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 b-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.

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Two of the most important factors determining community structure and diversity within and among habitat patches are patch size and patch quality. Despite the importance of patch size in existing paradigms in island biogeography, metapopulation biology, landscape ecology, and metacommunity ecology, and growing conservation concerns with habitat fragmentation, there has been little investigation into how patch size interacts with patch quality. We crossed three levels of patch size (1.13 m , 2.54 m and 5.73 m ) with two levels of patch quality (fish presence/absence, green sunfish [Lepomis cyanellus] and golden shiners [Notemigonus crysoleucus]) in six replicate experimental landscapes (3 × 2 × 6 = 36 patches). Both fish predators have been previously shown to elicit avoidance in ovipositing treefrogs. We examined how patch size and patch quality, as well as the interaction between size and quality, affected female oviposition preference and male calling site choice in a natural population of treefrogs (Hyla chrysoscelis). Females almost exclusively oviposited in the largest fishless patches, indicating that females use both risk, in the form of fish predators, and size itself, as components of patch quality. Females routinely use much smaller natural and experimental patches, suggesting that the responses to patch size are highly context dependent. Responses to fish were unaffected by patch size. Male responses largely mimicked those of females, but did not drive female oviposition. We suggest that patch size itself functions as another aspect of patch quality for H. chrysoscelis, and serves as another niche dimension across which species may behaviorally sort in natural systems. Because of strong, shared avoidance of fish (as well as other predators), among many colonizing taxa, patch size may be a critical factor in species sorting and processes of community assembly in freshwater habitats, allowing species to behaviorally segregate along gradients of patch size in fishless ponds. Conversely, lack of variation in patch size may concentrate colonization activity, leading to intensification of species interactions and/or increased use of lesser quality patches.

Predation risk and resource abundance are two primary characteristics that determine species abundances and community composition. Colonizing organisms should attempt to minimize the risk of mortality and maximize growth through selection of patches with the highest expected fitness. However, maximizing fitness across multiple gradients of patch quality involves accurate cue assessment, integration and behavioural responses that consider multiple factors that affect fitness simultaneously. Our goal was to simultaneously and factorially assess the effects of predation risk and resource abundance among an assemblage of aquatic insects to determine the relative importance of each factor, and whether the two factors interact to affect colonization, oviposition and community assembly. We conducted a field mesocosm experiment in which we crossed predator density (0, 1, 2 fish, Fundulus chrysotus) with supplemental nutrient abundance (0, 4, 8 g rabbit chow) in a 3 × 3 factorial design. We then assayed colonization by natural populations of aquatic beetles and oviposition by natural populations of Culex mosquitoes. We observed species‐specific responses, with many species avoiding fish and some selecting habitats with more nutrients. Nutrients and predator presence only interactively affected oviposition by Culex mosquitoes, and the effect of fish presence exceeded that of nutrients in all but one analysis. Our results illustrate the primacy of predation risk in generating colonization patterns and structuring communities in aquatic habitats, but that colonization responses to variation in multiple components of patch quality are often species‐specific. Simultaneous assessments of multiple aspects of patch quality allow for the determination of potential interactions among cue sources and the relative importance of various patch characteristics to colonizers. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13086/suppinfo is available for this article.

Colonisation is a critical process driving the abundances and diversity of species in spatially discrete communities. Although patch size and patch quality are well known as determinants of post‐colonisation species richness and abundance, less is known about how patch size affects colonisation. Patch size and quality may not be independent, so assessment of potential interactions is necessary for understanding patterns of species abundance in natural systems. In freshwater systems, presence and identity of predators is a dominant determinant of patch quality, with larger habitat patches often supporting larger and more diverse predator assemblages. To examine potential interactions, we manipulated patch size and quality (fish presence/absence) using naturally colonised experimental landscapes and assayed oviposition by Culex mosquitoes. Culex restuans selected patches that were smaller, did not contain fish, and had higher temperatures. We demonstrate that patch size, along with patch quality, can generate patterns of abundance at the colonisation stage that are contradictory to traditional patch size‐based models of species distributions.

Running the gauntlet of predators consumes critical time and energy resources, as all species are vulnerable to one or, typically, more predators at some life stage. Prey employ a vast array of mechanisms to avoid predation, and predators, likewise, come in a bewildering variety. Thus, defensive adaptations are rarely one size fits all. Considerable work has addressed multi-predator consumptive effects, but we now know that non-consumptive effects of predators can dramatically impact individuals, (meta)populations, and (meta)communities. However, little is known regarding the community-wide dynamics of non-consumptive effects generated by multiple predators. Predator avoidance by choosing a patch that is free of a particular predator or predators can be the most effective strategy if conditions at colonization are a reliable predictor of absence, which is often true for fish in freshwater systems. We experimentally manipulated composition of the predator assemblage in aquatic mesocosms in a substitutive design, with zero, one, two, or three caged predatory fish species (one benthic, one pelagic, and one surface fish) at constant density and biomass, and assayed responses of naturally colonizing aquatic insects. We addressed three related questions; first, how do members of a diverse assemblage of colonizing aquatic insects respond to this variation in species and species combinations, second, do individual species (and higher taxa), respond differently to single vs. multiple predator species (species richness), and third how do any responses to fish species and species combinations, and effects on species richness, translate into community-wide changes in the composition of colonists. Prey had varied responses to specific predators or combinations of predators, resulting in distinct community composition across treatments and higher β-diversity with predators. Prey showed emergent multi-predator effects, where certain species only responded to predator species combinations, but not to any individual predator, and stronger effects of multiple predator vs. single-predator treatments, despite strong responses to individual predators in many taxa. Habitat selection effects can range from the individual to the metacommunity, and the dynamics of habitat selection in response to predators is a complex function of predator identity, density, richness, species composition, and patch spatial context.

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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.