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Aggressive interactions during feeding between native and invasive freshwater turtles
Abstract
The red-eared slider (Trachemys scripta elegans) is a worldwide highly invasive species, currently introduced in most freshwater habitats as a consequence of massive pet
trade. In the Iberian Peninsula, this species is competing with and displacing the endangered native Spanish terrapin (Mauremys leprosa). Sliders are considered environmentally-aggressive turtles, capable of threatening or biting other individuals during competitive
activities such as feeding. We hypothesized that agonistic behavior of introduced sliders against native terrapins might negatively
affect the feeding efficiency of M. leprosa. We compared food ingestion of turtles and aggressive interactions during feeding, under situations of conspecific and heterospecific
competition. The amount of food ingested by native and introduced turtles was similar under conspecific competition, but T. scripta ingested a greater percentage of food supplied under heterospecific competition. Also, introduced sliders initiated most
of the aggressions observed during feeding activity, and aggression was more frequently directed to heterospecifics. Our results
suggest a more aggressive and competitive behavior of introduced T. scripta in vying for food resources, which might contribute to explain the observed displacement of native populations of M. leprosa.
KeywordsAggressiveness–Feeding competition–Freshwater turtles–Invasive species–
Mauremys leprosa
–
Trachemys scripta
... For example, bolder and more explorative individuals tend to have a higher rate of success in invading a new habitat [8]. Meanwhile, research has revealed that native species also exhibit individual variations in behavior during biological invasions, which is also related to the various ecologically important phenotypic traits such as personality [10,11]. ...
... The T. scripta elegans is listed as one of the 100 worst invasive species in the world [33]. The introduction of T. scripta elegans would lead to them competing with native freshwater turtle species and lead to the extinction of these native turtles in their native habitats, including species of Mauremys [11,32,33]. The native habitat of T. scripta elegans is similar to the habitat occupied by the Chinese pond turtle (Mauremys reevesii) [34]. ...
... T. scripta elegans can outcompete native M. reevesii for swimming speed and an advantage in feeding kinematics, such as shorter gape cycle time and neck retraction time [39,40]. These advantages may give the T. scripta elegans a competitive edge for food resources, nesting sites, and basking sites [11,32,41]. However, the interaction effects of personality traits in foraging behavior and fitness consequences (e.g., growth) in invasive T. scripta elegans and native M. reevesii have not been fully studied. ...
Simple Summary
Animal personalities could affect the behavior and physiology of both native and invasive species during biological invasion. However, little is known about the personality interaction effects on foraging behavior and growth between native and invasive species. We used the red-eared slider turtle and Chinese pond turtle as models to investigate how personality interactions effect the foraging behavior and growth of both these turtle species. The results showed that the foraging behavior of M. reevesii was mainly affected by the personality of T. scripta elegans. However, the foraging behavior of T. scripta elegans was effected by both their own personality and the personalities of M. reevesii. Additionally, the growth of both M. reevesii and T. scripta elegans were not effected by the personality combinations. The results revealed the mechanisms of personality interaction effects on the foraging behavior and growth of both native and invasive species during biological invasion. This study provides empirical evidence to help understand the effects of personalities on invasion dynamics.
Abstract
Animal personalities play a crucial role in invasion dynamics. During the invasion process, the behavioral strategies of native species vary among personalities, just as the invasive species exhibit variations in behavior strategies across personalities. However, the impact of personality interactions between native species and invasive species on behavior and growth are rarely illustrated. The red-eared slider turtle (Trachemys scripta elegans) is one of the worst invasive species in the world, threatening the ecology and fitness of many freshwater turtles globally. The Chinese pond turtle (Mauremys reevesii) is one of the freshwater turtles most threatened by T. scripta elegans in China. In this study, we used T. scripta elegans and M. reevesii to investigate how the personality combinations of native and invasive turtles would impact the foraging strategy and growth of both species during the invasion process. We found that M. reevesii exhibited bolder and more exploratory personalities than T. scripta elegans. The foraging strategy of M. reevesii was mainly affected by the personality of T. scripta elegans, while the foraging strategy of T. scripta elegans was influenced by both their own personality and personalities of M. reevesii. Additionally, we did not find that the personality combination would affect the growth of either T. scripta elegans or M. reevesii. Differences in foraging strategy may be due to the dominance of invasive species and variations in the superficial exploration and thorough exploitation foraging strategies related to personalities. The lack of difference in growth may be due to the energy allocation trade-offs between personalities or be masked by the slow growth rate of turtles. Overall, our results reveal the mechanisms of personality interaction effects on the short-term foraging strategies of both native and invasive species during the invasion process. They provide empirical evidence to understand the effects of personality on invasion dynamics, which is beneficial for enhancing comprehension understanding of the personality effects on ecological interactions and invasion biology.
... Multiple studies highlight evidence of conflict between T. s. elegans, the alien species, and M. leprosa, the native species (e.g., [91,92]). M. leprosa avoids interaction with T. scripta [93], the alien species competes efficiently for basking areas and food under experimental and natural conditions [94][95][96][97] and can transmit diseases and parasites to the native species [98][99][100]. ...
... We found that co-occurrence in less than 50% of the sites, and 48% of the variation in their co-occurrence was explained by their biotic interaction or by variables that we did not measure (which might be few since we included a long list of local and landscape variables in our study). Thus, according to previous studies [93][94][95]102], our results suggest that M. leprosa might be displaced by T. s. elegans. This could be partly explained by a combination of differences in environmental and habitat preferences and competitive exclusion. ...
... Under controlled conditions, access to food sources for M. leprosa is severely restricted by T. s. elegans. This species has a dominant aggressive behavior that can seriously affect feeding efficiency of M. leprosa, negatively impacting on their survival or reproduction [95]. Another aspect to consider is the chemosensory responses to the presence of freshwater turtles in aquatic habitats. ...
The global degradation of wetlands is increasing their susceptibility to invasions, which is greatly determined by a niche overlap between native and invasive species. We analyze its role in regulating the coexistence of the native Mediterranean stripe-necked terrapin Mauremys leprosa and the invasive Red-eared Slider Trachemys scripta elegans in a coastal wetland. We analyzed both water chemistry and landscape attributes, using variance-partitioning analysis to isolate the variance explained by each set of variables. Then, the influence of environmental variables on species co-occurrence patterns was assessed by using latent variable models (LVM), which account for correlation between species that may be attributable to biotic interactions or missing environmental covariates. The species showed a very low niche overlap, with clear differences in their response to environmental and landscape filters. The distribution of T. s. elegans was largely explained by landscape variables, preferring uniform landscapes within the daily movement buffer, whereas at larger scales, it was associated with a high diversity of habitats of small and uniform relative sizes. A high percentage of the distribution of M. leprosa was unexplained by the measured variables and may be related to the competitive exclusion processes with T. s. elegans. The species was positively related with large patches with high perimeter values or ecotone area at medium spatial scales, and it was benefited from a marked heterogeneity in the patches’ size at larger scale. According to latent variable models, both species had wide eutrophication and salinity tolerance ranges, but they showed different environmental preferences. T. s. elegans was related to eutrophic freshwater environments, whereas M. leprosa was related to more saline and less eutrophic waters. Our results suggest that M. leprosa modifies its habitat use in order to avoid interaction with the T. s. elegans. Thus, management actions aimed at removing the invasive species from the territory and promoting habitat heterogeneity might be needed to protect M. leprosa and avoid local extinctions.
... The red-eared slider is listed as one of the 100 worst invasive alien species in the world and has been reported to compete with native freshwater turtle species worldwide, leading to the extinction of their native habitats, including Mauremys sp. [26][27][28]. The Chinese pond turtle (Mauremys reevesii) was once the most abundant freshwater turtle in China [29]. ...
... Previous studies have observed that the T. scripta elegans has a greater swimming speed and an advantage in feeding kinematics, such as shorter feeding times, compared to the M. reevesii [33,34]. These advantages may give the red-eared slider turtle a competitive edge in obtaining food and basking spots [26,28]. However, the interaction between the behavioral and fitness consequences of different personalities in invasive T. scripta elegans and native M. reevesii has not been fully studied. ...
Animal personalities play a crucial role in invasion dynamics during alien species invasions. The behavioral strategies adopted by native species varied among personalities when facing an invasion by alien species, just as the invasive species exhibited variations in behavior strategies across different personalities during the invasion process. However, the effects of personality interactions between native species and invasive species on behavior and growth are rarely illustrated. We used the globally invasive freshwater turtle Trachemys scripta elegans and the native freshwater turtle Mauremys reevesii to investigate how the personality combinations of native and invasive turtles would impact the foraging strategy and growth of both species. We found that M. reevesii exhibited bolder and more exploratory personalities than T. scripta elegans. The foraging strategy of M. reevesii was mainly affected by the personality of T. scripta elegans, while the foraging strategy of T. scripta elegans was influenced by both their own personality and M. reevesii's personality. In addition, we did not found that the personality combination would affect the growth of either T. scripta elegans or M. reevesii. Difference in foraging strategy may be due to the competitive advantage of invasive species and variations in the exploration-exploitation foraging strategy among different personalities. Overall, our results reveal the mechanisms of personality interaction effects on the foraging behavior of both native and invasive species during alien species invasion and provide empirical evidence to help understand the effects of personality in invasion dynamics.
... Native freshwater turtles avoid areas with red-eared slider chemical secretions (Polo-Cavia et al., 2009;2014). Red-eared sliders are more aggressive and dominant, compete for food and basking places (Polo-Cavia et al., 2011;2014) and occupy the best habitats (Franch i Quintana et al., 2007). This competition for basking places negatively affects native freshwater turtle's survival (Pérez-Santigosa et al., 2006. ...
... Competition with the red-eared slider could show a higher sensitivity of European pond turtle, experimentally demonstrated in terms of survival and basking (Cadi and Joly, 2003;. Even though, the red-eared slider also competes with the Mediterranean pond turtle (Polo-Cavia et al., 2011;2014), displacing it to the worst habitats as they have higher reproductive potential, compete for basking places and food and the Mediterranean pond turtle avoids the red-eared slider's chemical secretions (Franch i Quintana et al., 2007;Polo-Cavia et al., 2009;2014). The higher sensitivity of the European pond turtle towards the red-eared slider could be due the reason of its decrease and the stability of the Mediterranean pond turtle when living together in other studied southern Iberian lagoons (Pérez-Santigosa et al., 2006). ...
RESUMEN El galápago de Florida: una amenaza para los galápagos autóctonos en un humedal continental del noreste ibérico. Analizamos los cambios en la estructura y la dinámica de las poblaciones entre 2004 y 2015 de dos galápagos autóctonos, el galápago leproso (Mauremys leprosa) y el galápago europeo (Emys orbicularis), que conviven con la especie exótica invasora Trachemys scripta elegans en la Reserva Natural Dirigida de Los Sotos y Galachos del Ebro, un humedal continental del noreste ibérico. Se extrajeron 206 galápagos de Florida. Sin embargo, a pesar del esfuerzo de extracción, sus capturas se mantuvieron constantes en el tiempo. El galápa-go de Florida se reproduce en la naturaleza y prevalecen las hembras de gran tamaño, que podrían provenir en parte de cautividad. Las capturas de galá-pago leproso fueron aumentando: su estimación poblacional pasó de 36 a 90 ejemplares, manteniendo una proporción equilibrada de sexos y un predo-minio de ejemplares grandes. La estimación de galápago europeo se mantuvo en el tiempo (28 ejemplares). La proporción de ejemplares pequeños (juveni-les) fue baja (8,8 % y 10,4 % respectivamente) en los galápagos autóctonos y mucho mayor (24,1 %) en el galápago de Florida, probablemente debido a LUCAS MALLADA, 24 (2022) su mayor tasa de reproducción. El seguimiento de las tres especies y la extracción de la especie exótica deben continuar para garantizar la viabili-dad de los galápagos autóctonos y se deben desarrollar campañas de educa-ción ambiental para evitar la liberación de nuevos galápagos exóticos en la naturaleza. PALABRAS CLAVE Trachemys scripta. Emys orbicularis. Mauremys leprosa. Competición. Especies invasivas. Reserva Natural Dirigida de Los Sotos y Galachos del Ebro. Noreste ibérico (España). ABSTRACT We analysed (2004-2015) the changes in population structure and dynamics of two native freshwater turtles-the Mediterranean pond turtle (Mauremys leprosa Schweigger, 1812) and the European pond turtle (Emys orbicularis L., 1758)-and the invasive American red-eared slider Trachemys scripta in the Ebro Sotos and Galachos Managed Natural Reserve, a continental wetland in NE Iberia. Two hundred and six red-eared sliders were removed. In spite of removal efforts, captures still do not decrease in time, reproduction in the wild occurs and large body females, possibly some of them coming possibly coming from captivity, prevail. Captures of Mediterranean pond turtle increases in time, its population estimate increased from 36 to 90, has a balanced adult sex ratio and large animals predominate. Estimation of European pond turtle stays in time (28 specimens). Native freshwater turtles have few small (juveniles) specimens and red-eared slider more than double them, probably due to its higher reproduction rate. The monitoring of the three species and the removal of the red-eared slider must continue to ensure native freshwater pond turtles viability. Environmental education campaigns should be developed to avoid the release of new red-eared sliders in the wild.
... In a successful invasion scenario of T. dorbigni in congener areas, the phylogenetic proximity between Trachemys species suggests that their hybridisation could occur [73,74]. In addition, sliders are considered highly competitive and aggressive turtles in their interactions [75,76]. Competition for food, and nesting and basking sites displaces native turtle species from the most suitable places for thermoregulation and where resources are most profitable [75,77]. ...
... In addition, sliders are considered highly competitive and aggressive turtles in their interactions [75,76]. Competition for food, and nesting and basking sites displaces native turtle species from the most suitable places for thermoregulation and where resources are most profitable [75,77]. Competitive displacement, together with hybridisation, can alter population structure and endanger the survival of native populations, decreasing reproductive success, and increasing mortality rates [70,78]. ...
Human activities have been changing the global biogeographic patterns by the introductions of invasive species. For reptiles, the invasion rate increase of non-native species is remarkably related to the pet trade, especially for freshwater turtles. Here we estimated the invasive potential of the South American turtle Trachemys dorbigni in the Americas using a combination of climatic and human activity variables. We built species distribution models based on data from the native and invasive ranges, using the ensemble model from five different algorithms (GAM, MAXENT, BRT, RF and GBM). We compared the two models’ performance and predictions, one calibrated with only climatic variables (climate-driven), and the second also included a descriptive variable of human activity (climate plus human-driven). Suitable areas for T. dorbigni covered occurrence areas of its congeners and highly diversified ecoregions, such as the eastern USA, the islands of Central America, and the south eastern and eastern Brazilian coast. Our results indicate that human activities allow T. dorbigni to establish populations outside of its original climatic niche. Including human activity variables proved fundamental to refining the results to identify more susceptible areas to invasion and to allow the efficient targeting of prevention measures. Finally, we suggested a set of actions to prevent T. dorbigni becoming a highly impacting species in the areas identified as more prone to its invasion.
... Ces traits sont souvent associés à la dispersion, à la reproduction (Deacon et al., 2011), ou au comportement des individus invasifs (Sol et al., 2002;Suarez et al., 2005;Juette et al., 2014). Les individus invasifs sont également souvent caractérisés par une meilleure acquisition des ressources (Polo-Cavia et al., 2011;Mathakutha et al., 2019), ainsi qu'un régime alimentaire plutôt généraliste et une plus grande tolérance aux conditions abiotiques (Moyle & Marchetti, 2006). ...
... body size, defense structures; Garvey & Stein, 1993;Smith & Knapp, 2014)) or behavioral (e.g. aggressiveness; Pintor et al., 2008;Polo-Cavia et al., 2011) response traits are major in defining reproduction success, predatory defense or dominance of invasive individuals in recipient ecosystems. Invasive generalist consumers can directly impact food webs at multiple trophic levels and affect community dynamics, in comparison with specialized individuals (Olden et al., 2004;Layman & Allgeier, 2012;Schmitt et al., 2019). ...
Intraspecific variability is now recognized for its importance on ecosystem functioning. In the context of biological invasions, which can strongly impact ecological processes, it is of high importance to understand the determinants and the patterns of genetic and phenotypic variability to fully apprehend the consequences of invasive individuals on recipient ecosystems. We demonstrated a high variability among and within populations of two crayfish species, Procambarus clarkii and Faxonius limosus, with distinct life-history traits and colonization histories in a narrow-invaded area. We highlighted that colonization history and environmental conditions were the main drivers of the contrasting patterns of genetic and phenotypic variability between the two species. Genetic analyses provided a great inference of local invasion pathways for P. clarkii, which had a great genetic variability, compared to F. limosus for which the local invasion pathways were more cryptic. We found that neutral and adaptive processes shaped the phenotypic variability of the two species in differing proportions. Then, we demonstrated the existence of a stable resource polymorphism along the benthic littoral-pelagic axis within populations of P. clarkii, suggesting that invaders could have contrasting impacts on ecosystem functioning between littoral and pelagic trophic chains. Finally, in an experiment context using a multi-traits approach, we demonstrated that the structure of trait covariations differed between species in a sympatric population, suggesting that P. clarkii impacts would be more predictable than F. limosus, and that P. clarkii could affect a higher range of ecological processes or impact the ecosystem functioning with a greater intensity than F. limosus. Overall, our findings stress the need to integrate intraspecific variability in the context of biological invasions to better understand their impacts on ecosystem functioning.
... Accordingly, there is an urgent requirement to examine the potential ecological effects of turtle species frequently purchased as pets, especially those that currently lack invasion histories. Although a popular pet species worldwide, T. s. elegans has been shown to negatively impact the growth of native turtles, and may compete for food and basking habitat with natives (Teillac-Deschamps et al. 2009;Polo-Cavia et al. 2011;Pearson et al. 2015). In Europe, T. s. elegans negatively impacts native turtle species, such as the European pond turtle (Emys orbicularis galloitalica Fritz 1995) and Spanish terrapin (Mauremys leprosa (Schweiger 1812 )) through both exploitative and interference competition (Cadi and Joly 2003). ...
... Elsewhere in Europe and around the World, non-native turtles have adversely affected native turtle species through competitive interactions (e.g., Cadi and Joly 2003). Indeed, on the Iberian Peninsula, aggressive and competitive interactions with invaders are thought to be a major cause of displacement of native Spanish turtles (Polo-Cavia et al. 2011). Hybridisation between turtle species poses a further threat to native populations when in contact with invaders (Parham et al. 2013), potentially bolstering effects related to interference and exploitative competition. ...
The poorly-regulated pet trade is a major source of potential invasive species, with deliberate release often resulting in introductions of non-native species without invasion histories. Predicting the potential impacts of species with no invasion history is particularly difficult. Functional responses (FRs; resource use as a function of resource density) have proven useful in the quantification of ecological impacts of invasive species, and may be used to screen likely impacts of species which lack invasion histories. Here, we used laboratory experiments to quantify the FRs of four freshwater turtles commonly traded as household pets: Trachemys scripta scripta, the yellow-bellied slider; T. s. troostii, the Cumberland slider; Sternotherus odoratus, the common musk turtle; and Kinosternon subrubrum, the Eastern mud turtle, towards representative chironomid and gammarid prey under eight densities in the presence and absence of substrate. All turtles exhibited potentially population destabilising Type II (hyperbolic) FRs towards each prey type, irrespective of the presence of substrate, characterised by high predation rates at low prey densities. Magnitudes of FRs were generally higher for T. s. scripta and T. s. troostii compared to S. odoratus and K. subrubrum. The presence of substrate reduced the magnitude of FRs towards both prey types overall, however, these effects were modest and most pronounced for the two. T. scripta subspecies. We demonstrate marked and sustained predatory impacts of non-native turtles on native prey, irrespective of benthic habitat contexts. We conclude that commonly traded turtles that lack invasion histories could precipitate substantial ecological impact, particularly in freshwater ecosystems where there are no native analogues.
... In China, T. scripta elegans can be observed in many locations from Hainan province (tropical region) to Liaoning (temperate region) and has displaced various native turtle species including the Chinese pond turtle Mauremys reevesii and M. sinensis (Ma and Shi 2017;Shen et al. 2011). The broader stress tolerance and stronger competitiveness of T. scripta elegans contribute to the successful invasion of this species Martín 2010, andMartín 2011;Zhang et al. 2023). Stephens and Wiens (2009) found that climatic niches can better explain the distribution and community structures of emydid turtles, suggesting the importance of climatic conditions in determining turtle distributions. ...
Greater thermal tolerance of invasive species benefits their survival and spread under extreme climate events, especially under global warming. Revealing the mechanisms underlying the interspecific differences in thermal tolerance between invasive and native species can help understand the invasion process and predict potential invaders. Here, we link the changes in global transcriptomics and antioxidant defense at multiple temperatures with the differences in thermal limits in the juveniles of a successful globally invasive turtle, Trachemys scripta elegans , and a native turtle in China, Mauremys reevesii . The two species show different thermal tolerances and have co‐existed in habitats with the risk of overheating. The majority of the transcriptional response to thermal stress is conserved in the two turtle species, including protein folding or DNA damage responses activated under relatively moderate thermal stress and regulation of the cell cycle and apoptosis during severe thermal stress. Greater thermal tolerance of T. scripta elegans can be associated with a more stable global transcriptome during thermal stress, except for necessary stress responses, and a broader thermal range of continuous up‐regulation of the core mechanisms promoting survival under thermal stress, mainly protein folding and negative regulation of apoptosis. Under extreme hot conditions, the opposite change trends of genes involved in survival mechanisms during thermal stress between invasive and native turtles can be due to differences in energy turnover. The present study provides insights into the mechanisms of physiological differences between invasive and native species given global transcriptional changes and helps understand successful invasion and predict potential invasive species.
... In recent decades, this ancient animal group has suffered from climate change, habitat fragmentation, and biological invasion (Stanford et al. 2020). The red-eared slider, Trachemys scripta elegans, is native to the eastern United States but is now a global invader of freshwater ecosystems in many countries, including China, and competes for food and basking sites with native species (Polo-Cavia et al. 2010;Polo-Cavia et al. 2011;Cerasoli et al. 2019). Sliders are now widely distributed in China and have overwhelmed co-occurring native freshwater turtles, such as the Chinese pond turtle Mauremys reevesii and the Chinese stripe-necked turtle M. sinensis, in density (Ma & Shi 2017). ...
Different responses or tolerance to thermal stress between invasive and native species can affect the outcome of interactions between climate change and biological invasion. However, knowledge about the physiological mechanisms that modulate the interspecific differences in thermal tolerance is limited. The present study analyzes the metabolic responses to thermal stress by the globally invasive turtle, Trachemys scripta elegans , as compared with two co‐occurring native turtle species in China, Pelodiscus sinensis and Mauremys reevesii . Changes in metabolite contents and the expression or enzyme activities of genes involved in energy sensing, glucose metabolism, lipid metabolism, and tricarboxylic acid (TCA) cycle after exposure to gradient temperatures were assessed in turtle juveniles. Invasive and native turtles showed distinct metabolic responses to thermal stress. T. scripta elegans showed greater transcriptional regulation of energy sensors than the native turtles. Enhanced anaerobic metabolism was needed by all three species under extreme heat conditions, but phosphoenolpyruvate carboxykinase and lactate dehydrogenase in the invader showed stronger upregulation or stable responses than the native species, which showed inhibition by high temperatures. These contrasts were pronounced in the muscles of the three species. Regulation of lipid metabolism was observed in both T. scripta elegans and P. sinensis but not in M. reevesii under thermal stress. Thermal stress did not inhibit the TCA cycle in turtles. Different metabolic responses to thermal stress may contribute to interspecific differences in thermal tolerance. Overall, our study further suggested the potential role of physiological differences in mediating interactions between climate change and biological invasion.
... Concentrated migration north may be more beneficial, as the areas along the coast will have higher salinities from the Atlantic Ocean. Migration or displacement west could also lead to an invasive species event where diamondback terrapin intrusion causes the population decline or displacement of other species, as was the case for the red-eared slider (Trachemys scripta elegans) [31]. While the competitive ability of diamondback terrapins is unknown, an overlap in range would occur for native species such as the painted turtle (Chrysemys picta), whose similar diet and basking behavior could lead to competition for resources and space [32][33][34][35]. ...
The diamondback terrapin (Malaclemys terrapin), a brackish water turtle species native to the eastern United States, is under “special concern” in the state of New Jersey, due to decreasing habitat from development and changing climatic conditions. Diamondback terrapins reside in saline marshes and coastal wetlands and nest in sandy substrate, primarily beaches and dunes, in June and July. New Jersey is vulnerable to sea level rise, leaving diamondback terrapin habitats and nesting areas at risk of inundation under future climate scenarios, and, as the most densely populated state, subject to continual development pressures on potentially conservable land. Changing sea levels and climatic conditions will cause accretion and migration of marshes into open grassy land, yielding new potential terrapin habitats, though changing temperatures could affect the availability of male-producing nesting sites and impact potential nesting patterns. This study spatially modeled lost, gained, and changed habitat and nesting areas under sea level rise scenarios for 2050 and 2100 in New Jersey and quantified these by municipality to offer insights into potential conservable land that may mitigate these changes for the vulnerable species. The results indicate an overall decrease in potential habitat coupled with a decrease in both overall and male-producing nesting ranges.
... and the Chinese Water Dragon (Physignathus cocincinus; Mo 2019b). The establishment of populations of invasive herpetofauna raises concerns for potential ecological impacts such as competition with native species (Polo-Cavia et al. 2011) and biological impacts such as pathogen transmission (Garner et al. 2006;Liu et al. 2013;Kolby et al. 2014;Meyer et al. 2015;Zhang et al. 2022). Similarly, the live plant trade is believed responsible for the introduction of the Greenhouse Frog (Eleutherodactylus planirostris) to Hong Kong (Lee et al. 2016), while the wholesale availability of live amphibians in the local pet trade facilitates an ongoing risk of further amphibian introductions. ...
... Its advanced numerical cognition may provide an intellectual advantage over the native species and contribute to its successful spread. Understanding which cognitive abilities may promote the invasive process is a novel research direction in invasion biology [19,[30][31][32]. While most turtles learned quickly, several subjects failed the training stages. ...
The ability to discriminate relative quantities, one of the numerical competences, is considered an adaptive trait in uncertain environments. Besides humans, previous studies have reported this capacity in several non-human primates and birds. Here, we test whether red-eared sliders (Trachemys scripta elegans) can discriminate different relative quantities. Subjects were first trained to distinguish different stimuli with food reward. Then, they were tested with novel stimulus pairs to demonstrate how they distinguished the stimuli. The results show that most subjects can complete the initial training and use relative quantity rather than absolute quantity to make choices during the testing phase. This study provides behavioural evidence of relative quantity discrimination in a reptile species and suggests that such capacity may be widespread among vertebrates.
... Their slow pace of life, characterized by high potential adult survival, delayed maturity, and high fecundity, makes them particularly vulnerable to environmental change at different life history stages. Habitat destruction, alteration, and fragmentation (Gerlach 2008;Doupe et al. 2009;Usuda et al. 2012;Quesnelle et al. 2013), interactions with invasive species (Thompson 1983;Polo-Cavia et al. 2011;Pearson et al. 2015), and hybridization (Fong and Chen 2010;Xia et al. 2011;Parham et al. 2013) constitute major threats for freshwater turtles. However, pollution (Adams et al. 2016;Héritier et al. 2017;but see El Hassani et al. 2019), hook ingestion (Steen and Robinson 2017), collisions with motor vehicles (Spencer et al. 2017), and human disturbance of natural behaviors (Selman et al. 2013) can also affect natural populations. ...
... Amphibians are regarded to be especially vulnerable because this terrapin feeds on tadpoles, and the presence of chemical cues released by this predator can affect the development rate and size at metamorphosis of tadpoles (Polo-Cavia et al. 2010;Vodrážková et al. 2020). The redeared slider is more aggressive and has higher reproductive characteristics and, hence, may successfully compete with native terrapin species for food, basking sites and, possibly, egg-laying places (Cadi and Joly 2003;Perez-Santigosa et al. 2008;Pérez-Santigosa et al. 2011;Polo-Cavia et al. 2011;Pearson et al. 2015). Experimental studies have confirmed a higher mortality of native European pond terrapin in the presence of the invasive red-eared slider . ...
The North American terrapin, the red-eared slider, has globally recognized invasive status. We built a new extensive database using our own original and literature data on the ecology of this reptile, representing information on 1477 water bodies throughout Eurasia over the last 50 years. The analysis reveals regions of
earliest introductions and long-term spatio-temporal dynamics of the expansion covering now 68 Eurasian countries, including eight countries reported here for the first time. We established also long-term trends in terms of numbers of terrapins per aquatic site, habitat occupation, and reproduction success. Our investigation has revealed differences in the ecology of the red-eared slider in different parts of Eurasia. The most prominent expression of diverse signs of invasion success (higher portion of inhabited natural water bodies, higher number of individuals per water body, successful overwintering, occurrence of juvenile individuals, successful reproduction, and establishment of populations) are typical for Europe, West Asia
and East Asia and tend to be restricted to coastal regions and islands. Reproduction records coincide well with the predicted potential range based on climatic requirements but records of successful wintering have a wider distribution. This invader provides an excellent and possibly unique (among animals)
example of wide alien distribution, without the establishment of reproducing populations, but through the recruitment of new individuals to rising pseudo populations due to additional releases. Therefore, alongside the potential reproduction range, a cost-effective strategy for population control must take in
account the geographical area of successful wintering
... Further, if a species exhibits greater inherent aggressiveness than a heterospecific this can also translate to a competitive advantage [15][16][17]. Aggressive encounters between invasive and native species are often asymmetric since invaders are often more inherently aggressive than natives [18][19][20][21] or possess competitively advantageous traits such as larger weaponry [22][23][24]. In some instances, greater relative aggressiveness of an invasive species can even overcome invasive-native size differences [25]. ...
Simple Summary
Aggressive invasive species can outcompete native species in contests over resources, which can lead to the exclusion of a native species by the invader. Invasive freshwater crayfish are often more aggressive than their native counterparts, however contests between invasive and native crayfish are typically investigated under laboratory conditions and are rarely examined in a natural setting. We used a baited underwater camera in a stream located in New South Wales, Australia to examine behavioural interactions between an invasive crayfish and a critically endangered native crayfish to determine which species was dominant. We found the native species dominant over the invader when larger, however when the species were size-matched the dominance of the native was lost and neither species exhibited a significant pattern of dominance. This outcome indicates the invasive crayfish represents a threat to the native since it may be able to outcompete the native over resources. Further, this outcome contrasts to previous laboratory findings, highlighting the importance of field observations in establishing the extent of impact an invader may be having on a native species.
Abstract
Competitive behavioural interactions between invasive and native freshwater crayfish are recognised as a key underlying mechanism behind the displacement of natives by invaders. However, in situ investigations into behavioural interactions between invasive and native crayfish are scarce. In Australian freshwater systems, the invasive Cherax destructor has spread into the ranges of many native Euastacus species, including the critically endangered Euastacus dharawalus. Staged contests between the two species in a laboratory setting found E. dharawalus to be the dominant competitor, however, this has yet to be corroborated in situ. Here, we used baited remote underwater video (BRUV) to examine in situ intra- and inter-specific behavioural interactions between E. dharawalus and C. destructor. We sought to evaluate patterns of dominance and differential contest dynamics between the species to provide indications of competition between the two species. We found E. dharawalus to be dominant over C. destructor based on pooled interspecific interaction data and size-grouped interactions where C. destructor was the smaller opponent. Alarmingly, however, when C. destructor was within a 10% size difference the dominance of E. dharawalus was lost, contrasting with the outcomes of the laboratory-staged study. In addition, we report that small C. destructor initiated significantly more contests than larger conspecifics and larger E. dharawalus, a pattern that was not observed in smaller E. dharawalus. Further, intraspecific interactions between C. destructor were significantly longer in duration than intraspecific interactions between E. dharawalus, indicating a willingness to continue fighting. Concerningly, these outcomes point towards inherent and greater aggressiveness in C. destructor relative to E. dharawalus and that only larger E. dharawalus hold a competitive advantage over C. destructor. Therefore, we conclude that C. destructor represents a substantial threat to E. dharawalus through competitive behavioural interactions. Further, due to the disparity between our findings and those produced from laboratory-staged contests, we recommend the use of in situ studies when determining the behavioural impacts of invasive crayfish on natives.
... Introduced or established, red-eared sliders can have large negative impact on native terrapin populations, mainly through a competition for food, basking places and breeding sites (Arvy & Servan 1998. There are also documented cases of introduced terrapins behaving aggressively towards native terrapins (Polo-Cavia et al. 2011). The substantial number of aggressive and large introduced terrapins could lead to competitive displacement of native terrapins from a relatively small lake. ...
Two allochthonous species of terrapins, Trachemys scripta (Thunberg in Schoepff, 1792), represented by individuals of the subspecies T. s. scripta and T. s. elegans (Wied-Neuwied, 1839), and the potentially invasive Pseudemys floridana (Le Conte, 1830), are recorded in the natural habitat Lake Mavrobara on the Kassandra Peninsula (Chalkidiki, Central Macedonia, Greece). The subspecies of Trachemys scripta have already been documented in various localities in Greece, with cases of possible but unconfirmed reproduction. Pseudemys floridana has not been previously recorded in Greece and this paper presents the first documented record for the country.
... Consequently, there have been extensive studies investigating the extent and status of invasive populations, their impacts, management options, and associated issues (McKee et al., 2020;Dueñas et al., 2021). Environmental impacts of invasive fauna most commonly reported include alteration of vegetation assemblages (Dunham and Mikheyev, 2010;Wilson et al., 2018), dispersal of weed species (Nimmo and Miller, 2007;Mo, 2015), predation pressure on native fauna (Parsons et al., 2020;Hamer et al., 2021), competition with and even displacement of native fauna (Polo-Cavia et al., 2011), and disease transmission (Meyer et al., 2015). There are also social and economic impacts such as agricultural losses (McKee et al., 2020;Pozebon et al., 2020), stakeholder conflicts over management strategies and policies (Carter et al., 2021), and costs associated with managing invasive populations (Cuthbert et al., 2021). ...
This study investigated the frequency and distribution of reports of free-living green iguanas (Iguana iguana), a Neotropical lizard, in Hong Kong. We found 44 reports of I. iguana, of which 93% were removed from the wild. Thirty-nine reports were records kept by one non-government organization, one report from a government agency, and four reports from community members. Reports were sporadic between 2002 and 2011, but have occurred in every calendar year since 2012, predominately during March, July and October. Report locations were distributed broadly across 16 administrative districts, including heavily developed city areas, indicative of released or escaped pets being the source. Although there was evidence of two individuals living in one locality, we found no major concentrations of reports to indicate established populations. Nevertheless, these data should not be assumed benign since some established populations of I. iguana elsewhere have only become evident following prolonged periods of sporadic reports. It is therefore plausible that emerging reports in Hong Kong may represent a contemporary invasion presently under way. Public reporting of I. iguana plays an important role in preventative invasive species management. However, we also found cases where I. iguana reported as free-living were more likely the same captive I. iguana, highlighting potential errors with community science.
... These practices allow the re-setting of spontaneous successions and increase significantly macrophyte and invertebrate diversity compared to unmanaged ponds (Sayer et al. 2012). The control of fish and invasive species can also be crucial to limit both predation of the native fauna and damages on native vegetation (Polo-cavia et al. 2011;Lemmens et al. 2013;Twardochleb et al. 2013). In meadow ponds, cattle grazing and trampling destroy banks and aquatic vegetation, and often lead to an increase in nutrient load and turbidity (Bagella et al. 2010;Harrison et al. 2017). ...
Ponds are lentic waterbodies with a high conservation value for biodiversity that have long been overlooked by management policies. Recent initiatives aimed to promote the conservation of these ecosystems by restoring or creating new ponds throughout Europe. Therefore, studying responses of aquatic invertebrates to local pond characteristics and connectivity between them is determinant to understand community dynamics and colonization processes of these scattered ecosystems. We studied larval communities of odonates in 20 created or restored ponds to assess their colonization during the first 2 or 3 years. Community dynamics in relation to pond vegetation, landscape context and connectivity with other ponds were also investigated. No difference in species richness was found between restored and created ponds. Most species colonized the ponds during the first year, but a different pattern in colonization was observed between Anisoptera and Zygoptera. Community composition was related to the landscape context of ponds and the time since pond creation or restoration. Abundances were positively related to pond connectivity, especially in the suborder Zygoptera. No relationship was found between vegetation and Anisopteran larvae, while Zygoptera seem more sensible to the vegetation structure due to their endophytic oviposition. This work confirms the high colonization capacity of odonates and shows that creation of new ponds could be as efficient as pond restoration to enhance the conservation of freshwater species. It also highlights that landscape characteristics and connectivity between ponds are determinant to support higher abundances and a posteriori increase population viability at the landscape scale.
... In contrast, painted turtles did not appear to strongly benefit from lower ecological integrity and are also not a prominent invasive species, despite also being common in the pet trade (Hohn, 2003;Telecky, 2001). Interestingly, red-eared sliders typically achieve much higher densities than painted turtles in sympatric areas Dreslik et al., 2005), indicating red-eared sliders may be competitively dominant (Lindeman, 1999;Polo-Cavia et al., 2011). ...
Anthropogenic land use changes have broad impacts on biological diversity, often resulting in shifts in community composition. While many studies have documented negative impacts on occurrence and abundance of species, less attention has been given to native species that potentially benefit from anthropogenic land use changes. For many species reaching high densities in human‐dominated landscapes, it is unclear whether these environments represent higher quality habitat than more natural environments. We examined the influence of landscape ecological integrity on relative abundance and body condition of two native generalist freshwater turtle species that are prevalent in anthropogenic systems, the painted turtle (Chrysemys picta) and red‐eared slider (Trachemys scripta elegans). Relative abundance was negatively associated with ecological integrity for both species, but the relationship was not strongly supported for painted turtles. Body condition was positively associated with ecological integrity for painted turtles, with no strong association for red‐eared sliders. Our study suggests that both species benefitted at the population level from reduced ecological integrity, but individual‐level habitat quality was reduced for painted turtles. The differing responses between these two habitat generalists could partially explain why red‐eared sliders have become a widespread exotic invasive species, while painted turtles have not.
... American pond sliders (Trachemys scripta) are among the most common pet turtles all over the world since the 1970s, but as a consequence of their frequent release in the wild, they are considered invasive alien species in many countries. With well-established populations outside their native distribution [1][2][3][4], they pose a threat for native species [5][6][7][8][9][10][11] and possible risks for domestic animals and human health [12][13][14]. For these reasons, T. scripta is listed among the 100 most invasive species by the International Union for Conservation of Nature (IUCN) [15], and its breeding and commerce have been recently prohibited inside the European Union, with Regulations (EU) 1143/2014 and 1141/2016, leading to the necessity for means of population control. ...
Simple Summary
North American pond sliders (Trachemys scripta) are invasive alien species that, following the release of pet specimens in the wild over the decades, have established breeding populations outside their native habitat, with detrimental effects on local biodiversity. Their commerce and breeding have been recently banned in the European Union, and national programs are being introduced by Union Members to eradicate and control their presence. Among other means of population control, the use of long-acting drugs for chemically induced infertility could be a promising tool to prevent the reproduction of these animals. Efficacy of single and double intramuscular deslorelin acetate implants was investigated during a one-season follow-up: plasmatic sexual hormones concentration and morphometric evaluation of ovarian activity by computed tomography were performed about every 30 days to detect the differences between the control group (no implant), single-implant group, and double-implant group. Results show no inhibition of reproductive activity for the ongoing reproductive season, but suggest possible infertility starting from the following season.
Abstract
The use of long-acting gonadotropin-releasing hormone (GnRH) agonists to suppress fertility has been poorly investigated in reptiles, and the few available studies show inconsistent results. The efficacy of single and double intramuscular 4.7 mg deslorelin acetate implants in captive pond sliders (Trachemys scripta) was investigated, with 20 animals divided into three groups: a single-implant group (6 animals), a double-implant group (6 animals), and a control group (no implant). During one reproductive season (March to October), plasmatic concentration of sexual hormones (estradiol, progesterone, and testosterone) and ovarian morphometric activity via computed tomography were monitored about every 30 days. A significative decrease in the number of phase II ovarian follicles was detected in the double-implant group compared with the control group, but no significant difference was noted in the number of phase III and phase IV follicles, egg production, and plasmatic concentration of sexual hormones. Results show that neither a single nor a double deslorelin acetate implant can successfully inhibit reproduction in female pond sliders during the ongoing season, but the lower number of phase II follicles in the double-implant group can possibly be associated with reduced fertility in the following seasons.
... On days with new enrichment, Psp1M displayed significantly less escape behavior, while Psc3M displayed significantly more escape behavior, possibly associated with its higher level of interest in the colored objects than other turtles, and Trs3M and Trt1M were significantly more aggressive, suggesting food-related or color-induced sexual motivation (Brejcha & Kleisner, 2016), as both showed more interest in red and yellow objects (Thomson, unpublished observations). Trachemys scripta are environmentally aggressive turtles, who threaten and bite during competition for food (Polo-Cavia, Lopez & Martin, 2011). Trs3M and Trt1M were also the most melanistic of the males at the TAQ, and melanistic males engage in aggressive courtship more frequently than nonmelanistic ones (Thomas, 2002). ...
The effect of environmental enrichment on the behavior and welfare in captivity of reptiles and of freshwater turtles in particular, which are popular aquarium and pet species, is very little studied compared to other taxa. We carried out a small scale case‐study on the effect of colored object enrichment, with and without fish scent, on the behavior of a group of 15 cooters (Pseudemys sp.) and sliders (Trachemys scripta ssp.) on display at a public aquarium. The new enrichment aimed to reduce the escape behavior (interaction with transparent boundaries) and increase exploration and random swimming. We used simultaneous recording of behavior at whole group level and for focal individually‐marked turtles. The escape behavior decreased on days with new enrichment before feeding at whole group level and for the focal turtles overall, in spite of the relatively low interest in the colored objects. Fish‐scented objects attracted significantly more interest. Random swimming, enrichment focus, aggression and submission increased significantly, and basking decreased significantly at whole group level before feeding, with smaller differences after feeding. There were large differences between individual turtles with respect to activity budgets and changes in behavior on days with new enrichment, with both increases and decreases seen in escape behavior, aggression, and levels of activity. Our outcomes suggested that introducing new colored objects with food scent may be beneficial for reducing escape behavior in captive freshwater turtles. However, careful monitoring of effects at individual level and much larger scale investigations, including postenrichment periods, are needed.
Research Highlights
• The presence of colored objects reduced the escape behavior of freshwater turtles, mainly before feeding.
• There was more interest when the new objects were fish‐scented.
• There were differences in behavior and response to enrichment at individual level.
... Trachemys scripta have some advantages that potentially allow them to displace native chelonians: e.g. better thermoregulatory abilities (Polo-Cavia et al. 2012), more competitive behaviour when feeding (Polo-Cavia et al. 2010) and utilising basking sites (Cadi & Joly 1999, 2004. While at present there is no evidence that T. scripta in Bulgaria displace either E. orbicularis or M. rivulata, the fact that the number of new registered localities is constantly increasing, is of great concern. ...
Since its appearance in pet stores in Bulgaria in the 1990s, the pond slider Trachemys scripta has been released at multiple localities across the country, but this process has been subject to limited scientific attention. Here, we update the distribution of this invasive alien species by adding 17 new squares to the previously published 30 of the 10×10 UTM grid. All three subspecies are present in the country, including a subadult T. s. troostii observed in 2018 at a single locality in Rupite Area, southwestern Bulgaria. More importantly, we report observations of hatchlings of T. s. elegans from two consecutive years in Rupite Area and of two subadults at Velyov Vir (Ropotamo River, Black Sea coast), strongly suggesting successful breeding in the wild. Furthermore, we provide the first national ecological niche model for T. scripta, concluding that large potentially suitable areas exist throughout the country, especially at low altitudes. We discuss similarities in the climatic conditions between the native range and Bulgaria, further suggesting that the species could likely survive and potentially reproduce across the country.
... T. scripta elegans turtles are known for the ability to tolerate long periods of fasting in different ecological contexts, as well as exhibit marked metabolic responses after food intake (Secor & Diamond, 1999). As an omnivorous opportunistic species, capable of ingesting relatively large amounts of food (Ernst & Barbour, 1989;Polo-Cavia et al., 2010;Secor & Diamond, 1999), the red-eared slider turtle was noticeably appropriate for this study, since we could easily manipulate the time period of food restriction and track the results on postprandial metabolic rates. ...
The postprandial period is characterized by a modification of the gastrointestinal activity after food intake, accompanied by an increase in metabolic rate, secretion of acids, and absorption of nutrients. For ectothermic vertebrates, those changes are particularly prominent given the relatively low metabolic cost and the low frequency of food uptake. However, prolonged fasting periods decrease energy reserves and may compromise the upregulation of costly processes, such as the increase in metabolic rate after resuming the meal intake. Assuming that the main source of energy needed to support such events is provided from the animal's own body reserves, our aim with this study is to test the hypothesis that the longer the period of fasting, the smaller the metabolic rate increase during the postprandial period, since lesser energy reserves trigger these increases. For this, we measured the oxygen consumption rates (V̇O2) of red‐eared slider turtles, Trachemys scripta elegans, submitted to different periods of fasting (47 and 102 days), before and after the ingestion of meals equivalent to 5% of their body masses. Despite the longer fasting period, which led to a reduction of 10.77% in the body mass of the turtles, there were no differences between the two experimental groups regarding maximum V̇O2 values after food intake (V̇O2 peak), postprandial metabolic scope, mean time to V̇O2 peak, and postprandial duration. Results indicate that 102 fasting days does not compromise aerobic metabolic increase during postprandial period and does not impair digestive process of the turtles, even with a loss of body mass.
... In addition, the importance of other resources in establishing hierarchies could be investigated, especially when limiting factors act simultaneously. For example, especially for pond turtles, the availability of basking sites, together with food supplies, could be of particular relevance [46][47][48], and their combined effect may strengthen or alter the final hierarchical structures. ...
Simple Summary
Many animal societies are organized in hierarchical structures, which are determined by behavioral interactions among individuals. However, the study of complex social relationships in reptiles, particularly in turtles, is still poorly studied and usually performed on adult individuals. We investigated the establishment of hierarchical social structures in hatchlings of the European Pond Turtle during their first year of life. We reared three small groups of turtles in a controlled environment and observed their pairwise interactions during food supply, on a daily basis for seven months. Data analysis was aimed at identifying the eventual hierarchical structures and describing their characteristics. The hatchlings started interacting at two months old and all groups established stable hierarchies after about one month of interactions. Turtles interacted by head bites, tail bites and mounts, but the effectiveness of these behaviors in establishing the rank of individuals was low. Both the interactions’ outcome and social ranks were independent from the turtles’ size. This study is first proof of the emergence of a social structure in the hatchlings of the European Pond Turtle in captivity, a condition that is often faced in ex situ conservation projects for this protected species.
Abstract
Few species of reptiles are known to establish stable social structures and among these, chelonians provided scarce and conflicting results. Moreover, studies on turtles are usually performed on adult individuals. In this study, we checked whether and when hatchlings of the European Pond Turtle (Emys orbicularis galloitalica) established stable hierarchical structures in their first year of life, whether hierarchies were stable in time and how steady they were. We also verified whether social ranks were associated to the individuals’ size. We observed dyadic interactions daily within three small groups of turtles reared in a controlled environment for seven months. After two months, the hatchlings started to interact and progressively established stable hierarchical structures. However, the effectiveness of the three types of observed aggressive behaviors in reversing social ranks was low and the resulting hierarchies were flat. We did not find a significant effect of the turtles’ size on their interactions’ outcome and hierarchy structure. Our results provide clear evidence of the development and the characteristics of social behaviors in young reptiles in captivity. This study could be a starting point for investigating social structures in wild populations.
... Thankfully due to our much colder climate, these introduced turtles are unable to breed (Beebee & Griffiths, 2000). This situation could change as our climate warms and certainly elsewhere in Europe red-eared sliders do breed and have started to compete with native turtle species (Perez-Santigosa et al., 2008;Polo-Cavia et al., 2011). In the UK, it is illegal to release turtles into the wild under the regulations of the 1981 Wildlife and Countryside Act. ...
It is important to map invasive species in order to demonstrate their rate of spread and current distribution. Most recording schemes rely on opportunistic sightings and awareness to collect and gather data. Mining data from online social media and other data sharing platforms has become more prevalent in recent years as increasing numbers of users share more information. In this study, sightings from the image sharing platform Flickr were compared with the records submitted to the national recording scheme Record Pool. This study was completed to determine whether or not there was a significant difference between these two as sources for sightings of fresh water turtles across the UK.
... Aggression often contributes strongly to success in interspecific competitive interactions (Dow 1977;Nishikawa 1987;Lailvaux et al. 2012;Suwanvecho and Brockelman 2012;Grether et al. 2013) and is consistently associated with successful invasive species of many taxa, including fish (e.g., Almeida et al. 2014), birds (e.g., Baker et al. 2014), turtles (e.g., Polo-Cavia et al. 2011), mammals (e.g., Hayes et al. 2012), and lizards (e.g., Cole et al. 2005;Michelangeli et al. 2017). The benefits of aggressive traits during invader dispersal (Duckworth and Badyaev 2007;Pintor et al. 2008;Hudina et al. 2014;Michelangeli et al. 2017), in driving expansion from the core population (Hudina et al. 2015), and facilitating interference competition (Bolger and Case 1992) are welldocumented. ...
Invasive species are implicated in native species declines globally, but predicting the effect of specific invaders on a given native species remains difficult. Many successful invaders are highly aggressive, whereas others are not. The highly successful invasive Asian house gecko, Hemidactylus frenatus, has achieved a pantropical distribution. We investigated direct interactions between H. frenatus and a sympatric native Australian house gecko (Gehyra dubia) to determine the strength and nature of aggressive exclusion and which species may be competitively superior. Intraspecific aggression was strong in the native, and individuals were more aggressive as residents than as intruders, suggesting this species shows site defence. In contrast, the invasive species displayed little aggression in intraspecific encounters. Overall, residents of the native species were more aggressive than residents of the invasive species. Aggression in the native species was influenced by the degree of aggression of the intruding gecko, but not by the species of intruder. Aggression from invasive residents was low and was not influenced by either the intruder's species or their behavior. Our study suggests that native Australian house geckos (G. dubia) are unlikely to be directly displaced by invasive H. frenatus, but rather that this native gecko will aggressively defend its resources when necessary. In this case, the tolerance of the invasive species for others in close proximity may contribute to its success.
First data on the cohabitation of the European Pond Turtle, Emys orbicularis, and Red-eared Slider, Trachemys scripta elegans, in the environment of a small isolated pond called Saura, located on the Mangyshlak Peninsula (Western Kazakhstan) are presented. A very small but stable population (no fewer than 20 individuals) of the Pond Turtle has been known in Saura since at least the middle of the last century. Single individuals of the Red-eared Slider were recorded in the pond in 2020 and currently at least 10–12 individuals of different ages live in the pond. The first data collected on the daily activity and behavior of the turtles show that there is not yet much competition between the species. The co-occurrence of two related turtles in a small water body is interesting from the point of view of interactions between invasive and native species. Further monitoring is essential to study this phenomenon thoroughly.
Urbanization may significantly impact wild population dynamics, even in protected green spaces. From 2016 to 2018, we accessed an assemblage of freshwater turtles isolated in an urban remnant of the Atlantic Forest, southern Brazil. We captured turtles by active search, hookless fishing, and funnel trap, and we marked them individually. Using a capture-mark-recapture method, we estimated population density, and movement, including home range size and habitat selection. Home ranges were estimated using the 100% minimum convex polygon method and habitat selections through eigenanalysis. We captured 41 specimens of Phrynops geoffroanus (Schweigger, 1812), 35 Trachemys dorbigni (Duméril & Bibron, 1835), and 20 Trachemys scripta elegans (Wied-Neuwied, 1839). The invasive T. dorbigni showed the highest density (1.72 individual/ha), followed by the native P. geoffroanus (1.36 individual/ha) and the invasive T. scripta elegans (0.87 individual/ha). Home range sizes for P. geoffroanus and T. dorbigni ranged between 0.04-0.48 ha, with the latter species covering the longest distance (525.8 m). All three species showed a preference for habitats influenced by human presence (walkways). Our findings highlight the anthropic influence on the movement of the freshwater turtle assemblage and underscore the need for enhanced protection of native species and control of invasive turtles. This study provides essential baseline data for future researches and management of urban areas.
KEYWORDS: Anthropic pressure; chelonians; hotspot; habitat selection; home range; invasive alien species
Invasive species are a growing global concern. Modern transportation and the pet trade are facilitating the spread of invasive species. In particular, the global trade of freshwater turtles remains prevalent, with a significant emphasis on their utilization as pets. Aligning with other parts of the world, many recent studies reported a number of alien turtle species in the wild in Korea. However, knowledge of their local establishment and natural breeding is still very limited. In the current study, we report the first natural breeding of Mauremys sinensis in the wild in South Korea. The external features of the observed individual and egg characteristics confirmed its identification. The individual took around 70 minutes to build the nest, lay eggs, and cover up the nest with the soil that it dug from the nest. We recorded a clutch size of ten eggs. The rigid-shelled eggs had an average elongation of 1.82 mm, smaller than M. reevesii. Thus, we confirm the natural breeding and local establishment of M. sinensis in South Korea. Considering previous reports, this finding is significant for understanding both potential competition and putative hybridization with the native species, especially M. reevesii, the endangered native freshwater turtle species in Korea.
Urbanization is a significant driver of the global biodiversity crisis. Turtles are particularly impacted by urbanization because of the vulnerability of riparian habitats to habitat loss and road mortality. Behaviour plays a crucial role in determining the success of urban animals. Behavioural responses to urbanization, however, are rarely studied in turtles even though many turtles are at‐risk and sometimes live in urban areas. Therefore, we evaluated behavioural changes in painted turtles ( Chrysemys picta ) living in wetlands surrounded by a gradient of urbanization. We tested the consistency of painted turtle behaviour in the laboratory and examined the behaviour of painted turtles from 24 wetland sites across an urbanization gradient in Ottawa, Ontario, Canada. We assessed: (i) aggression by measuring the number of active defensive behaviours the turtles performed in response to handling, (ii) boldness by measuring the amount of time the turtles took to emerge from their shells and move from their initial locations in a circular arena and (iii) activity by measuring the amount of time the turtles spent moving in the same circular arena. We found that all behaviours were consistent in the laboratory. We also found that as the level of urbanization increased, turtles were more aggressive and bolder. Urbanization affects painted turtle behaviour, but further research is required to understand the mechanisms responsible and the conservation implications.
Many freshwater turtle species have spread beyond their natural distributions through human agency, but introduced populations can be difficult to differentiate from natural ones. The occurrence of an Australian freshwater turtle, Emydura macquarii, in the Greater Sydney region, Australia's most populous urban and peri-urban area, has alternatively been assumed to be natural or deduced to be due to anthropogenic introduction. I apply multiple lines of evidence to show that the occurrence of E. macquarii in the Sydney region is not natural and that the species has proliferated and spread there much more than the notoriously invasive red-eared slider turtle, Trachemys scripta elegans. The E. macquarii population of the Sydney region is highly diverse morphologically, with individuals variously resembling E. macquarii from Queensland, the north coast of New South Wales, and the Murray–Darling Basin. Better understanding is needed of the population genetics of E. macquarii in the Sydney region, the interactions among the region's native and introduced turtles, and the impacts of E. macquarii on biota other than turtles.
Human activities affect terrestrial and aquatic habitats leading to changes at both individual and population levels in wild animal species. In this study, we investigated the phenotype and demographics of the Mediterranean pond turtle Mauremys leprosa (Schweigger, 1812) in contrasted environments of Southern France: two peri-urban rivers receiving effluents from wastewater treatment plants (WWTP), and another one without sewage treatment plant. Our findings revealed the presence of pesticides and pharmaceuticals in the three rivers of investigation, the highest diversities and concentrations of pollutants being found in the river subsections impacted by WWTP effluents. Principal component analysis and hierarchical clustering identified three levels of habitat quality, with different pollutant concentrations, thermal conditions, nutrient, and organic matter levels. The highest turtle densities, growth rates, and body sizes were estimated in the most disturbed habitats, suggesting potential adult benefits derived from harsh environmental conditions induced by pollution and eutrophication. Conversely, juveniles were the most abundant in the least polluted habitats, suggesting adverse effects of pollution on juvenile survival or adult reproduction. This study suggests that turtles living in polluted habitats may benefit from enhanced growth and body size, at the expense of reproductive success.
Little is known about the behavioral and cognitive traits that best predict invasion success. Evidence is mounting that cognitive performance correlates with survival and fecundity, two pivotal factors for the successful establishment of invasive populations. We assessed the quantity discrimination ability of the globally invasive red-eared slider (Trachemys scripta elegans). We further compared it to that of the native stripe-necked turtle (Mauremys sinensis), which has been previously evaluated for its superior quantity discrimination ability. Specifically, our experimental designs aimed to quantify the learning ability as numerosity pairs increased in difficulty (termed fixed numerosity tests), and the immediate response when turtles were presented with varied challenges concurrently in the same tests (termed mixed numerosity tests). Our findings reaffirm the remarkable ability of freshwater turtles to discern numerical differences as close as 9 vs 10 (ratio = 0.9), which was comparable to the stripe-necked turtle’s performance. However, the red-eared slider exhibited a moderate decrease in performance in high ratio tests, indicating a potentially enhanced cognitive capacity to adapt to novel challenges. Our experimental design is repeatable and is adaptable to a range of freshwater turtles. These findings emphasize the potential importance of cognitive research to the underlying mechanisms of successful species invasions.
SOUTH AMERICAN JOURNAL OF HERPETOLOGY
Abstract: Invasive amphibians and reptiles have historically been ignored by governments and science, especially in the Neotropics. There have been few studies related to invasive herpetofauna in Brazil, making information about this group scarce. Our aim was to review the current status of alien amphibians and reptiles with wild populations in Brazil. We compiled knowledge about the history of invasions, biological characteristics of species, and their impacts and current distributions in Brazil. In addition, we discuss management and policy actions that must be implemented for each species, especially for the most harmful ones. We found six amphibian and six reptile invasive species recorded in Brazil, in addition to four reptile species that were considered potential invaders. There are confirmed negative impacts on human health and biodiversity for two amphibians (Aquarana catesbeiana and Rhinella jimi) and two reptiles (Salvator merianae and Trachemys scripta elegans). The main routes of introduction of invasive herpetofauna in
Brazil are the pet trade and commercial production. Most invasive species are present in the Atlantic Forest and three are found only in the Fernando de
Noronha archipelago. Furthermore, most species have small and dispersed populations that allow monitoring programs for research or even eradication,
especially for island populations. Species at more advanced stages of invasion, such as A. catesbeiana and T. scripta elegans, need a national program to control populations and prevent spread. Further ecological studies are important to assess the impacts of invasive herpetofauna on Brazilian biodiversity, as is the straightforward implementation of action plans with the best techniques for the control or eradication of these populations.
Le nombre d’invasions biologiques détectées dans le monde est en constante augmentation, en raison de la mondialisation. Les écrevisses, utilisées en aquaculture et très appréciées en aquariophilie, sont une belle illustration de ce phénomène. Parmi elles, l’écrevisse bleue Cherax quadricarinatus, d’origine australienne, est une espèce phare en aquaculture, en milieu tropical. De ce fait, elle a été transloquée dans de nombreux pays à travers le monde, dont la Martinique, où elle a été introduite au début des années 2000, pour redynamiser le secteur aquacole. Vendue vivante et très appréciée par les locaux, elle a été relâchée dans les rivières et a commencé à coloniser des bassins versants entiers, sans pour autant connaître précisément sa distribution. La Martinique est un territoire insulaire, appartenant à l’un des hotspots de biodiversité les plus riches du monde et les conséquences d’une telle invasion sur l’écosystème et les communautés locales doivent être appréhendées. Le développement de la technique ADN environnemental a permis, dans un premier temps, de préciser son aire de répartition. Parmi les 90 sites inventoriés, répartis sur 53 cours d’eau (parmi les 60 permanents de Martinique), l’écrevisse a été détectée sur 23 rivières. L’étude de la diversité génétique a révélé l’existence de plusieurs haplotypes, provenant probablement de plusieurs événements d’introduction. L’analyse des isotopes stables (ici azote δ15N et carbone δ13C) de la chaine trophique, a permis de caractériser les impacts de C. quadricarinatus sur les communautés locales : il semblerait que l’écrevisse occupe une place plutôt basse dans la niche trophique, caractérisant un régime alimentaire omnivore, à tendance herbivore. Des changements ontogénétiques ont également été observés, avec une alimentation différente selon les différents stades de vie. Les comparaisons des structures de niche trophique entre les zones envahies et les zones non-envahies ont montré un impact significatif sur les espèces de crevettes autochtones, par un phénomène d’exclusion compétitive. Aux vus de sa forte propagation depuis son introduction, la lutte contre cette espèce exotique envahissante parait compliquée. La pêche intensive ne peut régler cet épineux problème d’autant plus, que le contexte écotoxicologique local rend cette pratique non recommandable. En effet, les rivières Martiniquaises sont contaminées par le chlordécone, un pesticide largement utilisé jusqu’en 1993 dans les Antilles Françaises, provoquant l’interdiction de la pêche en rivière, par arrêté préfectoral. Nos expériences menées ont montré des taux de chlordécone importants dans les tissus abdominaux des écrevisses, dépassant largement les limites maximales fixées par l’Agence Régionale de Santé. Des expériences de décontamination de ces produits de pêche ont été menées, mais ceci ne semble pas être une alternative suffisamment efficace.
This datasheet on Trachemys scripta elegans covers Identity, Overview, Distribution, Dispersal, Diagnosis, Biology & Ecology, Impacts, Uses, Prevention/Control, Further Information.
The impacts from urban areas may result in alterations in environmental characteristics and wild populations dynamics. Therefore, we aimed at assessing population size, density, home range, maximum range of movement and habitat selection of native and aliens freshwater turtles in a Brazilian urban park ( Phrynops geoffroanus- PG, Trachemys dorbigni- TD, Trachemys scripta elegans -TSE). We applied capture-mark-recapture procedures from July/2016 to August/2018. Home ranges were estimated from trap locations using a 100% minimum convex polygon (MCP) method, and habitat selections using eigenanalysis. We sampled 41 PG, 35 TD, and 20 TSE. Population size was estimated as 59 ± 7.6 (PG), 36 ± 1.4 (TD), and 20 ± 0.5 (TSE) individuals (± SE), with a density estimates of 1.36 (0.34), 1.72 (0.36), and 0.87 (0.25) individual/ha (± SE), respectively. Home ranges size ranged between 0.04 ha and 0.48 ha, the highest distance was reached by D'Orbigny's slider (525.8 m). Our results indicate that habitat preferred for all species is clearly influenced by human presence, and the turtle assemblage exhibit strategies as temporal segregation to coexist on this small, closed park. Both the presence of two established populations of invasive alien species and the changing movement of freshwater turtles reflect anthropic pressure on wild population dynamics and the lack of effectiveness of environmental policies and inspection in Brazil. The understanding that wild populations are being affected even in conservation units could be considered by the managers implement monitoring of target wild populations, control of exotic species, insertion of educational signs and actions, and control of visitors.
The Northwestern Pond Turtle (Actinemys marmorata; WPT) was once widespread throughout the Sacramento Valley and the Sacramento-San Joaquin River Delta. Much of its historical range has been converted into agricultural land, reducing and altering aquatic habitat and surrounding uplands. Red-eared Sliders (Trachemys scripta elegans; RES) have been introduced throughout much of the existing WPT range, particularly near urban centers, potentially competing with WPT for resources. Previous surveys for turtles in central California have primarily focused on rivers, lakes, and protected wetlands. Little is known about where WPT and RES occur in the vast expanses of agricultural land across the Sacramento Valley and Sacramento-San Joaquin River Delta. Using aquatic hoop nets, we surveyed 142 locations (102 irrigation canal sites, 39 wetlands, 1 tidally influenced slough) across 8 counties during the summers of 2018 and 2019. Both species were detected in agricultural habitats. Using occupancy modeling, we estimated that WPT occur at 44 (95% CRI = 3853) of our trapping sites and RES occur at 51 (4166) sampled sites. Co-occurrence of these 2 species was rare; the species were found together at only 6 sites. RES were primarily found in restored wetlands near major roads and the Sacramento metropolitan area, whereas WPT were more commonly found farther from urban areas in wider canals. Our work provides a picture of how WPT and RES occupy this modified agroecosystem that can inform future conservation efforts.
Biological invasions are one of the worst threats to biodiversity conservation, ecosystem services and functionality, and human health. However, of the high number of organisms that are transported and introduced outside their native range, only a subset of them can survive, establish and spread in the novel area, becoming invasive. What determines the ability of an alien animal species to become invasive? There is an increasing awareness that the answer to this longstanding and crucial question is highly multifactorial, with some factors already well-discerned, and some not yet elucidated. In this book chapter, we focus on developmental plasticity, the permanent change in the developmental trajectory adopted by an organism in response to gene–environment interactions. Developmental plasticity is an important adaptive response to the obvious variability of biotic and abiotic environmental conditions over time. Yet, it can also promote the invasion of novel habitats, by favouring the optimal match between individual phenotypes and the new environment, during the early steps of an invasion. By relying on the available literature and focusing on animal invasions, we analyse the adaptive advantages conferred by developmental plasticity (i) in dealing with the new biotic and abiotic environment during the stage of introduction, (ii) in terms of reproductive rate and population growth, two crucial processes for overcoming the stages of establishment and (iii) in dispersal traits promoting the spread in the new environment. We conclude that, although acknowledged in previous literature, the actual contribution of developmental plasticity to the shaping of the ideal invader might have been underrated.
• The introduction of freshwater turtle species outside their natural ranges may threaten native turtles through competition for resources such as food or basking sites, hybridization, and transmission of diseases or parasites.
• The three southern species of Australian helmeted turtles (Myuchelys bellii, Myuchelys georgesi, and Myuchelys purvisi) had no or minimal distributional overlap with the widespread Australian Macquarie turtle, Emydura macquarii, until about 30 years ago. Since that time, E. macquarii has been introduced within the ranges of all three Myuchelys spp., possibly through the release or escape of pet turtles.
• The occurrence, catch per unit effort, and population structure of E. macquarii were compared among four introduced populations within the ranges of southern Myuchelys spp. and four native populations. The aim was to provide insight into the status of the introduced populations, their likely current impact on Myuchelys spp., and their potential for future increase.
• Data analysis suggested that the introduced populations of E. macquarii are at varying stages of the invasion process and not yet severe threats to Myuchelys spp. However, continuing proliferation of introduced E. macquarii is likely, potentially placing intensifying pressure on Myuchelys populations in the long term.
• Research is needed on interactions of E. macquarii and Myuchelys spp. and their comparative competitive abilities in order to inform the difficult policy decision of whether invasive E. macquarii should be removed or controlled.
El comercio de quelonios acuáticos como animales de compañía y su eventual liberación o escape ha conllevado la detección de especies exóticas naturalizadas o formando poblaciones invasoras en ecosistemas acuáticos. La importación de Mauremys spp. exóticos implica una nueva amenaza para la conservación de los ecosistemas acuáticos, debido a su capacidad de hibridarse con la especie nativa Mauremys leprosa. En este trabajo se documentan 16 nuevos registros de ejemplares asilvestrados de los galápagos asiáticos Mauremys reevesii y Mauremys sinensis en Andalucía (sur de España). La mayor parte de ellos (13) corresponden a ambientes acuáticos artificiales asociados a áreas urbanas y el resto se encontraron en espacios naturales protegidos con poblaciones naturales de M. leprosa. Estas nuevas citas ponen de manifiesto que los nuevos taxones comercializados reproducen el patrón de venta-abandono-naturalización-invasión ya acaecido con otras especies exóticas de galápagos. El número de ejemplares de Mauremys exóticos importados en España (más de 100.000 desde 2006) sugiere que el número real de ejemplares asilvestrados podría ser bastante mayor al documentado en los trabajos publicados.
Introduced alien species can negatively affect native competitors by reducing their populations or eliminating them from ecosystems. However, studies do not always find evidence for anticipated impacts, and changes in native populations can be difficult to estimate. Interactions between the invasive American mink Neovison vison and native European polecat Mustela putorius have been studied in several countries, but the mink’s impact on polecat populations at a large spatiotemporal scale remains unclear. In the years 1995–2018, we live-trapped mink and polecats at 60 study sites in Poland, and we analysed hunting bags of mink and polecats from the years 2009–2018. During 13,766 trap-nights, we captured 905 individuals. Mink comprised 91.2% and polecats 8.8% of trapped animals. The mean mink and polecat trappability was 6 and 0.6 individuals per 100 trap-nights, respectively. At rivers, polecat and mink trappability were negatively correlated, whereas at lakes, they were not correlated. The sex ratio of trapped polecats was more skewed toward males than that of mink. Mink comprised 63.6% and polecats 36.4% of 59,831 animals killed by hunters. Over 10 years, the numbers of mink shot annually increased slightly, whereas the numbers of polecat decreased slightly. There was a positive correlation between numbers of mink and polecats shot annually. We found weak evidence that at a large spatiotemporal scale, the invasion of mink has led to a decline in polecat numbers. Although the datasets we analysed were based on large samples, they were insufficient to show evidence of competitive interactions between these two mustelids.
Trachemys scripta (Reptilia, Emydidae) is among the most widespread invasive reptiles in the world. In general, it is assumed that this species has negative effects on native aquatic turtles based on experiments conducted under controlled conditions. Here, we analysed a 7-year time series (2013-2019) of data from captures of three species of turtles (two natives and one alien) from natural populations in the northeastern Iberian Peninsula. We evaluated (i) the interspecific spatial overlap and (ii) the correlation between the scaled mass index (SMI) of the native turtles and the abundance of T. scripta, including an interaction effect between the species. The analyses revealed that T. scripta has relatively low spatial overlap with Emys orbicularis but high overlap with Mauremys leprosa. Overall, the abundance of T. scripta was not associated with significant variations in the SMI of the native species, although for the female E. orbicularis, we detected a negative trend. The analyses also indicated that the abundance of T. scripta does not have an additive effect on the SMI of other turtles, even if there is a negative effect between native species. These findings suggested that the impact of T. scripta on other turtles could be density-dependent.
This document aims to answer frequently asked questions (FAQs) on how the EU Invasive Alien Species Regulation (IAS Regulation) can support the implementation of the EU Habitats and Birds Directives (the Nature Directives) and vice versa. The document is aimed at the competent authorities responsible for implementing the IAS Regulation, and the competent authorities for the Nature Directives (including Natura 2000 site managers). It will also help land managers and landowners in Natura 2000 sites to understand what consequences the IAS Regulation might have for their land management practices, whether they are farmers, foresters, or protected area managers. The FAQ provides many examples and links to further information. An annex summarises the evidence of impacts of invasive alien species (IAS) on Natura 2000 and the species and habitats listed in the annexes of the Nature Directives, with tables featuring all the 66 IAS of Union Concern, their presence, and the current evidence of impacts (with reference lists). The FAQ guidance was a key commitment under the EU Action Plan for People, Nature and the Economy, published after the fitness check of the EU Nature Directives showed that more action is needed to speed up implementation of the nature directives.
It is available at
https://ec.europa.eu/environment/nature/natura2000/management/docs/FAQ_IAS.pdf
The red-eared slider turtle (Trachemys scripta elegans; RES) is often considered one of the world's most invasive species. Results from laboratory and mesocosm experiments suggest that introduced RES outcompete native turtles for key ecological resources, but such experiments can overestimate the strength of competition. We report on the first field experiment with a wild turtle community, involving introduced RES and a declining native species of conservation concern, the western pond turtle (Emys marmorata; WPT). Using a before/after experimental design, we show that after removing most of an introduced RES population, the remaining RES dramatically shifted their spatial basking distribution in a manner consistent with strong intraspecific competition. WPT also altered their spatial basking distribution after the RES removal, but in ways inconsistent with strong interspecific competition. However, we documented reduced levels of WPT basking post-removal, which may reflect a behavioral shift attributable to the lower density of the turtle community. WPT body condition also increased after we removed RES, consistent with either indirect or direct competition between WPT and RES and providing the first evidence that RES can compete with a native turtle in the wild. We conclude that the negative impacts on WPT basking by RES in natural contexts are more limited than suggested by experiments with captive turtles, although wild WPT do appear to compete for food with introduced RES. Our results highlight the importance of manipulative field experiments when studying biological invasions, and the potential value of RES removal as a management strategy for WPT.
Several species of amphibians and reptiles new to Poland were described recently. However, data on their origin, distribution and taxonomic status are often limited and ambiguous. Here, we summarize the current state of knowledge on these species and propose some changes to the national list of protected species. The eastern tree frog and eastern slow worm are native to Poland and should be under strict and partial protection, respectively. We recommend inclusion of these species in the regional lists of protected species until the national list is updated. The status of four other taxa (Balkan frog, toad Bufotes variabilis, common wall lizard and dice snake) is uncertain and needs further study. Until the status of the dice snake is established, it should be removed from the list of protected species.
Reviews information on relocations, repatriations, and translocations (RRT) projects involving amphibians and reptiles, examines the motives for advocating RRT strategies, and recommends biological and management criteria that should be considered prior to undertaking RRT projects. Most projects involving amphibians and reptiles have not demonstrated success as conservation techniques and should not be advocated as if they are acceptable management and mitigation practices. -from Authors
Previous field experiments indicated that the rocky intertidal starfish Pisaster ochraceus and Leptasterias hexactis compete for food. Here, the method of resource partitioning and mechanisms of competition and of coexistence are examined. Comparisons between the diets, feeding activities (high tide), and location at low tide are made for co-occurring Lep-tasterias (0.01-11.5 g wet weight) and small (0.01-11.5 g), medium (11.5-100 g), and large (100-550 g) Pisaster. These comparisons suggest that (1) there is no spatial or temporal subdivision of the habitat while feeding, (2) there is some microhabitat separation at low tide, with Leptasterias farther back both in crevices and under rocks, and (3) although the diets of the two species overlap greatly in both size and species of prey eaten, each obtains most of its energy from a different combination of prey size and species. Leptasterias obtains most of its energy from small-to medium-sized mobile prey; small Pisaster depend on small, sessile prey, and medium to large Pisaster depend on larger and more mobile prey. Thus, the food resource is divided along a combination of resource dimensions and not along a single resource "axis." Laboratory experiments indicate (1) that Pisaster is highly aggressive toward Leptasterias, using its pedicellariae to pinch the latter, and (2) the effect of this aggression is to reduce the feeding rate of Leptasterias. Field experiments confirm this result. This aggression is somewhat surprising in light of the complete spatial overlap of the competitors. Coexistence is possible because in nature the smaller seastar evidently acclimates relatively quickly to changes in Pisaster abundance. Leptasterias is not aggressive towards Pisaster, and its location at low tide suggests it avoids close contact with the larger asteroid. The primary competitive advantages of the larger asteroid thus are the ability to reach a larger size (and thus to capture "better" prey), and aggression. The competitive advantage of the smaller starfish is suggested by calculations of the number of calories of prey consumed per gram wet weight of starfish per tidal cycle. These comparisons indicate Leptasterias has a higher rate of energy intake than Pisaster. Since this advantage could conceivably give Leptasterias a great initial size advantage over small Pisaster, aggression may function to reduce the foraging time of the former. As Pisaster recruitment is low, small individuals of this species are rare. Leptasterias may coexist with Pisaster by (1) reproducing at a small size (2 g wet weight vs. 70-90 g in Pisaster) and (2) using a spatial portion of the intertidal (deeper parts of crevices) not normally utilized by Pisaster during low tide when the two species would be in closest association. Pisaster's aggressive superiority may render invasion of this system by large asteroid predators similar to Pisaster impossible.
Slider turtles, Chrysemys scripta, attain biologically and statistically significantly larger sizes on Atlantic Coast islands than do natural populations on the mainland. The sizes of individuals on these islands are comparable to those reported previously for turtles from a unique aquatic situation in a thermally altered reservoir. Higher quality diets and warmer temperatures appear to be satisfactory explanations for the island and reservoir situations.
Evaluated niche changes in European tits. In all 7 cases studied, 1 or 2 species showed a clear, divergent ecological shift in the area of sympatry. Likewise, Alatalo (1981) found a general pattern of divergence in foraging sites in mixed-species tit flocks compared with monospecific flocks. These significant tendencies toward divergent rather than convergent shifts in the presence of putative competitors cannot be explained by differences in the environment alone. The strongest evidence that interspecific competition causes niche changes comes from the observation that, within the guild, changes were found only in the species that morphologically most closely resembled the species that were absent in allopatry (weight ratio = or <1.2). -from Authors
Inter- and intra-specific interactions included open mouth gestures, biting, and 2 previously undescribed behaviors: lateral and vertical displacement. Aggression was most frequent from 0900-1000 h, at water temperatures between 30-32°C. Basking turtles avoided potentially aggressive encounters by averting faces while basking and moving away from approaching turtles. Directionality of behavioral interactions was strongly influenced by relative body size. Aggressive behavior was positively correlated with number of turtles basking, frequency of emergences, and water temperature. -from Author
Competition and its effects are difficult to demonstrate, as they vary depending on the species present and the environmental conditions in each community. We conducted laboratory and field experiments to evaluate the effects of intra- and interspecific interactions on the use of food resources and behavior of the sea stars Leptasterias polaris and Asterias vulgaris, 2 major predators in subtidal communities of the northern Gulf of St. Lawrence, We demonstrate interference (encounter) competition between the two. For both species, the presence of the other (as detected by both contact and chemical signals) decreased feeding activity and provoked behavioral changes (avoidance, decrease in percentage feeding). These effects were reversible and short-lived, and were more pronounced when there was a shortage of food and when sea stars were exposed to simulated attacks by the other species (involving pedicellarial pinching). L. polaris seemed to be the inferior competitor as (1) it switched to less profitable prey size (smaller mussels, Mytilus edulis) when A. vulgaris was present, and (2) it avoided A. vulgaris and reduced its feeding activity when food was scarce, The dominance of A. vulgaris is possibly attenuated at our study site (near its northern distributional limit) by the reduction of its fitness when water temperatures are low (most of the year) and during the winter when it migrates to deeper water, Competition for food resources seems to occur periodically (mainly summer), in localized areas (patches and beds of mussels) or when sea stars form dense aggregations in which they are likely to interact frequently, Interactions, and thus the chance of competition, are less likely at greater depths. Coexistence seems to be permitted by both the attenuation of the dominance of A. vulgaris and by the great variations in how L. polaris and A. vulgaris interact (strongly affected by variations in prey availability, sea star abundance, and in the patterns of prey use by both sea stars).
Animal species have evolved different diel activity rhythms that are of adaptive value. Theory suggests that diel temporal partitioning may facilitate co-existence between competitors and between predators and prey. However, relatively few studies demonstrate a temporal shift that is predation-or competition-induced. Recorded shifts are usually within the preferred activity phase of animal species (day or night), although there are some inversions to the opposite phase cycle. Temporal partitioning is not perceived as a common mechanism of coexistence. This rarity has been variously ascribed to theoretical considerations and to the rigidity of time-keeping mechanisms, as well as to other physiological and anatomical traits that may constrain activity patterns. Our decade-long study of spiny mice of rocky deserts demonstrates that, while different factors select for activity patterns, endogenous rhythmicity may be an evolutionary constraint.
When a species colonizes an area that it has not previously inhabited, it is called an "invasion", and it can result in the extinction of endemic species. The increase in numbers of humans travelling the world presents opportunities for invasions by organisms and the spread of diseases such as rabies and smallpox. Using the large amount of data from studies in pest control and epidemiology, it is possible to construct mathematical models that can predict which species will become invaders, which habitats are susceptible to invasion, and the biological impact. This book presents a clear and accessible introduction to the modeling of biological invasions. It demonstrates the latest theories and models, and includes data and examples from various case studies showing how these models can be applied to problems from deadly human diseases to the spread of weeds.
The present book is based on an earlier one published in Japan (in Japanese) by one of the authors (N.S.), entitled Mathematical modeling for biological invasions (University of Tokyo Press, 1992); this English edition, however, results from the collaboration between two authors. The original Japanese edition is aimed primarily at university undergraduate and graduate students, and its purpose is to introduce to them some of the pioneering works in biological invasion as well as some mathematical models developed by the authors. Necessarily, discussions on many relevant theories, field data, and their references were curtailed in favor of conciseness. For this English edition, we have included more field data, updated some theoretical results according to the latest findings, and rewritten much of the text with a wider audience, including field researchers and scholars, in mind.
The diet of red-eared turtle shifted gradually from insect to plant material with increasing plastron length, and paralleled a habitat shift from feeding sites in shallow to deep water. Basking perches used by small turtles were narrower, more steeply sloped, and located in shallower water than those used by large turtles.-from Author
Previous field experiments indicated that the rocky intertidal starfish Pisaster ochraceus and Leptasterias hexactis compete for food. Here, the method of resource partitioning and mechanisms of competition and of coexistence are examined. Comparisons between the diets, feeding activities (high tide), and location at low tide are made for co-occurring Leptasterias (0.01-11.5 g wet weight) and small (0.01-11.5 g), medium (11.5-100 g), and large (100-550 g) Pisaster. These comparisons suggest that (1) there is no spatial or temporal subdivision of the habitat while feeding, (2) there is some microhabitat separation at low tide, with Leptasterias farther back both in crevices and under rocks, and (3) although the diets of the two species overlap greatly in both size and species of prey eaten, each obtains most of its energy from a different combination of prey size and species. Leptasterias obtains most of its energy from small- to medium-sized mobile prey; small Pisaster depend on small, sessile prey, and medium to large Pisaster depend on larger and more mobile prey. Thus, the food resource is divided along a combination of resource dimensions and not along a single resource @'axis.@' Laboratory experiments indicate (1) that Pisaster is highly aggressive toward Leptasterias, using its pedicellariae to pinch the latter, and (2) the effect of this aggression is to reduce the feeding rate of Leptasterias. Field experiments confirm this result. This aggression is somewhat surprising in light of the complete spatial overlap of the competitors. Coexistence is possible because in nature the smaller seastar evidently acclimates relatively quickly to changes in Pisaster abundance. Leptasterias is not aggressive towards Pisaster, and its location at low tide suggests it avoids close contact with the larger asteroid. The primary competitive advantages of the larger asteroid thus are the ability to reach a larger size (and thus to capture @'better@' prey), and aggression. The competitive advantage of the smaller starfish is suggested by calculations of the number of calories of prey consumed per gram wet weight of starfish per tidal cycle. These comparisons indicate Leptasterias has a higher rate of energy intake than Pisaster. Since this advantage could conceivably give Leptasterias a great initial size advantage over small Pisaster, aggression may function to reduce the foraging time of the former. As Pisaster recruitment is low, small individuals of this species are rare. Leptasterias may coexist with Pisaster by (1) reproducing at a small size (2 g wet weight vs. 70-90 g in Pisaster) and (2) using a spatial portion of the intertidal (deeper parts of crevices) not normally utilized by Pisaster during low tide when the two species would be in closest association. Pisaster's aggressive superiority may render invasion of this system by large asteroid predators similar to Pisaster impossible.
Food and feeding strategies were examined in two populations of Graptemys pseudogeographica ouachitensis. Diets were determined from examination of entire digestive tracts. Mississippi River specimens are opportunistic feeders, consuming whatever foods become available to them in their barren, inorganic habitat. Diets are supplemented in high-water periods with normally terrestrial vegetation and insects which become accessible. Vegetation becomes more important in the diet as Mississippi River turtles become larger. Meredosia Lake specimens of all sizes are more restricted in diet, mainly consuming locally abundant midge larvae (Chironomidae) throughout the summer of study.
I observed 123 instances of aggression in 100.7 h among basking emydid turtles (Trachemys scripta, Pseudemys concinna, Graptemys pseudogeographica, and G. ouachitensis). No consistent Pattern occurred in heterospecific interactions with regard to outcomes. Larger turtles "won" (i.e. caused or resisted displacement) in 70% of all interactions, and initiators won 80%; in all, 61% were won by larger, initiating turtles. Larger turtles displaced smaller turtles into the water more often than the reverse. Larger turtles also elicited avoidance behaviors from smaller turtles that were not elicited from larger turtles by smaller turtles. The hypothesis that smaller turtles assess and avoid larger turtles was suggested by (1) the lower rate of initiation by smaller turtles, (2) the turning away response that was observed only in smaller turtles, and (3) the fact that smaller turtles sometimes voluntarily displaced themselves when larger turtles emerged from the water or advanced toward them on a substrate, but the reverse was not observed. Alternatively, inherent aggressiveness may be a function of body size in these species.
Enhanced growth rates and body sizes in populations of aquatic turtles (Chrysemys scripta) from thermally impacted habitats are attributed to differences in diet quality and elevated water temperatures. A dietary analysis, utilizing a stomach flushing technique, showed that turtles from a nuclear reactor cooling reservoir ingest more than twice as much protein as turtles from natural aquatic habitats. The major component of the high-protein diet is fish carrion, which is more abundant in the cooling reservoir than in the other habitats. Both field and laboratory feeding electivity indices show turtles select fish meat over most other food items. Other dietary components include insects, snails, algae, seeds and aquatic vegetation. Elevated water temperatures influence the feeding ecology of turtles by increasing ingestion rates. Previous studies on other digestion processes (assimilation efficiencies, enzyme and gastric acid activity, hormone levels and motility rates) are incorporated into a feeding strategy model for optimizing growth. Elevated water temperatures in the cooling reservoir may also permit an extension of the turtle's growing season.
We provide experimental evidence for the isoleg theory of habitat selection in a pair of psammophilic gerbil species. Gerbillus allenbyi (mean mass: 26 g) and G. pyramidum (mean mass: 40 g) coexist in Israel's Negev desert in areas that may contain three distinct sandy habitats: stabilized sand fields, semistabilized dunes, and drifting dunes. When all three habitat types are available, coexistence between the two species has been explained by a centrifugal model of community organization that has been untested until now. To begin testing it, we conducted a field experiment in six 1 ha enclosures, each containing similar proportions of two of the sandy-habitat types (stabilized sand and semi-stabilized dune). This experiment tested the following hypotheses concerning the coexistence of the two species: (1) both species prefer the same primary habitat type; (2) G. allenbyi and G. pyramidum exhibit intraspecific density-dependent habitat selection; (3) habitat preference of both G. allenbyi and G. pyramidum is affected by the interspecific density of the other species; and (4) in the presence of the two habits of our experiment, the theory predicts that the habitat preferences of the two gerbil species should collapse from a centrifugal to a shared-preference model of habitat selection. We tested these hypotheses during two summers by measuring activity of the two species after introducing predetermined and different densities of gerbils into the enclosures during eight 3-4 wk long temporal replicates. During each temporal replicate, we further manipulated the density of G. allenbyi. Activity and habitat utilization of the rodents was measured by tracks left in the sand. Results of the experiments supported all four of our hypotheses and allowed the construction of their isoleg graph.
We have tested two hypotheses which may explain two different patterns which underlie coexistence in two species of desert gerbils (Gerbillus allenbyi and G. pyramidum). The two patterns are temporal partitioning of foraging activity and shared preference habitat selection. When sympatric, G. pyramidum uses the early part of the night most heavily while G. allenbyi is most active in the late part of the night. Although both species prefer the same habitat type (semistabilized sand dune), in the presence of G. pyramidum, G. allenbyi utilizes mainly the secondary habitat type (stabilized sand dune). The hypotheses are 1) one species is dominant (G. pyramidum) while the other (G. allenbyi) is an energetically more efficient forager, and 2) one species has the ability to quickly harvest seeds in dense resource patches and the other species can harvest seeds profitable at lower resource densities. We tested the hypotheses in an experiment conducted in four enclosed plots. Two additional unfenced plots served as controls. Two of the enclosed plots contained mixed populations of both species while the other two fenced plots contained G. allenbyi only. In contrast to patterns of activity of G. allenbyi with G. pyramidum present, G. allenbyi is also very active early in the night even on the semistabilized dunes when G. pyramidum is absent. The results of the experiment supported the hypothesis that interference is the key factor to understanding the coexistence of the two species. Both the temporal and spatial patterns are the result of the dominant G. pyramidum species excluding the energetically efficient G. allenbyi from the preferred time of activity and habitat type.
In mixed-species flocks, the heavier tit species forage in the inner tree parts, while the smaller species exploit food items of the outer canopy. Using aviary experiments we studied the relative importance of two possible explanations for body size-foraging site correlation. The first hypothesis is that larger bodied tits are more efficient than smaller ones in exploiting the inner tree parts, while the reverse would be true in the outer canopy. However, the heavier species, the Willow Tit Parus montanus, was not more efficient in food searching in the inner tree parts than the smaller species, the Coal Tit Parus ater. The second hypothesis is based on interference competition with the socially dominant (heavier) species selecting the most profitable foraging sites, and forcing the smaller species to less rewarding places. In fact, in confrontation experiments only individuals of the smaller species changed their foraging sites in the presence of an individual of the other species in the aviary. In sum, body size influences social dominance relations and thereby relegates the smaller species to poorer foraging sites, but presumably gives them an advantage in exploitation competition via reduced energy demands for basal metabolism.
Basking, food habits, habitats, and other features of the niches of smooth (Trionyx muticus) and spiny (T. spiniferus) softshell turtles were studied in Iowa from 1969 through 1975. Spiny softshells are more versatile than smooth softshells in basking site selection and toleration of aquatic habitats. Although the same kinds of food are eaten, spiny softshells are primarily benthic feeders and scavengers, whereas smooth softshells feed more in the water column. Niches of the two species differ fundamentally in Iowa yet show considerable overlap.
A study of the community ecology of neotropical freshwater turtles revealed feeding differences between Kinosternon leucostomum, Staurotypus triporcatus, and Trachemys scripta. Quantitative analysis of the flushed stomach contents showed a wide degree of food overlap between the species. The Shanon-Wiener diversity index H′ suggested that Staurotypus was a mollusk specialist under some conditions, but consumed a much higher quantity of plant material (seeds) than previously assumed. Kinosternon leucostomum was an omnivorous generalist in both populations studied. In one lake, in which Staurotypus was absent, the quantity of animal prey consumed by Kinosternon was significantly higher than in the other lake in which Staurotypus also occurred. The population of Kinosternon consuming more animal prey grew faster and larger, and had larger clutches of larger eggs. Sexual dimorphism of head size in Kinosternon was not related to dietary differences in the populations studied.
Comparisons were made between populations of Sternotherus minor and S. odoratus from five localities in northern Florida where they were allopatric, and two localities where they were sympatric. It was determined that the two species compete for food resources where they are sympatric since they overlap considerably in resource utilization, and do not spatially or temporally partition food resources. S. minor loses its specialized mollusk-eating adaptations at localities where it is sympatric with S. odoratus, or at those localities where the snail Goniobasis is absent. It is suggested that character convergence has been demonstrated at localities where the species are sympatric as a result of competition between the turtle species for generalized resources.
1. The spatial distribution of foraging predators differing in foraging traits was investigated theoretically. Three types of individual differences were investigated: dominance that determines the outcomes in fights for food, searching efficiency and prey handling efficiency. The basic assumptions were: (i) predators search for prey; (ii) encountered prey takes time to handle; (iii) the handling process may be interrupted by a searching competitor initiating a conflict about the prey; (iv) conflicts take an expected time to settle; and (v) the winner resumes handling and the loser resumes searching. 2. Stable equilibrium distributions were found in all cases, in the sense that no competitor could achieve a higher intake rate from switching patch. 3. When it was assumed that each of the predators was different from the others, the ideal free distributions of the dominance model and the handling efficiency model resembled one another. A boundary phenotype existed with more dominant/efficient competitors only occurring in the high prey density patch and less dominant/efficient ones occurring mixed across patches. This was labelled semitruncated distribution. In the search efficiency model, the distribution was truncated, i.e. competitors less efficient than the boundary phenotype only occurred in the high prey density patch whereas the more efficient competitors occurred in the low prey density patch. 4. The models were also analysed with the predators classified into two types. As the density of competitors increased, the solution approached a set of neutral equilibria where a few predators of the more efficient type could be exchanged for a larger number of the less efficient type to reach a new equilibrium. 5. The density of predators may be negatively correlated with patch productivity and prey density when predators differ in handling efficiency. Prey-searching efficiency of predators was negatively correlated with predator density, patch productivity and prey density. Its consequences for the conservation of species are discussed.
Three species of map turtle, Graptemys geographica, G. ouachitensis and G. pseudogeographica, inhabit the Mississippi River near Stoddard, Vernon Co., Wisconsin. Adult females of all three species are of similar size and are distinctly larger than males. One species, G. geographica, has a notably wider head than the other two. Quantitative analysis of fresh stomach contents of 113 adult females, qualitative analysis of 74 others and feeding observations confirm that the three species use different foods and feeding strategies. Graptemys geographica is a carnivore specializing on mollusks. Graptemys ouachitensis is an omnivore, but specializes in surface feeding. Graptemys pseudogeographica is a general omnivore overlapping the other two species both in food and feeding areas. Graptemys geographica seems to be limited by food availability. Graptemys ouachitensis represents 66% of the Graptemys in the study area and may be best at exploiting an apparently unlimited food resource of aquatic vegetation and insect larvae. In Arkansas, G. pseudogeographica is a mollusk specialist, possibly due to lack of competition from G. geographica and competition from the ubiquitous generalist, Pseudemys scripta, and the strict vegetarian, Pseudernys concinna.
Two groups of box turtles (Terrapene carolina carolina) were observed for 15 weeks in pens where they competed for daily rations of meal worms. Hierarchies based on competitive-encounters won or lost were reliably stable and were accompanied by behaviours ranging from biting to pushing. Hierarchies based on precedence to initial meal worms within sessions were not reliable as the turtles did not anticipate or respond quickly to the onset of food availablity.
A model is developed to predict potential net energy gain for salmonids in streams from characteristics of water velocity and invertebrate drift. Potential profit was a better predictor of specific growth rate for coho salmon Oncorhynchus kisutch than for brook trout Salvelinus fontinalis or brown trout Salmo trutta. Coho salmon always achieved higher specific growth rates than either brook trout or brown trout in concurrent experiments, and maintained growth to lower resource thresholds. Fish established intraspecific hierarchies and dominant fish held positions affording maximum potential profit. The use of potential profit as an optimal foraging model was tested by predicting the potential for net energy gain at coho salmon positions from the overall pattern of flow and invertebrate drift in the stream aquarium, and ranking these positions from highest to lowest potential profit. This predicted ranking was nearly identical to the rank observed in the linear dominance hierarchy.-from Author
Current models of interference-based ideal free theory often use the coefficient of interference,m, to quantify the intensity of competitive interference. However, it is not clear whatmmeans in terms of behaviour. This is because the Hassell & Varley model, from whichmis derived, only provides a description of the interference process without alluding to the mechanisms underlying the relationship. In this paper a behaviour-based, analytical model is described which finds the ideal free distribution of predators searching for food in a patchy environment. An interference expression from a model developed by Ruxton et al. (1992,Theor. Pop. Biol.,42,235-253) based on the interactions of a group of predators with each other and their prey is used to obtain the ideal free distribution over any finite number of food patches for different prey distributions. Using examples of environments with two and three patches, the effects of the degree of interference and the total prey density on such distributions are also studied. Contrary to many published results, an over-representation of predators in the best patch is always predicted. This effect is enhanced by increasing prey abundance. When interference is the result of wasted time,mcannot exceed 1; in most casesmis expected to be very low.
Biologists are nearly unanimous in their belief that humanity is in the process of extirpating a significant portion of the earth's spe cies. The ways in which we are doing so reflect the magnitude and scale of human enterprise. Everything from highway construction to cattle ranch ing to leaky bait buckets has been implicated in the demise or endan germent of particular species. Ac cording to Wilson (1992), most of these activities fall into four major categories, which he terms "the mind less horsemen of the environmental apocalypse": overexploitation, habi tat destruction, the introduction of non-native (alien) species, and the spread of diseases carried by alien species. To these categories may be added a fifth, pollution, although it can also be considered a form of habitat destruction. Surprisingly, there have been reIa tively few analyses of the extent to which each of these factors-much less the more specific deeds encomDavid S. Wilcove is a senior ecologist at the Environmental Defense Fund, Wash ington, DC 20009. David Rothstein re ceived his J.D. in 1997 from Northeastern
Aggressive interactions, foraging behaviour, microhabitats, and growth of individuals of two sympatric stream-dwelling salmonids, white-spotted charr (Salvelinus leucomaenis) and masu salmon (Oncorhynchus masou masou), were studied in a mountain stream in central Japan. The fishes within a single pool in the stream formed an interspecific size-structured dominance hierarchy. Dominant individuals of both species maintained foraging territories against both subordinate conspecifics and heterospecifics, whereas subordinate charr adopted nonterritorial tactics. In each species, the most dominant fish usually held the focal point nearest to the pool inlet, which ensured priority of access to drifting food, with subordinates distributed farther downstream. Foraging microhabitats differed vertically in the water column between the two species, charr utilizing a home range near the stream bed and salmon occupying the midlayer. The frequency of foraging attempts by salmon was considerably higher than that by charr. Although daily body mass increments of dominant individuals were significantly larger than those of conspecific subordinates in each species, those of some subordinate salmon exceeded those of dominant charr.
A model is developed to predict potential net energy gain for salmonids in streams from characteristics of water velocity and invertebrate drift. Potential net energy gain, or potential profit, is calculated for individuals of three species of juvenile salmonids in a laboratory stream aquarium, based on the energy available from drift minus the cost of swimming to maintain position. The Michaelis–Menten or Monod model is used to describe the relationship between potential profit and specific growth rate. Potential profit was a better predictor of specific growth rate for coho salmon (Oncorhynchus kisutch) than for brook trout (Salvelinus fontinalis) or brown trout (Salmo trutta). Coho salmon always achieved higher specific growth rates than either brook trout or brown trout in concurrent experiments, and maintained growth to lower resource thresholds. In each experiment, fish established intraspecific hierarchies and dominant fish held positions affording maximum potential profit. The use of potential profit as an optimal foraging model was tested by predicting the potential for net energy gain at coho salmon positions from the overall pattern of flow and invertebrate drift in the stream aquarium, and ranking these positions from highest to lowest potential profit. This predicted ranking was nearly identical to the rank observed in the linear dominance hierarchy. The results of experiments confirm ideas of other investigators about mechanisms of microhabitat selection by stream salmonids.
Most of the (infrequent) interactions between adult females were neutral. Non-mating encounters between males and females were evenly divided between non-agonistic and agonistic interactions, and males usually dominated in the latter. Of the encounters observed between males, 88% were agonistic. Of those, 66% involved physical contact. Male-male encounters of all kinds were significantly more frequent in the autumn than in the spring; a significantly higher proportion of autumn encounters were agonistic. The turtles were not territorial. The outcomes of the dominance encounters between males revealed an essentially linear rank order that was positively correlated with age and weight. Mating behavior was observed from April through October, but was concentrated in early spring and especially in autumn. Most mounting sequences lasted from 1-5h, but some lasted for several days and nights. No sperm was found in the cloacas of females immediately after 76.4% of the observed mounting sequences, and only a trace of sperm was found in 8.1%. The other 15.5% of the sequences ended in copulatory ties, and in all of these instances the cloacas of the females were filled with sperm. Because there was a single annual period of egg-laying in June, it was assumed that females store sperm over winter. Some females mates with several males between ovulatory periods, raising the possibility of sperm competition. There was a significant correlation between male rank and various behavioral measures of apparent mating success. Results were confirmed by a paternity study using DNA fingerprinting. -from Author
This book summarizes knowledge about invasive species and the problems that they cause in 7 chapters, with the following titles: a framework for the study of invasions; the origins and success and failure of invasions; which communities are invaded by which type of species; the process of spread; ecological consequences of invasions; genetic and evolutionary effects; and implications and communities. Author and subject indexes are provided.
The threat sensitivity hypothesis assumes that multiple cues from a predator should contribute in an additive way to determine the degree of risk-sensitive behaviour. The ability to use multiple cues in assessing the current level of predation risk should be especially important to prey exposed to multiple predators. Wall lizards, Podarcis muralis, respond to predatory attacks from birds or mammals by hiding inside rock crevices, where they may encounter another predator, the smooth snake, Coronella austriaca. We investigated in the laboratory whether chemical cues may be important to wall lizards for detection of snakes. The greater tongue-flick rate and shorter latency to first tongue-flick in response to predator scents indicated that lizards were able to detect the snakes' chemical cues. We also investigated the use of different predatory cues by lizards when detecting the presence of snakes within refuges. We simulated successive predator attacks and compared the propensity of lizards to enter the refuge and time spent within it for predator-free refuges, refuges containing either only visual or chemical cues of a snake, or a combination of these. The antipredatory response of lizards was greater when they were exposed to both visual and chemical cues than when only one cue was presented, supporting the threat sensitivity hypothesis. This ability may improve the accuracy of assessments of the current level of predation risk inside the refuge. It could be especially important in allowing lizards to cope with threats posed by two types of predators requiring conflicting prey defences.
The effects of inter and intraspecific encounters among the predatory asteroids Crossaster pap- posus (L.) and Asterias rubens L. were monitored in the laboratory by time lapse photography in the presence or absence of a common food item. A. rubens readily aggregated on food whereas C. papposus did not because of strong contact-mediated instraspecific avoidance. The lack of intraspecific avoidance among A. rubens aided its opportunistic exploitation of abundant food. Intraspecific avoidance is suggested as a possible dispersal mechanism of C. papposus. C. papposus interfered with A. rubens in the presence of a common food source and prevented the latter from aggregating due to interspecific avoidance resulting from encounters. This interference mechanism may enhance access to food for C. papposus in the presence of A. rubens.
Animals regularly come into conflict with other members of their own species; this book is about the behaviour used by animals (both human and non-human) to resolve conflicts of interest and how aggression relates to their ecological and social environment. A wide range of important issues are introduced, the scene having first been set by a survey of the variety of aggressive behaviour shown by different animal groups. . . . The book goes on to look at different facets of the biological study of animal conflict, taking in turn motivational studies and the role of environmental stimuli; the hormonal and neurophysiological bases of agonistic behaviour; genetic and environmental influences on its development; the consequences of conflict for the individual, population, community and species; the evolutionary history of fighting behaviour and its adaptive significance. Finally, the relevance of these different kinds of study to our understanding of human aggression is discussed. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Reviews biological invasion theory, with a strong slant towards mathematical analysis (especially using the diffusion equation).
The nature of competitive interactions between native and introduced invasive species is unclear. In the Iberian Peninsula, the introduced red-eared slider (Trachemys scripta elegans) is an invasive species that is competing and displacing the endangered native Spanish terrapin (Mauremys leprosa). We hypothesized that interspecific differences in antipredatory behavior might confer competitive advantages to introduced T. scripta. We examined whether interspecific differences in responses to predation risk affect the time that turtles remained hidden in the shell before using an active escape to water. Both turtle species adjusted hiding times by balancing predation threat, microhabitat conditions and the costs of remaining hidden. However, introduced T. scripta showed longer hiding times before escaping than native M. Leprosa, which, in contrast, switched from waiting hidden in the shell to escape to deep water as soon as possible. These interspecific differences might result from the risk of facing different types of predators in different microhabitats (land vs. water) in their original habitats. However, in anthropogenically altered habitats where predators have been greatly reduced, T. scripta may avoid potential costs of unnecessary repeated escape responses to water (e.g. interruption of basking). These behavioral asymmetries could contribute to the greater competitive ability of introduced T. scripta within anthropogenically disturbed environments.
Groups of four Atlantic salmon parr were established and the dominant individual identified. Feeding responses were then observed in the remaining (subordinate) fish housed in one of three conditions: in the same compartment as the dominant fish (full exposure), separated from it by a transparent partition (visual exposure) or behind an opaque partition (isolated). Subordinate parr in the full exposure condition responded to and ate fewer food pellets than did the dominant fish. However, subordinate parr in the visual exposure condition and in the isolation condition fed actively, indicating that neither visual intimidation nor long-term stress-induced reduction of appetite were responsible for the reduced food intake of subordinate parr in direct contact with dominants. Dominant parr and subordinates in the visual exposure condition, but not subordinates in the exposed condition, moved further from their feeding station when attacking food items that were contested by a competitor compared with the distance moved for uncontested items. The presence of a competitor therefore forced both dominant and visually exposed subordinates to pay higher costs while foraging.
A model of patch choice, in which individuals choose between two sites with different continuous input rates, is presented. Individuals differ in their competitive ability and may not perceive small resource differences between these patches. The model is historical, in that the individuals are added to the system sequentially, building up a complete system. Including this historical aspect leads to a different result from that derived using equilibrium-centred models. Monte Carlo simulations of the model show that (1) the historical development of a distribution of animals significantly affects its final form, and (2) an equilibrium distribution may not be reached until long after all individuals are present. When individuals have different competitive abilities, the ‘free’ assumption of the ideal free distribution (IFD) is violated, giving rise to a distribution we call the ideal competitive-differences distribution (ICDD). As has been previously noted, several different ICDD outcomes are possible in a given situation, but our historical perspective suggests that deviations from the habitat-matching prediction of the IFD (usually undermatchings) are much more likely than previously realized. A widely cited example of the ICDD, for instance, fails to give the IFD-mimicking habitat-matching distribution as its most likely outcome. Lastly, perceptual limits in conjunction with competitive differences result in mismatches with the ICDD. It is suggested, therefore, that experimental results are likely to undermatch resources compared with predictions from both the IFD and the ICDD.