Turtle Hatchlings Research Articles

Etnozoologi Masyarakat Pesisir Seruway Aceh Tamiang Dalam Konservasi Tungtong Laut (Batagur Borneoensis)

ABSTRACT Painted terrapin (Batagur borneoensis) is one of the reptiles found in the coastal area of Pusong Seruway Island, Aceh Tamiang Regency. Currently, the existence of wild population of painted terrapin is threatened to extinction due to factors of nature and community activities. The local government of Aceh Tamiang Regency has already protected painted terrapin (Batagur borneoensis) and listed it as protected species. This research is a descriptive exploratory survey to reveal the symptom and phenomenon of communities concerning their participation in the conservation of painted terrapin (Batagur borneoensis). Result of research was based on survey conducted in three villages with samples of 100 respondents given questionnaire through purposive random sampling technique. Data of ethnic communities consisted of; Tamiang, Aceh, Javanese, Batak and Arabic. Ethnozoology of communities obtained value local knowledge of communities as a form of awareness on animal protection included; participation in the sea turtle hatchling release, reduction in the exploitation activity of utilizing painted terrapin eggs (Batagur borneoensis) as srikaya (food) and traditional medicine, willingness not to take or disturb the animal and if they find painted terrapin (Batagur borneoensis), they will return the animal to its habitat or give it to the conservation team. A small part of the community joined in the assistance rescue group for painted terrapin (Batagur borneoensis). Keywords: ethnozoology, conservation of painted terrapin (Batagur borneoensis).

Using an in-situ infra-red camera system for sea turtle hatchling emergence monitoring

We tested for the first time the efficiency of the use of infra-red (IR) cameras for sea turtle hatchling monitoring. The cameras were installed on one green turtle ( Chelonia mydas ) and four loggerhead turtle ( Caretta caretta ) nests during 2014 and 2015 nesting season in the south-east Mediterranean, Turkey. The camera monitoring, even with the limited sample size, have successfully corroborated the previous observations and provided further insights on hatchling emergence behavior. The analysis of the camera recordings revealed that hatchlings emerged from the nests asynchronously in varying numbers of groups and different group sizes, while c. 60% hatchlings emerged during the first 5 days of emergence activity. 98.6% of hatchlings emerged at night with a peak activity between 21:00 and 00:00. The day of first emergence varied between 38 and 64 days since egg deposition, while the day of last emergence varied only between 60 and 65 days. Total emergence activity continued up to maximum of 22 days, which is longer than that of previous records. Overall, the present study showed that IR camera monitoring is a promising tool for sea turtle monitoring and can provide detailed insights on sea turtle hatchling behavior.

Effects of local climate on loggerhead hatchling production in Brazil: Implications from climate change

Sea turtle eggs are heavily influenced by the environment in which they incubate, including effects on hatching success and hatchling viability (hatchling production). It is crucial to understand how the hatchling production of sea turtles is influenced by local climate and how potential changes in climate may impact future hatchling production. Generalized Additive Models were used to determine the relationship of six climatic variables at different temporal scales on loggerhead turtle (Caretta caretta) hatchling production at seventeen nesting beaches in Bahia, Espirito Santo, and Rio de Janeiro, Brazil. Using extreme and conservative climate change scenarios throughout the 21st century, potential impacts on future hatching success (the number of hatched eggs in a nest) were predicted using the climatic variable(s) that best described hatchling production at each nesting beach. Air temperature and precipitation were found to be the main drivers of hatchling production throughout Brazil. CMIP5 climate projections are for a warming of air temperature at all sites throughout the 21st century, while projections for precipitation vary regionally. The more tropical nesting beaches in Brazil, such as those in Bahia, are projected to experience declines in hatchling production, while the more temperate nesting beaches, such as those in Rio de Janeiro, are projected to experience increases in hatchling production by the end of the 21st century.

Comparación de dos dietas en la adaptabilidad al cautiverio de neonatos de tortuga golfina en Choluteca, Honduras

En Honduras desde el año 1974 se realizan acciones para contribuir a preservar la tortuga golfina Lepidochelys olivacea en el Golfo de Fonseca con la instalación de campamentos tortugueros, pero al hacer liberaciones en la fase de neonato la tasa de sobrevivencia es baja. El objetivo consistió en comparar la adaptabilidad, el crecimiento y la sobrevivencia de neonatos alimentados con una dieta comercial para tilapia y otra con carne de corvina durante 35 días en cautiverio. El estudio se realizó en el laboratorio húmedo del CURLP, se recolectaron 12 neonatos de la playa de Punta Ratón con peso promedio de 17 g, estos se distribuyeron en seis recipientes de 0.22 m3 y mantuvieron con agua marina filtrada, se manejaron como tratamientos la alimentación de carne fresca de corvina y alimento formulado de tilapia al 35% de proteína cruda durante 35 días, se hicieron tres réplicas de cada tratamiento. Se evaluó la adaptabilidad, el crecimiento en peso y en la longitud curvo de carapacho (LLC). Los neonatos demostraron una adaptación al cautiverio y no fueron influenciados por el tipo de alimento suministrado, de igual forma no se encontraron diferencias estadísticas en los crecimientos semanales y finales en peso y en LCC en los neonatos.Se logró al final del experimento el 100% de sobrevivencia en los dos tratamientos.La dieta de tilapia puede utilizarse para alimentar a los neonatos de tortugadebido a su composición nutricional y puede ser una opción por la accesibilidad y costo, así como su uso para el crecimiento de los neonatos en cautiverio.

Towing a Float Decreases Swim Speed but Does Not Affect Swimming Behavior During Offshore Swimming in Sea Turtle Hatchlings

Swimming behavior and speed of green turtle (Chelonia mydas) and hawksbill turtle (Eretmochelys imbricata) hatchlings swimming offshore were compared between individuals that were free swimming and the same individuals towing a float. Towing a float did not influence swimming behavior in either species, but decreased swimming speed by 20% in green turtles and 50% in hawksbill turtles.

High predation of marine turtle hatchlings near a coastal jetty

Growing human populations are driving the development of coastal infrastructure such as port facilities. Here, we used passive acoustic telemetry to examine the effects of a jetty and artificial light on the rates of predation of flatback turtle (Natator depressus) hatchlings as they disperse through nearshore waters. When released near a jetty, around 70% of the tagged hatchlings were predated before they could transit the nearshore, irrespective of the presence or absence of artificial light. Only 3 to 23% of hatchlings encountered predators at a second study site nearby where there was no jetty and a similar amount of nesting activity. Evidence for predation was provided by rapid tag detachment due to prey handling by a predator or the extensive movement of the tags within the receiver array suggesting that the tag (and hatchling) was inside the stomach of a predator. We found that 70% of the fish predators that consumed tags used the jetty as a refuge during the day and expanded their range along nearshore waters at night, predating on hatchlings in areas adjacent to the jetty with the highest nesting density. Sampling of potential predators including lutjanid reef fishes under the jetty revealed the presence of turtle hatchlings in their gut contents. By providing daytime refuges for predators, nearshore structures such as jetties have the potential to concentrate predators and they may pose a significant threat to populations of vulnerable species. Such effects must be taken into consideration when assessing the environmental impacts associated with these structures.

Do Sea Turtles Vocalize to Synchronize Hatching or Nest Emergence?

Sea turtle hatchlings are known to vocalize; however, the purpose of these vocalizations is currently unknown. One hypothesis is that these vocalizations serve to synchronize hatching or starting the emergence from the nest. To test this hypothesis, we characterized and compared the frequency and duration of the sounds made by Olive Ridley Turtles (Lepidochelys olivacea) during incubation, hatching, and emerging from the nest. We also determined whether hatchlings continue to vocalize after emerging from the nest. Lastly, we investigated species-specific variations in the vocalizations of Olive Ridley, Leatherback (Dermochelys coriacea), and Green (Chelonia mydas) turtle hatchlings. Sound production was more frequent during incubation than during hatching or emerging from the nest, and in two of the three nests, a unique ‘pulse’ sound was heard during incubation. However, there were no significant differences in the frequency range or duration of the vocalizations between incubation, hatching, and emerging from the nest. Furthermore, hatchlings were recorded and continued to vocalize after emerging from the nest. From this we conclude it is unlikely that the sounds made by the hatchlings help to synchronize hatching or emergence behavior. Instead, they are likely by-products of other processes, such as embryo movement, serving little biological purpose. Nevertheless, we recommend further research to unequivocally confirm this is the case, and it remains highly interesting that sound production is a universal trait among cheloniid species.

Sex Determination in Green Turtle Hatchlings: Geometric Morphometry and Molecular Sex Markers

Determination of the sex ratio in sea turtle population is one of the most important parameters for
 the conservation and management of the species. We aimed to the test usability of the more than
 one approaches that identify the sex of hatchlings with alternative non-invasive methods.
 Geometric morphometry and molecular sex marker were used to indicate difference between the
 sexes in the green sea turtle (Chelonia mydas) hatchlings which sexes were previously determined
 by gonad histology. A total of 60 landmarks were identified from three body parts (carapace,
 plastron and tail) for geometric morphometry. No sex specific difference was found in these three
 body parts. Furthermore, we analyzed a total of 55 different oligonucleotide combinations using
 sex-based pool strategy but found no difference. These two techniques are insufficient for sex
 determination in the green turtle hatchlings. A relatively small number of the primer combinations
 and male hatchlings used to identify sex of C. mydas appears to be a disadvantage. In order to
 obtain clearer results with geometric morphometric and molecular sex markers, it is recommended
 to compare sexes in laboratory conditions with constant temperature.

Effects of sand type on hatch, emergence, and locomotor performance in loggerhead turtle hatchlings

While numerous problems have been identified regarding artificial management of sea turtle eggs, the development of methods and techniques for rearing the eggs, such as relocation and incubation in hatcheries, should be considered an effective approach for the conservation of sea turtles. As sand size is hypothesized to affect the timing of the nest-atrium collapse and hatchling fatigue, one of the important aspects of incubation environment in the hatchery is likely sand. We examined the influence of nest-sand type on hatching characteristics and hatchling quality in loggerhead turtles (Caretta caretta). We collected the eggs from nine nests in the wild and incubated them in two kinds of sand groups in a hatchery. One group of eggs was incubated in fine sand and the other was incubated in coarse sand. Compared to the nests comprising coarse sand, hatchlings from fine-grain sand nests had significantly higher crawling and swimming performance. To increase hatchling survival and performance, fine-grain sand is recommended for use in incubation beds in artificial hatcheries.

Marine debris as a barrier: Assessing the impacts on sea turtle hatchlings on their way to the ocean

Marine debris is dispersed worldwide and has a considerable impact on biodiversity. In this study, the effect of marine debris on the time needed for hatchling loggerheads to reach the ocean once they have emerged from the nest was investigated. After a preliminary census of marine debris on different beaches of Boa Vista Island, Cape Verde, a field test was carried out with four different scenarios: low density marine debris, medium density marine debris, high density marine debris, and a control scenario. The time that hatchlings required to cross the different scenarios was recorded (n = 232). The results showed that crawl times were affected by the different marine debris scenarios, with the “high density” scenario specifically showing a significant difference from the control, low density and medium density scenarios. This study provides information on the risks of marine debris for hatchling sea turtles and provides conservation recommendations to reduce this potential risk.

Colour vision of green turtle (Chelonia mydas) hatchlings: do they still prefer blue under water?

BackgroundSeveral anatomical studies provide evidence that green turtles (Chelonia mydas) possess the necessary anatomy for colour vision. Behavioural experiments have previously been conducted with newly emerged hatchlings, concluding that they are attracted to shorter wavelengths compared to longer wavelengths within a terrestrial environment, suggesting a possible attraction towards blue. This paper assessed the colour vision of hatchlings within an aquatic environment, and investigated whether the attraction for shorter wavelengths remains consistent within water, whether the colour saturation of the chromatic stimuli was an important factor, and whether rearing and testing individual animals in different coloured housing tanks has an impact on their visual choices.MethodsForty-one hatchling green turtles were presented with a three-choice experiment where food was attached to three different coloured plates. The plates (blue, yellow, and red) were randomly arranged in the turtle’s tank and four different colour saturations were tested (100, 75, 50, and 25%). Turtles were individually placed into their housing tanks (coloured either red, white, blue or grey) with three different colour plates in front of them, from the same saturation level. The colour of the plate with food first approached and bitten by the turtle was recorded.ResultsThe colour of the tank in which an individual was reared, and where experiments were conducted, significantly influenced which food item was selected on the different coloured plates. While individual turtles preferred to select the food items associated with blue plates across the entire experiment (66.1% of the time compared to 18.2% and 15.7% for yellow and red plates respectively), the preference for blue plates was influenced by the colour of the rearing/experimental tank. Individuals raised in red, white or blue tanks appeared to consistently prefer food on blue plates, but there appeared to be no plate colour preference by turtles in grey tanks. There was no significant effect of either colour saturation or the spatial arrangement of the three colours within an experimental tank on colour choice, and no significant interaction between tank colour and colour saturation.DiscussionThesefindings confirm that the terrestrial preference towards shorter wavelength colours, such as blue, compared to longer wavelength colours remains consistent within an aquatic environment. This preference for blue continues even as the colour saturation reduces from 100% down to 25%, and the colours become darker. Thus, it is suggested that green turtle hatchlings have a strong attraction towards blue. This attraction, however, is influenced by the colour of the tank the turtles were raised in. While this supports the notion that environmental colour may influence individual turtle visual capabilities, it suggests that this relationship is more complicated, and requires further investigation.

Incubation and water temperatures influence the performances of loggerhead sea turtle hatchlings during the dispersal phase

Artificial manipulation of incubation temperature has been proposed as a potential strategy for mitigating the effects of climate change on sea turtles for which sex determination is temperature-dependent, but thermal manipulation may also affect hatchling survival. Here, we demonstrated that incubation and water temperatures influenced several performance traits that contribute to the survival of loggerhead sea turtles (Caretta caretta) during the post-hatchling dispersal phase. Hatchlings from warm incubation temperatures (31 °C) had significantly shorter incubation periods, higher initial swimming performance, lower sustained swimming performance, and lower growth rates during the first three weeks post-hatching, as well as higher blood glucose concentrations, than those from cool incubation temperatures (27.5 °C). Hatchlings in warm water temperatures (30 °C) exhibited significantly greater swimming performance than those in cool water temperatures (27 °C). Our results indicated that altering incubation temperatures indirectly influences the survival of loggerhead hatchlings by modifying their swimming performance and growth rates, which may affect hatchling predator-avoidance capability. Moreover, thermal manipulation may alter the incubation period, exposing hatchling to water temperatures that they would not otherwise normally experience, which may affect swimming performance. Our results suggest that such conservation strategies may influence their survival, and thus should be carefully considered.

Water exchange relationships predict overwintering behavior in hatchling turtles

Neonatal ectotherms face a wide range of environmental hazards because of the diverse habitats that they inhabit and their small body sizes; this is especially true among turtles that live in temperate zones and experience cold winter conditions after hatching. Such hatchlings must balance challenges involving desiccation, freezing, and predation, among other threats. Turtle hatchlings either overwinter in water, terrestrially in relatively shallow nests, terrestrially deep below nests, or terrestrially outside of the nest entirely, and these different microhabitats are associated with different desiccation and freezing risks. We measured desiccation tolerance of individuals of six turtle species, including two (Diamondback Terrapins, Malaclemys terrapin (Schoepff, 1793), and Eastern Box Turtles, Terrapene carolina (Linnaeus, 1758)) that use a strategy that has not previously been explored, along with Wood Turtles (Glyptemys insculpta (Le Conte, 1830)), whose overwintering microhabitat is uncertain. We found additional support for the hypothesis that desiccation resistance is associated with overwintering strategies in hatchling turtles. Further investigation into the overwintering strategies of M. terrapin and T. carolina would be productive.

Influences of the Local Climate on Loggerhead Hatchling Production in North Florida: Implications From Climate Change

The environment and climate in which sea turtle eggs incubate affects how successful and viable hatchlings are. Therefore, it is crucial to understand how local climate impacts sea turtle hatchling production as well as how potential changes in climate may impact future hatchling production. In this study, we investigated the effects of five different climate variables at different temporal scales on loggerhead sea turtle (Caretta caretta) hatchling production from North Florida, USA. Humidity, air temperature, and accumulated precipitation were the main climatic drivers of hatchling production, while sea surface temperature and wind speed did not demonstrate to have strong effects. Climate projections show air temperatures increasing at the nesting beaches throughout the 21st century, while precipitation and humidity projections vary between sites and projection scenarios. Due to the temperate nature of these nesting beaches, increases in hatching success for nests that incubate undisturbed (not affected by depredation and storm-related impacts) are projected for this region by 2100. This study demonstrates how different climate variables and their interactions can have a determining effect on an important marine species.

Relationship between Metabolic Heating and Nest Parameters in Green Turtles (Chelonia mydas, L. 1758) on Samandağ Beach, Turkey.

Acquiring information about metabolic heating is necessary for the improved understanding of nesting beaches. However, there are limited studies on metabolic heating of green turtle (Chelonia mydas, L. 1758) on Mediterranean beaches. The present study sought to determine the metabolic heating, and its effect on the feminization of green turtle hatchlings during 2016 and 2017 nesting season on Samandağ Beach, Hatay, Turkey. Moreover, the relations between metabolic heating and nest parameters, and spatio-temporal differences of metabolic heating were evaluated. Nest temperatures were recorded by using data loggers placed at the center of nests (n = 18), and the same depth was used to determine the sand temperature that was 50 cm back of the egg chamber. The mean incubation duration was calculated as 51.1 days, and the mean distance of nests from sea and the mean nest depth were measured as 32.4 meters and 67.70 cm, respectively. The mean numbers of embryo that is early, middle and late embryonic stages were found as 110.8, 93.2 and 93.05, respectively. The mean clutch size was found as 110.8. Mean metabolic heating was 0.37°C in the middle third of incubation for both years. The metabolic heating in both years was close to the as reported in the other green turtles nesting beaches in the Mediterranean. The feminization effect of metabolic heating was calculated as 6.8% in the green turtle nests on Samandağ Beach. Metabolic heating did not vary spatially, and the clutch size was the most important factor in metabolic heating and explained a large proportion of the variation in metabolic heating.

Effect of light intensity and wavelength on the in-water orientation of olive ridley turtle hatchlings

Light pollution, associated with coastal development, poses a growing threat to sea turtles. Hatchlings are particularly affected during their crawl to the ocean since they exhibit phototaxis and may move towards or be disoriented by artificial lights. Although much is known about how hatchlings respond to artificial light while crawling to the ocean, far less is known about their response after reaching the water. Here, we investigate how hatchling olive ridley turtles (Lepidochelys olivacea) held in artificial pools responded to light of different wavelengths (red, 720 nm; yellow, 660 nm and green, 520 nm) and intensities (0.1–3.3 lx, mean 0.87 lx, SD = 0.85, 10.3–45.9 lx, mean 15.75 lx,SD = 7.12; 47.5–84.2 lx; mean 52.02 lx, SD = 9.11; 91.3–140.8 lx, mean 105 lx, SD = 13.24; 150.1–623 lx, mean 172.18 lx, SD = 73.42). When no light or red light below 39 lx was present, hatchlings oriented at a mean angle of 180° from true north and did not orient towards any discernable feature. However, hatchlings swam towards the light at intensities of red light above 39 lx, yellow light above 10 lx and green light above 5 lx. Our findings indicate that sea turtles will swim towards artificial lights even after reaching the water. Thus, we recommend light mitigation efforts should extend beyond nesting beaches and into the associated oceanic habitats.

Depth of the drying front and temperature affect emergence of leatherback turtle hatchlings from the nest

Sea turtles bury their eggs in nests at depths ranging from 25 to 100 cm. After hatching, turtles crawl up to the surface and emerge over several days. Some hatchlings fail to emerge and die in the sand column. In this study, we investigated the effect of the depth of the drying front (the region separating saturated and partially dry sand), number of hatchlings emerging, depth of nest and temperature on the emergence of hatchling leatherback turtles (Dermochelys coriacea) over the course of three nesting seasons (2008–2009, 2011–2012 and 2012–2013) at Playa Grande, Costa Rica. The depth of the drying front affected the number of hatchlings that failed to emerge in all years and high temperature reduced emergence rate in 2008–2009 and 2012–2013, but not in 2011–2012. Most of the variability in emergence rate was explained by the number of hatchlings emerging and the depth of the drying front. The number of dead hatchlings was mainly explained by the depth of the drying front and temperature. Depth zones within the sand column that included the drying front and the egg chamber registered the greatest number of dead hatchlings. The depth of the drying front, temperature and number of hatchlings remaining in the sand column increased and the emergence rate decreased as the season progressed. Leatherback turtles are critically endangered in the eastern Pacific Ocean. Conservation strategies towards improving the conditions in the nest environment (i.e. nest irrigation and shading to decrease the depth of the drying front and temperature) could boost hatchling production and contribute to revert declining population trends.

Reduction of sea turtle population recruitment caused by nightlight: Evidence from the Mediterranean region

The spread of artificial night lighting is increasingly acknowledged as a major threat to global biodiversity. Identifying and exploring the impacts of nightlight pollution upon species behavior, ecology and population dynamics could enhance conservation capacity. Sea turtle hatchlings emerge from nest at night and use visual cues to direct towards the brightest and lowest horizon, eventually leading them to the sea. Nightlight pollution could alter the cues perceived, disorienting the fragile hatchlings. We examined the level of artificial lighting and orientation patterns of sea turtles hatchling, in Zakynthos Island, Greece, one of the main nesting rookeries of the loggerheads (Caretta caretta) in the Mediterranean Sea. We analyzed movement patterns of 5967 hatchlings from 230 nests, and demonstrate that nightlight pollution could reduce population recruitment by more than 7%, suggesting that mitigation measures should become a high conservation priority. Our results further suggest that the responses of sea turtle hatchlings to artificial nighttime lighting could vary significantly depending on various factors, either anthropogenic or natural. Local conditions operating at the nesting site level determine the fine scale responses of hatchlings, thus conservation measures should be drawn in respect to site-specific properties.

Sand type influences the energetics of nest escape in Brisbane river turtle hatchlings

Freshwater turtles can construct their nest in a wide range of soil types, and because different soil types have different physical characteristics such as particle size distribution and compactness, soil type presumably affects digging performance and the energetics of nest escape of turtle hatchlings. Previous studies have reported how cohort size affects the energetic cost of nest escape in turtle hatchlings, but no studies have reported the influence of substrate type on the energetic cost of nest escape. The time taken and the energy required by the same number of hatchlings to dig through two different sand types were quantified by open-flow respirometry. Brisbane river turtle hatchlings digging through fine sand escaped faster and spent less energy than hatchlings digging through coarse sand, and a larger cohort size provided a clear energetic advantage while digging in both sand types. Across all group sizes, hatchlings digging through fine sand spent 33.8% less energy compared with hatchlings digging through coarse sand. We conclude that hatchlings emerging from nests constructed in fine sand have an energetic advantage over hatchlings emerging from nests constructed in course sand because they would have greater energy reserves upon reaching the nest’s surface.

A Preliminary Study of Using Some Nest Characteristics as Indicators for the Size of Green Turtle (Chelonia mydas) Hatchlings

Vucut buyuklugu, deniz kaplumbagasi yavrularinin hayatta kalma sansini artirabilir veya azaltabilir. Deniz kaplumbagasi yavrusunun hayatta kalabilirligi icin vucut buyuklugunun onemi goz onune alindiginda, indikator kullanilarak, yavru buyuklugunun tahmin edilmesi koruma uzmanlari icin yararli bir yontem olacaktir. Turkiye'de Chelonia mydas populasyonunda, yavru buyuklugu icin indikator olup olmayacaklarini belirlemek amaciyla, yumurta sayisi, yuvanin denize olan uzakligi, kulucka suresi ve yuva derinligi gibi bazi yuva ozellikleri yavru buyuklugu ile korelasyona tabi tutuldu. Bulgularimiz, bu yuva ozelliklerinden hicbirinin yavru buyuklugunu tahmin etmek icin uygun olmadigini gostermistir. Ancak, kulucka suresi, yavrunun duz karapas boyu ile zayif bir korelasyon gostermistir. Kollinear yuva ozelliklerinden turetilen ana bilesenlerin (AB), yavru buyuklugune en iyi uyan dogrusal modeli olusturuldugu zaman, model yavru buyuklugundeki varyansin sadece % 19.75'ini acikladi. AB2'nin dogru karapas boyu (DKB) uzerinde anlamli bir etkisi vardi ve AB1 ile AB2 arasindaki etkilesim, tek degiskenli analizde DKB ve egri karapas boyu (EKB) uzerinde belirgin etkilere sahipti. F-test sonuclari, modellerin belirgin ongoru yeteneginin olmadigini onermektedir. Belki de, arastirilmayan diger faktorler indikator olarak daha uygun olabilir veya yavru buyuklugu, indikator olarak kullanilabilir ancak tespiti yapilamayan bir kac temel faktor gibi cesitli faktorler arasindaki karmasik bir etkilesimden etkileniyordur.