Habitat preferences depend on substrate quality in a cooperative breeder

Coral reefs are complex three-dimensional habitats where the sizes, shapes, diversity and composition of hard corals influence the overall reef structure, and thus the provision of shelter for reef-associated species such as fish. Various metrics have been used to quantify ‘habitat complexity’ on coral reefs, yet debate persists regarding the most informative metric and how effectively the available metrics capture ecologically meaningful functions such as shelter provision. We used Coralcraft, a three-dimensional mechanistic model, to investigate how the morphological diversity and composition of coral communities influences habitat complexity at local (metres) scales. We developed new metrics of shelter to capture the mechanisms by which structure is likely important to reef species, accounting for factors such as the size of predator and prey and different hunting strategies. We simulated the growth of 13 coral community types with varying compositions of 10 common coral morphologies, calculating coral cover and 10 habitat complexity metrics (six novel and four well-established) over a five-year period. We found that more diverse coral communities did not always have the greatest structural complexity and shelter, in part due to certain morphologies having disproportionate influence on the resulting habitat complexity. Communities with lower structural complexity did not necessarily provide less shelter. The relationship between coral cover and habitat complexity metrics varied widely between different communities and was often nonlinear. We conclude that accounting for the morphological composition of coral communities can vastly improve the ability to predict or infer habitat complexity—both structural complexity and shelter provision—from measures of coral cover.

The Evolution of Social Behaviour

Do predation risk and food availability modify prey and mesopredator microhabitat selection in eelgrass (Zostera marina) habitat?

Forest structure is of functional importance for ecosystem stability and resilience, as well as for numerous other ecosystem functions and services. In this context, a high structural complexity can have a positive effect on diverse functions and services. Silvicultural management has the potential to negatively or positively affect forest structure and its complexity. In order to investigate the relationship between silvicultural management and forest structure, one first has to quantify forest structure and its complexity. To do so, various 3D measures based on terrestrial laser scanning data were used to quantify forest structure and structural complexity along a management gradient. The main objective of the thesis was to investigate the impact of different management systems on the structure of European forests and to compare them with formerly managed and primary forests. As beech (Fagus sylvatica L.) is the natural dominating tree species in Europe, beech-dominated forests were selected for this study. First, the understory complexity index (UCI) was introduced as a measure to describe the structural complexity of the forest understory (chapter 2). The UCI is based on the fractal dimension of a cross-sectional horizontal polygon, which represents the forest understory between 0.8 and 1.5 m. It is a density-dependent measure. Forest stands with advanced tree regeneration, as e.g. thickets, showed high UCI values compared to forest stands with a lower regeneration density. Comparing different management systems and forest types, the results revealed that the understory complexity was either large during the early phases of stand development or when the senescence of trees has largely proceeded, as found in beech primary forests. The second research aim of the study was to investigate, how structural complexity express itself in terms of the spatial distribution and density of plant material and how forest management influences these structural attributes (chapter 3). For that purpose, the structural complexity, as well as the density and spatial distribution of plant material within different forest strata of differently managed and unmanaged beech forests were quantified. The results showed that forest strata with a rather high structural complexity were characterized by a rather high density and a random to regular distribution of plant material. This could be observed for the primary beech forests and uneven-aged beech stands. Forest strata with a low structural complexity, as found in formerly managed forests, showed in contrast a rather low density and a clustered distribution of plant material. It can be assumed that structural complexity increases with increasing density and increasing homogeneity of the spatial distribution of plant material within a forest stand. Finally, the focus was on analyzing the influence of the understory complexity and vertical heterogeneity on the overall stand structural complexity of beech-dominated forests. The sub-study (chapter 4) on short-term dynamics of structural complexity revealed for uneven-aged stands that an increase of the understory complexity lead to an increase in the overall stand structural complexity. In this context, the initial canopy openness positively influenced the development of a complex understory and thus the overall structural complexity. Whereas in the younger, even-aged beech stands, an increase of vertical stratification positively influenced the stand structural complexity. In summary, short-term dynamics of stand structural complexity strongly depend on the developmental stage or canopy openness of the forest. This thesis not only contributes to the understanding of structural complexity and its relationship with other structural attributes, but also provides information on structural characteristics of different forest types. Managed and primary beech forests can be quite similar in terms of structural complexity. Especially, single-tree selection cutting seems to be a useful management approach for creating a complex stand structure. Furthermore, the thesis particularly highlighted the structural importance of the forest understory for the development of a complex stand structure. Therefore, management interventions could especially focus on the creation of complex understory structures, especially in early developmental stages, if an enhancement of structural complexity is desired. Lastly, the study demonstrated the wide range of potential applications of terrestrial laser scanning data for forest structure analysis.

Effects of sentence-structure complexity on speech initiation time and disfluency

The structural complexity of vegetation can have profound effects on the hunting efficiency of predators, thereby affecting their intake rate of prey. While studies have shown that vegetation complexity can play an important role in managing unwanted impacts of predators, it is less clear how structural complexity of invasive vegetation affects the vulnerability of terrestrial prey. Short nonnative pasture species bred for agricultural production, for example, are highly invasive and pervade grassland ecosystems worldwide. They generally have low structural complexity compared with taller native vegetation they often displace. We conducted controlled experiments to test whether nonnative pastures expose fauna to greater predation risk. Survival of invertebrates (tethered locusts) subject to predation by invasive mammalian insectivores (European hedgehogs) in nonnative pasture (0.10 per 24h; 95% CI, 0.08-0.13) was less than one-half that in structurally complex native perennial tussock (bunch) grass (0.24; 95% binomial CI, 0.18-0.31). A significant positive relationship was apparent between structural complexity (grass dry stem density) surrounding each locust and their survival. In a second experiment, survival of locusts placed solely in tussock increased with decreasing locust density in tussock, presumably reflecting fewer resource-rich patches on which predators could focus. These results demonstrate that invasion by structurally simple nonnative vegetation exposes prey to greater risk of predation. This is concerning from a global nature conservation perspective given that conversion of nearly one-half of the world's temperate grasslands to agriculture includes a range of invasive, structurally simple, nonnative, plant species. Minimizing invasion and maintaining and restoring complex habitat structure may be a useful conservation option for reducing unwanted predation.

Several studies have shown that habitat complexity is an important factor for the dynamic and stability of interacting species. However, it is not known how the habitat complexity may affect the tolerance of wasp-flower interactions to local extinction. Based on this perspective, in this study, we aimed to compare the tolerance of wasp flower visiting guild to local extinction in two different types of vegetation (Riparian Forest and Rocky Grassland). Through observations made during one year, we verified that the structure of the plant-wasp interaction network differed between the two areas, as well as that the robustness to cumulative extinctions had different patterns. The simulations of cumulative removal of species showed that the network in the Riparian Forest is more robust against the removal of both plants and wasps than that network in Rocky Grassland, since their extinction curves declined more slowly. Therefore, in our study area, we demonstrate that social wasp-plant interactions in areas with lower structural complexity are less tolerant to extinction (i.e. more fragile). We therefore suggest that studies that aim at biodiversity conservation should focus not only in areas where diversity is high, but also in area with lower species richness for the conservation of ecological roles within communities.

Preference for habitats with low structural complexity in the praying mantid Ciulfina sp. (Mantidae)

In shallow reservoirs, seasonal water drawdowns expose littoral areas and over time produce barren mudflats. When flooded, mudflats provide homogeneous substrates, turbid water, and eroding shorelines of limited ecological value. We hypothesized that in mudflats structurally complex habitats are occupied by more fish, smaller fish of a larger range in sizes, more species, and fish assemblages that are different from those in simpler habitats. We tested these hypotheses over two consecutive years with fish collections made in sites with varying structural complexity. Results indicated that structural complexity harbors more fish in transects and enclosures. Structural complexity did not influence median length, but length range increased with structural complexity. Average species richness increased with structural complexity. Fish assemblage composition changed as structural complexity increased. The ability of cover to provide survival, growth, and carrying capacity benefits is fundamental to programs aimed at increasing structural complexity. Results suggest observed effects on fish assemblages can lead to such benefits. Considering mudflats are a major component of reservoirs, expand as reservoirs age, and there is a potential to exert meaningful change on fish assemblages of impounded rivers by managing mudflats, we suggest additional attention is needed to develop practical habitat restoration options.

Across vertebrates, there is a broad correlation between neuroanatomy and the type of habitat preferred by a species. In general, species occupying habitats classified as more structurally complex have relatively larger brains and exaggerated structures related to navigating and exploiting those habitats. We empirically measured the structural habitat complexity of six species of Puerto Rican Anolis lizards, which have traditionally been classified as occupying three distinct habitat types. We also measured the volume of the whole brain as well as six structures putatively related to exploiting complex habitats in these species. We found a significant interspecific variation in structural habitat complexity, including a substantial variation between those belonging to the same ecomorph category. Despite this, we found no evidence to support the hypothesis that interspecific differences in habitat preferences, particularly differences in the relative structural complexity of those habitats, can favor a divergence in neuroanatomy. However, our findings indicate that, at a finer scale, species preferences for structural habitats vary greatly between Anolis species belonging to the same ecomorph category. This variation might contribute to the community structure of anoles by allowing multiple sympatric species of the same ecomorph category to occupy what, at a coarse scale, appears to be the same structural niche. We propose that, in the case of arboreal species, differences in the complexity of arboreal habitats alone may not be sufficient to favor divergent brain evolution.

The sea urchin Pseudechinus magellanicus is a dominant species in coastal habitats of southern Argentina and Chile. This study investigates its size distribution, abundance, and spatial arrangement in relation to coastal environmental gradients and habitat complexity along a depth gradient in central Patagonia (Argentina) during the austral spring. P. magellanicus exhibited a unimodal response to depth, with lower densities observed at intertidal levels and depths greater than 12 m. Size distribution showed depth-related patterns, with larger individuals prevalent at subtidal levels, intermediate sizes more common in intertidal and shallow depths, and recruits and juveniles most abundant at the infralittoral fringe and subtidal zones. A positive relationship between structural complexity and sea urchin densities was found, especially for smaller size classes. Conversely, larger individuals tended to inhabit areas with lower structural complexity and higher food availability. Sedimentation impacted the vertical distribution, particularly affecting recruits, juveniles, and young adults. Spatial arrangement analysis showed that aggregation is the predominant pattern along the coastal depth gradient. However, at depths of 3-5 m, where the kelp forest (Macrocystis pyrifera) dominates, recruits, juveniles, and intermediate-sized sea urchins displayed a less aggregated, more random distribution. These findings reveal the critical role of habitat complexity and depth in shaping the population dynamics of P. magellanicus and highlight the adaptability of this species to varying habitat conditions and its potential as an indicator of coastal ecosystem health.

As predation is a primary driver of mortality, the need to minimize predation risk can shape prey behavior, influencing habitat selection and investment in vigilance. As structurally complex habitats can reduce predation risk, prey within heterogeneous environments may have evolved sensory abilities to locate them. In temperate rocky intertidal systems, fucoid seaweeds are a main source of structural complexity and can provide shelter for small organisms. This study examined the effects of predation risk on habitat selection in a tide pool-dwelling shrimp, Palaemon affinis, specifically testing whether predation risk drives preferences for fucoid seaweeds and if shrimps use chemical cues to locate fucoid-rich habitats. While tide pools with and without fucoids were equally abundant, P. affinis densities were >3 times higher in pools containing fucoids. The relationship between P. affinis and fucoids appears to be related to predation risk with P. affinis exhibiting a preference for fucoid microhabitats when a potential predator was present. Shrimps could distinguish between olfactory signatures from tide pools with and without fucoids and the odor of fucoids from other marine algae, suggesting that chemical cues are used to identify these structurally complex habitats. In addition to reducing predation risk, fucoid-rich habitats may provide better access to essential resources and reduce exposure to other biotic and abiotic stressors. This study shows that prey organisms can rapidly modify habitat use based on ambient predation risk, with olfactory cues used to identify the shelter characteristics of different habitats. Predation is the major source of mortality for most animal species. For this reason, animals may have evolved ways to minimize predation risk by modifying their behavior. In this study, we show that small tide pool-dwelling shrimps modify their habitat use in response to predators, using chemical cues to locate and identify structurally complex habitats that could reduce predation risk when this risk is high.

Predator Avoidance and Diel Patterns of Microhabitat Use by Larval Tiger Salamanders

Mesopredator foraging success in eelgrass (Zostera marina L.): Relative effects of epiphytes, shoot density, and prey abundance

This paper presents strategies for spectral de- noising of hyperspectral images and 3-D data cube reconstruction from a limited number of tomographic measurements, arising in single snapshot imaging systems. For de-noising the main idea is to exploit the incoherency between the algebraic complexity measure, namely the low rank of the noise-free hyperspectral data cube, and the sparsity structure of the spectral noise. In particular, the non-noisy spectral data, when stacked across the spectral dimension, exhibits low-rank due to a small number of species. On the other hand, under the same representation, the spectral noise exhibits a banded structure. Motivated by this we show that the de-noised spectral data and the unknown spectral noise and the respective bands can be simultaneously estimated through the use of a low-rank and simultaneous sparse minimization operation without prior knowledge of the noisy bands. This result is novel for hyperspectral imaging applications and we compare our results with several existing methods for noisy band recovery. For recovery under limited tomographic projections we exploit both the low algebraic and structural complexity of the data cube via joint rank penalization plus Total Variation/wavelet domain sparsity, which is novel for single snapshot hyperspectral imaging systems. We combine these two approaches for simultaneous spectral de-noising and data cube recovery under limited measurements. We perform extensive simulations and our main result indicates that exploiting both low algebraic and structural complexity has a superior performance compared to exploiting only the structural complexity. To address the computational challenges associated with the resulting optimization problem we adapt several recent developments in the area of convex optimization, specifically employing splitting and proximal point based methods.