Three-dimensional interstitial space mediates predator foraging success in different spatial arrangements

Intertidal habitat complexity influences the density of the non-native crab Hemigrapsus sanguineus

Habitat structural complexity can provide protection from predators, potentially affecting population density of native and non-native prey. The invasive Asian shore crab, Hemigrapsus sanguineus, occurs in variable densities in the rocky intertidal zone of eastern North America and northern Europe, often in densities greater than in its native range. The present study examined the influence of habitat complexity on the density of H. sanguineus. Artificial shelters of concrete pavers with stones arranged in increasing complexity were deployed in the intertidal zone along a rocky shore in southeastern Massachusetts, USA, for 21 consecutive weekly intervals in 2020. Crabs consistently reached the highest densities in the most complex shelters despite their lower internal surface area. In addition, crabs exhibited shelter selectivity based on body size, with large crabs occupying artificial shelters in greater numbers than adjacent natural substrate. In a subsequent lab study, crab activity over 1 h was observed in the presence of the same artificial shelters, under simulated tidal conditions. Shelter complexity had little influence on the number of crabs under the pavers although crabs were more active when submerged in water than exposed to air. These results show that crab density increases as habitat complexity increases, and complexity may serve as a predictor of H. sanguineus density but not short-term behavior.

Vegetation and vantage point influence visibility across diverse ecosystems: Implications for animal ecology

Visual information can influence animal behavior and habitat use in diverse ways. Visibility is the property that relates 3D habitat structure to accessibility of visual information. Despite the importance of visibility in animal ecology, this property remains largely unstudied. Our objective was to assess how habitat structure from diverse environments and animal position within that structure can influence visibility. We gathered terrestrial lidar data (1 cm at 10 m) in four ecosystems (forest, shrub-steppe, prairie, and desert) to characterize viewsheds (i.e., estimates of visibility based on spatially explicit sightlines) from multiple vantage points. Both ecosystem-specific structure and animal position influenced potential viewsheds. Generally, as height of the vantage point above the ground increased, viewshed extent also increased, but the relationships were not linear. In low-structure ecosystems (prairie, shrub-steppe, and desert), variability in viewsheds decreased as vantage points increased to heights above the vegetation canopy. In the forest, however, variation in viewsheds was highest at intermediate heights, and markedly lower at the lowest and highest vantage points. These patterns are likely linked to the amount, heterogeneity, and distribution of vegetation structure occluding sightlines. Our work is the first to apply a new method that can be used to estimate viewshed properties relevant to animals (i.e., viewshed extent and variability). We demonstrate that these properties differ across terrestrial landscapes in complex ways that likely influence many facets of animal ecology and behavior.

3D printed objects do not impact the behavior of a coral-associated damselfish or survival of a settling stony coral

3D printing technology offers significant advantages in the development of objects and tools across an array of fields and has been implemented in an increasing number of ecological studies. As rates of degradation or chemical leaching of 3D printed models has not been well documented under environmental conditions, it is essential to examine if these objects will alter the behavior or impact the survivorship of the focal species prior to widespread implementation. Here, we explored the efficacy of using 3D printed models in coral reef behavioral research, an area of study where this form of additive manufacturing could offer significant advantages. Coral-associated blue-green chromis (Chromis viridis) individuals were exposed to natural and 3D printed coral habitats, and larval mustard hill coral (Porites astreoides) were offered 3D printed substrate as a settlement surface. Habitat association and behavioral analyses indicated that C. viridis did not discriminate or display modified behaviors between 3D printed and natural coral skeletons or between 3D printed materials. P. astreoides displayed significantly higher settlement when provided with 3D printed settlement surfaces than when provided with no settlement surface and settled at similar rates between 3D printed surfaces of differing materials. Additionally, growth and mortality of P. astreoides settled on different 3D printed surfaces did not significantly differ. Our results suggest that the 3D printed models used in this study are not inherently harmful to a coral reef fish or species of brooding coral, supporting further exploration of the benefits that these objects and others produced with additive manufacturing may offer as ecological research tools.

Habitat with small inter-structural spaces promotes mussel survival and reef generation

Spatially complex habitats provide refuge for prey and mediate many predator-prey interactions. Increasing anthropogenic pressures are eroding such habitats, reducing their complexity and potentially altering ecosystem stability on a global scale. Yet, we have only a rudimentary understanding of how structurally complex habitats create ecological refuges for most ecosystems. Better informed management decisions require an understanding of the mechanisms underpinning the provision of physical refuge and this may be linked to prey size, predator size and predator identity in priority habitats. We tested each of these factors empirically in a model biogenic reef system. Specifically, we tested whether mortality rates of blue mussels (Mytilus edulis) of different sizes differed among: (i) different forms of reef structural distribution (represented as 'clumped', 'patchy' and 'sparse'); (ii) predator species identity (shore crab, Carcinus maenas and starfish, Asterias rubens); and (iii) predator size. The survival rate of small mussels was greatest in the clumped experimental habitat and larger predators generally consumed more prey regardless of the structural organisation of treatment. Small mussels were protected from larger A. rubens but not from larger C. maenas in the clumped habitats. The distribution pattern of structural objects, therefore, may be considered a useful proxy for reef complexity when assessing predator-prey interactions, and optimal organisations should be considered based on both prey and predator sizes. These findings are essential to understand ecological processes underpinning predation rates in structurally complex habitats and to inform future restoration and ecological engineering practices.

Benefits and limitations of three-dimensional printing technology for ecological research

BACKGROUND

Ecological research often involves sampling and manipulating non-model organisms that reside in heterogeneous environments. As such, ecologists often adapt techniques and ideas from industry and other scientific fields to design and build equipment, tools, and experimental contraptions custom-made for the ecological systems under study. Three-dimensional (3D) printing provides a way to rapidly produce identical and novel objects that could be used in ecological studies, yet ecologists have been slow to adopt this new technology. Here, we provide ecologists with an introduction to 3D printing.

RESULTS

First, we give an overview of the ecological research areas in which 3D printing is predicted to be the most impactful and review current studies that have already used 3D printed objects. We then outline a methodological workflow for integrating 3D printing into an ecological research program and give a detailed example of a successful implementation of our 3D printing workflow for 3D printed models of the brown anole, Anolis sagrei, for a field predation study. After testing two print media in the field, we show that the models printed from the less expensive and more sustainable material (blend of 70% plastic and 30% recycled wood fiber) were just as durable and had equal predator attack rates as the more expensive material (100% virgin plastic).

CONCLUSIONS

Overall, 3D printing can provide time and cost savings to ecologists, and with recent advances in less toxic, biodegradable, and recyclable print materials, ecologists can choose to minimize social and environmental impacts associated with 3D printing. The main hurdles for implementing 3D printing-availability of resources like printers, scanners, and software, as well as reaching proficiency in using 3D image software-may be easier to overcome at institutions with digital imaging centers run by knowledgeable staff. As with any new technology, the benefits of 3D printing are specific to a particular project, and ecologists must consider the investments of developing usable 3D materials for research versus other methods of generating those materials.