommunity framework, especially as wetland habitat becomes increasingly rare and fragmented. These results bring lessons of island biogeography, writ large, to bear on questions at small scales where ecologists often work and where habitat restoration is most often focused.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Avoiding detection is perhaps the ultimate weapon for both predators and prey. Chemosensory detection of predators via waterborne or airborne cues (predator‐released kairomones) is a key prey ...adaptation in aquatic ecosystems. Pirate perch, Aphredoderus sayanus, a largely insectivorous mesopredatory fish, are considered to be chemically camouflaged because they are unavoided by all colonizing organisms tested, including treefrogs and aquatic insects, despite stronger predatory effects on target taxa than several avoided fish. To address the mechanism behind camouflage we used aquatic insect colonization as a bioassay to test (1) whether increasing pirate perch density/biomass leads to increased avoidance, and (2) whether pirate perch mask heterospecific fish kairomones. Insect abundances, species richness, and community structure showed no response to pirate perch density. Last, pirate perch did not mask the kairomones of heterospecific predatory fish. Results support the idea that fish kairomones are species‐specific, and chemical camouflage is driven by a unique chemical signature that is either undetectable or has no negative associations for colonists.
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