Non-random seasonal variation in the structure of a Mediterranean snake community

Abstract. The community structure in relation to habitat type was studied in a Mediterranean community of snakes from Canale Monterano, central Italy. Habitat data for snakes were analysed both overall and divided by season, i.e. spring (April–June) and summer (July–September). Community analyses were performed using null models (RA2 and RA3 algorithms) and Monte Carlo simulations on habitat niche overlap estimates. Null models suggested that the community was assembled non-randomly (according to RA2 but not RA3), indicating that the generalist-specialist nature (the number of resource states, but not necessarily the types) used by each species in the assemblage reduced ecological similarity. Similar results were reached also performing the same null model procedures on the spring datasets, whereas no structure emerged during summer either by RA2 or RA3 algorithms. In general, this study suggests that the community structure of snakes during spring may be shaped by the different eco-physiological needs of the various species (probably, the differential tolerance to cold and the consequent needs of finding suitable hibernacula), whereas the lack of structure during summer may be caused by the between-species similar foraging needs.

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Null model analysis of lizard communities in five urban parks of Rome

Amphibia-Reptilia ◽

10.1163/156853807782152516 ◽

2007 ◽

Vol 28 (4) ◽

pp. 547-553 ◽

Cited By ~ 5

Author(s):

Luca Luiselli ◽

Lorenzo Rugiero

Keyword(s):

Community Structure ◽

Central Italy ◽

Habitat Type ◽

Null Model ◽

Urban Parks ◽

Habitat Types ◽

Podarcis Muralis ◽

Green Areas ◽

Assembly Structure ◽

Natural Communities

Abstract Null models are an essential tool for investigating structure in natural communities of animals, including reptiles. In this paper, we studied the assembly structure of a lizard community constituted by four species (Lacerta bilineata, Podarcis muralis, P. sicula, Chalcides chalcides) along 25 different transects, each 300 m long and representing a specific habitat type, in five independent urban green areas in Rome, central Italy. Lacerta bilineata was observed in 92% of the total transects (n = 25), P. muralis in 100%, P. sicula in 72%, and C. chalcides in 52%. Based on the number of lizards observed along the various transects, it seemed that each species was linked especially to particular habitat types within each study area, but that the habitat types frequented by each species were not necessarily exactly the same across the study areas. Null model analyses revealed that the lizard community was not randomly organized in four of five study areas by RA2 (thus denoting that the generalist-specialist nature of the species reduced ecological similarity) but not by RA3 algorithms (thus denoting that the types of resources used did not reduce ecological similarity). Thus, the community structure was due mainly to the different specialist-generalist nature of the various co-occurring species.

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Diet and niche breadth and overlap in fish communities within the area affected by an Amazonian reservoir (Amapá, Brazil)

Anais da Academia Brasileira de Ciências ◽

10.1590/0001-3765201420130053 ◽

2014 ◽

Vol 86 (1) ◽

pp. 383-406 ◽

Cited By ~ 18

Author(s):

JÚLIO C. SÁ-OLIVEIRA ◽

RONALDO ANGELINI ◽

VICTORIA J. ISAAC-NAHUM

Keyword(s):

Community Structure ◽

Seasonal Variation ◽

Fish Species ◽

Niche Breadth ◽

Null Model ◽

Stomach Contents ◽

Physical Conditions ◽

River Damming ◽

Standard Configuration ◽

Feeding Resources

We investigated the niche breadth and overlap of the fish species occurring in four environments affected by the Coaracy Nunes reservoir, in the Amapá Brazilian State. Seasonal samples of fishes were taken using a standard configuration of gillnets, as well as dragnets, lines, and castnets. Five hundred and forty stomach contents, representing 47 fish species were analyzed and quantified. Niche breadth and overlap were estimated using indexes of Levins and Pianka, respectively, while interspecific competition was evaluated using a null model (RA3). ANOVA and the KruskalWallis test were used, respectively, to evaluate differences in niche breadth and overlap between areas. The data indicate that the majority of the fish species belong to the piscivore, omnivore, and detritivore guilds. These species have likely colonized the environments due to the availability of suitable feeding resources, and the favorable physical conditions created by the river damming. Overall, few species have ample niches, but most of them are highly specialized. Resources seasonal variation had little effect on the feeding behavior of most species in the study areas. The null models indicated that competition was not a factor determining on community structure.

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Benthic macroinvertebrate communities in sites with native forest presence and absence in north Patagonia

Iheringia Série Zoologia ◽

10.1590/1678-4766e2020014 ◽

2020 ◽

Vol 110 ◽

Author(s):

Patricio De los Ríos-Escalante ◽

Carlos Esse ◽

Rodrigo Santander-Massa ◽

Pablo Saavedra ◽

Francisco Encina-Montoya

Keyword(s):

Species Composition ◽

Neutral Theory ◽

Null Model ◽

Niche Overlap ◽

Null Models ◽

Species Number ◽

Group Method ◽

Native Forest ◽

Macroinvertebrate Communities ◽

Nothofagus Forests

ABSTRACT The benthic fauna in northern Patagonian streams is characterized by presence of water quality indicator species. The aim of the present study was characterized the benthic communities in streams associated to sites with presence of Nothofagus forests and with human intervention without Nothofagus forests using null models in ecology, unified neutral theory of biodiversity (UNTB) and unweighted pair group method with arithmetic mean (UPGMA). The results of species co-occurrence null model revealed that species associations are random, whereas the results of niche overlap null models revealed the presence of niche overlap. The UNTB results revealed low species number. The results of UPGMA revealed that species composition is specific for each site existing marked differences. The exposed results agree with results observed for central and northern Patagonian Chilean rivers, where the species composition is variable in according to surrounding basin properties and seasonal conditions.

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Macro-habitat preferences by the African manatee and crocodiles – ecological and conservation implications

Web Ecology ◽

10.5194/we-12-39-2012 ◽

2012 ◽

Vol 12 (1) ◽

pp. 39-48 ◽

Cited By ~ 1

Author(s):

L. Luiselli ◽

G. C. Akani ◽

N. Ebere ◽

F. M. Angelici ◽

G. Amori ◽

...

Keyword(s):

Habitat Selection ◽

Coastal Lagoons ◽

Habitat Preferences ◽

Habitat Type ◽

Null Model ◽

Niche Overlap ◽

West African ◽

Conservation Implications ◽

Type Selection ◽

Selection Of

Abstract. African manatees (Trichechus senegalensis) and crocodiles are threatened species in parts of their range. In West Africa, crocodiles may constitute the main predators for manatees apart from humans. Here, we explore the macro-habitat selection of manatees and two species of crocodiles (West African crocodiles Crocodylus suchus and dwarf crocodile Osteolaemus tetraspis) in the Niger Delta (Nigeria), testing the hypotheses that (i) manatees may avoid crocodiles in order to minimize risks of predation, and (ii) the two crocodile species do compete. The study was carried out between 1994 and 2010 with a suite of different field techniques. We observed that the main macro-habitat types were freshwater rivers and coastal lagoons for manatees, mangroves for West African crocodiles, and rivers and creeks for dwarf crocodiles, with (i) the three species differing significantly in terms of their macro-habitat type selection, and (ii) significant seasonal influence on habitat selection of each species. Null models for niche overlap showed a significantly lower overlap in macro-habitat type use between manatee and crocodiles, whereas the two crocodiles were relatively similar. Null model analyses did not indicate any competitive interactions between crocodiles. On the other hand, manatees avoided macro-habitats where crocodiles, and especially West African crocodiles, are abundant.

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A new dispersal-informed null model for community ecology shows strong performance

10.1101/046524 ◽

2016 ◽

Author(s):

Eliot Miller

Keyword(s):

Community Structure ◽

Competitive Exclusion ◽

Null Model ◽

Error Rates ◽

Null Models ◽

Type I ◽

Habitat Filtering ◽

Exclusion Processes ◽

Phylogenetic Community Structure ◽

Structure Metrics

AbstractNull models in ecology have been developed that, by maintaining some aspects of observed communities and repeatedly randomizing others, allow researchers to test for the action of community assembly processes like habitat filtering and competitive exclusion. Such processes are often detected using phylogenetic community structure metrics. When biologically significant elements, such as the number of species per assemblage, break down during randomizations, it can lead to high error rates. Realistic dispersal probabilities are often neglected during randomization, and existing models make the oftentimes empirically unreasonable assumption that all species are equally probable of dispersing to a given site. When this assumption is unwarranted, null models need to incorporate dispersal probabilities. I do so here, and present a dispersal null model (DNM) that strictly maintains species richness, and approximately maintains species occurrence frequencies and total abundance. I tested its statistical performance when used with a wide breadth of phylogenetic community structure metrics across 3,000 simulated communities assembled according to neutral, habitat filtering, and competitive exclusion processes. The DNM performed well, exhibiting low error rates (both type I and II). I also implemented it in a re-analysis of a large empirical dataset, an abundance matrix of 696 sites and 75 species of Australian Meliphagidae. Although the overall signal from that study remained unchanged, it showed that statistically significant phylogenetic clustering could have been an artifact of dispersal limitations.

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Diet and habitat-niche relationships within an assemblage of large herbivores in a seasonal tropical forest

Journal of Tropical Ecology ◽

10.1017/s0266467412000302 ◽

2012 ◽

Vol 28 (4) ◽

pp. 385-394 ◽

Cited By ~ 20

Author(s):

Farshid S. Ahrestani ◽

Ignas M. A. Heitkönig ◽

Herbert H. T. Prins

Keyword(s):

Seasonal Variation ◽

Habitat Selection ◽

South India ◽

Niche Breadth ◽

Niche Overlap ◽

Dry Season ◽

Wet Season ◽

Large Herbivores ◽

Axis Axis ◽

Habitat Niche

Abstract:There is little understanding of how large mammalian herbivores in Asia partition habitat and forage resources, and vary their diet and habitat selection seasonally in order to coexist. We studied an assemblage of four large herbivores, chital (Axis axis), sambar (Cervus unicolor), gaur (Bos gaurus) and Asian elephant (Elephas maximus), in the seasonal tropical forests of Bandipur and Mudumalai, South India, and tested predictions regarding the species’ seasonal diet browse : graze ratios, habitat selection and habitat-niche preference and overlap. Field data collected for the study included the seasonal variation in grass quality, the seasonal variation in δ13C in the species’ faeces and the seasonal variation in the species’ habitat selection and overlap using a grid-based survey. Results of the δ13C analyses showed that the chital was more of a grazer in the wet season (−17.9‰ to −21.6‰), but that it increased the proportion of browse in its diet in the dry season (−25.6‰ to −27.7‰); the gaur was a grazer for most of the year (−15.3‰ to −18.6‰); the sambar preferred to browse throughout the year (−21.1‰ to −30.4‰); and that the elephant was a mixed feeder (−14.2‰ to −21.4‰). Elephant habitat-niche breadth was high (0.53 in wet and 0.54 in dry) and overlapped equally with that of the other species in both seasons (0.39–0.94). The gaur had the most restricted habitat-niche breadth in both seasons (0.25 in wet and 0.28 in dry), and it switched from the moist deciduous habitat in the dry season to the dry deciduous habitat in the wet season. These results offer the first insights into the seasonal variation in browse : graze diet ratios and the habitat-niche overlap amongst the common largest-bodied mammalian herbivore species found in South India.

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Community structure of invertebrate fauna in Central Chilean Rivers

Acta Limnologica Brasiliensia ◽

10.1590/s2179-975x3718 ◽

2019 ◽

Vol 31 ◽

Author(s):

Patricio De los Ríos ◽

Gustavo Díaz ◽

Jorge Gonzalez ◽

Konrad Górski ◽

Evelyn Habit

Keyword(s):

Community Structure ◽

Interspecific Competition ◽

Niche Overlap ◽

Null Models ◽

Ecological Studies ◽

Invertebrate Fauna ◽

River Systems ◽

Central Chile ◽

Invertebrate Communities ◽

Ecological Patterns

Abstract Aim River systems of Central Chile are short, steep and fast flowing. They are characterized by discharge regimes dominated by rainfall and snowmelt. Invertebrate fauna is highly endemic. This study aimed to describe the community structure of invertebrate in eight river systems in Central Chile (33-39°S) using species co-occurrence and niche sharing null models. Methods Invertebrate samples were collected from Central Chilean rivers (33-39°S), data were analyzed co-occurrence species and niche sharing null models for determine potential structuring patterns. Results The results revealed the presence of non-structured patterns in co-occurrence considering each site as well as all sites, that is most probably an effect of presence of many repeated species in the studied sites. Furthermore, we found the existence of niche overlap due to interspecific competition at each site and among all sites. The results obtained from these river systems corroborate observations from Chilean Patagonian Rivers. Conclusion This study contributes to understanding of biogeographical and ecological patterns of invertebrate communities in central Chilean Rivers and provide foundations for more complex ecological studies.

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Habitat niche community-level analysis of an amphibian assemblage at Lake Nabugabo, Uganda

Web Ecology ◽

10.5194/we-8-125-2008 ◽

2008 ◽

Vol 8 (1) ◽

pp. 125-134 ◽

Cited By ~ 6

Author(s):

M. Behangana ◽

L. Luiselli

Keyword(s):

Community Structure ◽

Relative Abundance ◽

Resource Partitioning ◽

Community Organization ◽

Habitat Type ◽

Niche Overlap ◽

Seasonal Effects ◽

Wet Season ◽

Swamp Forest ◽

Score Analysis

Abstract. Community structure was studied across six different habitat types in an amphibian assemblage constituted by 24 species belonging to five families, from Lake Nabugabo, Uganda. We employed a suite of different statistical methods, including univariate, multivariate, and Monte Carlo procedures to investigate the randomness/nonrandomness and the seasonal effects (wet versus dry season) of the community assembly. We calculated for each species in each habitat type an index of relative abundance by using a time constrained counting technique, with 48 1-h counts for each habitat type. Co-occurrence was analysed by C score with 30 000 simulations; resource partitioning patterns by RA2 and RA3 algorithms with 30 000 simulations; and apparent dissimilarity among species in terms of habitat use by UPGMA dendrograms. After pooling data from wet and dry seasons, it resulted that the amphibian community was non-randomly assembled according to C-score analyses, but both RA2 and RA3 were unable to uncover any competitive structure for the dataset. Seasonal effects were evident, and although C score analyses confirmed a nonrandom structure for the community under study (particularly in wet season), RA3 showed that species with high relative abundance tended to significantly concentrate in one habitat type (swamp forest) rather than to partition the habitat resource. UPGMA dendrograms grouped the species differently in dry versus wet seasons. Overall, the comparative evidence of 1) non-random community structure according to C-score analysis, and 2) absence of resource partitioning according to niche overlap null models analysis, suggests that community organization in Lake Nabugabo amphibians is generated by habitat affinities rather than by interspecific competition.

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Phylogenetic community structure metrics and null models: a review with new methods and software

10.1101/025726 ◽

2015 ◽

Cited By ~ 1

Author(s):

Eliot T Miller ◽

Damien R Farine ◽

Christopher H Trisos

Keyword(s):

Community Structure ◽

Community Assembly ◽

Competitive Exclusion ◽

Null Model ◽

Error Rates ◽

Null Models ◽

Type I ◽

Habitat Filtering ◽

Phylogenetic Community Structure ◽

Structure Metrics

Competitive exclusion and habitat filtering are believed to have an important influence on the assembly of ecological communities, but ecologists and evolutionary biologists have not reached a consensus on how to quantify patterns that would reveal the action of these processes. No fewer than 22 phylogenetic community structure metrics and nine null models can be combined, providing 198 approaches to test for such patterns. Choosing statistically appropriate approaches is currently a daunting task. First, given random community assembly, we assessed similarities among metrics and among null models in their behavior across communities varying in species richness. Second, we developed spatially explicit, individual-based simulations where communities were assembled either at random, by competitive exclusion or by habitat filtering. Third, we quantified the performance (type I and II error rates) of all 198 approaches against each of the three assembly processes. Many metrics and null models are functionally equivalent, more than halving the number of unique approaches. Moreover, an even smaller subset of metric and null model combinations is suitable for testing community assembly patterns. Metrics like mean pairwise phylogenetic distance and phylogenetic diversity were better able to detect simulated community assembly patterns than metrics like phylogenetic abundance evenness. A null model that simulates regional dispersal pressure on the community of interest outperformed all others. We introduce a flexible new R package, metricTester, to facilitate robust analyses of method performance. The package is programmed in parallel to readily accommodate integration of new row-wise matrix calculations (metrics) and matrix-wise randomizations (null models) to generate expectations and quantify error rates of proposed methods.

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