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Peterson, Anna C.
Comportamiento de fidelidad de parches en liblulas coexistentes: Hetaerina cruentata (Odonata: Calopterygidae) y Argia extranea (Odonata: Coenagrionidae)
Patch fidelity behavior in coexisting damselflies: Hetaerina cruentata (Odonata: Calopterygidae) and Argia extranea (Odonata: Coenagrionidae)
Patch fidelity in coexisting territorial damselfly species, Hetaerina cruentata and Argia extranea was studied to determine if these species displayed differing territorial behavior, which may be one mechanism for niche differentiation of these species. Data such as light amount and proximity to water of the patch sites were gathered to provide information about territorial preferences of these two species. No significant relationships between patch fidelity and patch characteristics were found. A significant difference was seen between the patch fidelity of the two species, implicating territory as a possible niche differentiating mechanism. Possible explanations for the variation in patch fidelity behavior between the species include: genetic differences between the two species, differences in learning abilities in relation to life span, and differing impacts of population dynamics on H. cruentata and A. extranea.
Fidelidad a pequeos parches entre dos especies de liblulas de la familia Odonata, Hetaerina cruentata y Argia extranea, fue investigado para determinar si hay una diferencia en la conducta territorial de las especies.
Text in English.
Damselflies--Costa Rica--Puntarenas--San Luis
Liblulas--Costa Rica--Puntarenas--San Luis
Tropical Ecology 2006
Ecologa Tropical 2006
Fidelidad de parches
t Monteverde Institute : Tropical Ecology
Patch fidelity behavior in coexisting damselflies: Hetaerina cruentata (Odonata: Calopterygidae) and Argia extranea (Odonata: Coenagrionidae) Anna C. Peterson Department of Ecology and Evolutionary Bi ology, University of Colorado at Boulder Abstract Patch fidelity in coexisting territorial damselfly species, Hetaerina cruentata and Argia extranea was studied to determine if these species displayed differing territorial behavior, which may be one mechanism for niche differentiation of these species. Data such as light amount and proximity to water of the patch sites were gathered to provide information about territo rial preferences of these two species. No significant relationships between patch fidelity and patch character istics were found. A significant difference was seen between the patch fidelity of the two species, impli cating territory as a possible niche differentiating mechanism. Possible explanations for the variation in patch fidelity behavior between the species include: genetic differences between the two species, differences in learning ab ilities in relation to life span, and differing impacts of population dynamics on H. cruentata and A. extranea Resumen Fidelidad a pequeos parches entre dos especies de la familia Odonata, Hetaerina cruentata y Argia extranea, fue investigado para determinar si hay una differencia en la conducta territorial de las especies. Esta conducta es un mecanismo posible de diferenciaci n de estas especies. Datos como la cantidad de luz y la proximidad al ro de las pequenos parchos, fueron colectados para determinar los preferencias territoriales de las especies. No hubo relaciones significativas entre la fidelidad a los parches y las caractersticas de los parches. Hubo una diferencia signi ficativa entre la fidelidad a los parches entre las dos especies, implicando las diferencia s territorales como un mecanismo de posible diferencia. Explicaciones posibles para la diferencia en la conducta de los especies incluyen las diferencias genticas, las diferencias en la habilidad a aprender conductas, y los impactos diferentes de dinmica de poblacional en H. cruentata y A. extranea. Introduction Territories of the family Odonata are defined as any defended area. (Nobel 1939). Males aggressively defend areas near ovipositio n sites where females arrive searching for copulation (Cordoba-Aguilar 1994). Territories are maintained because they are beneficial to the fitness of Odonata species. When returning to a familiar site, a species will already be aware of potential dangers such as spider webs or other dangers. Territories also allow individuals to spend less time looking for potential oviposition sites and instead spend time on more productive activ ities such as hunting or mating (Grether and Switzer 2000). A defended area will sometimes contain individuals of multiple 1
species (Huffaker and Gutierrez 1999). Adults of the Odanata subfamily Zygopter a are predacious, feeding on small flying insects found in riparian areas (Romoser and Stoffolano 1998). Like all insects, they are ectothermic, with most of their heat provi ded by solar radiation and metabolic heat (Romoser and Stoffolano 1998). The two sp ecies studied in this experiment, Hetaerina cruentata and Argia extranea are both predacious, ectothermic and also both display territorial behavior. A. extranea and H. cruentata are found living in coexis tence along the Rio Alndra in San Luis, Costa Rica. Due to their sh ared habitat, similar prey choice and physiological needs, it appears that H. cruentata and A. extranea exhibit a potential for niche overlap. The Lotka-Voltera Principle of Competitive Exclusion states that no two coexisting species can occupy the same ni che at the same time (Begon et. al. 1990). What, then, is the mechanism that differentiates the niches of these species? Studies have shown that local behavioral interactions between individuals can be important mechanisms for explaining coexistence (Mik ami et. al. 2004). Therefore territoriality may be a possible mechanism for differentiating the niches of H. cruentata and A. extranea Territoriality is known to be an important process in the distribution of individuals over a habitat (Bothe and Vi sser 2003). Differences in th e territorial behavior may differentiate H. cruentata and A. extranea in space. For example one species may keep loose territories while anothe r keeps more consistently vi sited or defined territories. Studies have already shown that H. cruentata moves infrequently from its territorial sites, even after multiple days (Cordoba-Aguila r 1994). My study aimed to explore the territorial behavior of H. cruentata further and compare its behavior to that of A. extranea in order to determine if these species display differences in their patch fidelity. This study also considered if patches with high numb ers of faithful individuals had particular characteristics, which would provide informa tion on territorial pref erences of damselfly species in general. It was hypothesized that there would be a difference between the patch fidelity of the two species. It was predicted that the larg est individuals would re turn to patches most often because they would be best able to defe nd their chosen habitat. It was also predicted that the larger H. cruentata would show more patch fidelity because its larger size would make it a better inter-specific competitor. Materials and Methods Study Site This study was conducted along a 1 km stretch of the Rio Alndra about 2 km south east of the Ecolodge in San Luis for a 3 week period during October and November between the hours of 8 a.m. and 2 p.m. This area is typified by open fields visited by few cattle, and grades into more closed secondary fo rest moving upstream. The fifteen study sites used varied in their substrate and included patches of bare rock, open pasture grass and leafy vines, lianas a nd other vegetation. 2
Study subject Two species within th e subfamily Zygoptera: Hetaerina cruentata (Calopterygidae) and Argia extranea (Coenagronidae) were studied in this experiment. H. cruentata is the larger of the species, averaging 4.70 cm in lengt h. It is dark black to brown in coloration. Males of this species have bright red spots on the base of their wings, giving them their common name ruby spot. Females of the species H. cruentata are often more brown in color than males, and lack the red spot on their wings. A. extranea is smaller (averaging 3.65 cm in length) and displays strong sexual di morphism in color; males are bright blue with black rings and females are tan with black rings. Both species are common and fairly widespread in Costa Rica, and usually found below 600 m (Haber personal communication). These species are considered beneficial to humans because larvae of Odonata are aquatic and ofte n feed on mosquito larvae (Romoser and Stoffolano 1998). Methodology I chose fifteen 2 m 2 patches for use in this study. I designated this size for each patch after observing the behavior of H. cruentata and A. extranea This size was also the patch size used by Cordoba-Aguila r (1994) in his study of H. cruentata A patch represents the area of potentially defended territory. These pa tches were marked off at various intervals along the riverbank with flagging tape. I captured all members of H. cruentata and A. extranea within each patch and marked each in dividual with a unique pattern of dots using paint pens and acrylic pa ints, and then measured their size. I observed patches over the course of 3 weeks and made records of any individual found retu rning to a patch. For each patch I measured the size, distance from water, distance from other patches, slope of patch estimated in degrees, substrate, and amount of sun. I used an Extech EasyView Light Meter to take the light data, which I measured over two different clear days between the hours of 11 a.m. and 1 p.m. I collect ed data on patch characteristics such as in order to determine if persistently visited patches had particular characteristics, thus providing more information on territorial preferences of damselfly species in general. I spent five minutes at each perch recordi ng the aggressive behavior. I defined an aggressive behavior as any be havior in which two male dams elflies engaged in chasing or physical contact. If I observed th is behavior between a male and female I did not count it, as it may have been a mating behavior. I reco rded numbers of aggr essive behaviors in order to determine if persistently visited pa tches also had higher levels of aggression. Results In total 71 individuals were captured, 36 individuals of H. cruentata and 35 individuals of A. extranea Individuals of H. cruentata were recaptured in thei r original patch after at least one or more subsequent days with a rate of 80.6% (2 = 7.557, DF = 1, P < 0.01, Figure 1). Individuals of A. extranea were recaptured in their or iginal patch with a rate of 17.1% ( 2 = 7.557, DF = 1, P < 0.01, Figure 1). Ther e was no significant relationship 3
between patch angle and recapture (R2 = 0.251, P = 0.056, n = 28), between patch distance from water and recapture (R2 = 0.183, P = 0.1119, n = 28), or between light amount and recapture (R2 = 0.1138, P = 0.2188, n = 28, Figure 2). A correlation between aggressive behavior and patch fidelity also was found to be non-significant (P = 1.000). There was no significant difference between sizes of H. cruentata individuals recaptured in their original patch and individu als not recaptured (T=-0.074364 DF = 12, P=0.941946, n = 36, Figure 3) or size of A. extranea individuals recaptured in comparison to those not recaptured (T = 0.211604, DF = 5, P = 0.840771, n = 35, Figure 4). 0 5 10 15 20 25 30 35 Hetaerina cruentata Argia extranea SpeciesNumber Recaptured FIGURE 1. Recaptures in original patch of H. cruentata and A. extranea Recaptures between two damselfly species Hetaerina cruentata and Argia extranea differ significantly from each other. H. cruentata was found to return to a patch significantly more often than A. extranea (Chi-Square, 2 = 7.557, DF = 1, P < 0.01). 4
0 1 2 3 4 5 6 7 8 9 020406080100120 Sun Amount (Klux)Total Recaptures FIGURE 2. Total recaptures in relation so sun amount. No relationship between recaptures and amount of sun, measured in Kl ux. Klux data measured with a light meter. Slight trend shows higher le vels of recaptures with greater amount of sun. Linear regression showed no significant relationship (R2 = 0.1138, P = 0.2188, n = 28). Std. Dev. Std. Err. Meansize (cm) 4,54 4,60 4,66 4,72 4,78 4,84 4,90 No recapture Yes recapture FIGURE 3. H. cruentata size by recapture. No significant difference between sizes of H. cruentata individuals recaptured in original patch and size of individuals not recaptured. (T-test for dependent samp les, T=-0.074364 DF = 12, P=0.941946, n = 36). 5
Std. Dev. Std. Err. Meansize (cm) 3,4 3,5 3,6 3,7 3,8 3,9 No recapture Yes recapture FIGURE 4. A. extranea size by recapture. No significant difference between sizes of A. extranea individuals recaptured in original patch and size of individual not recaptured (T-test for dependent samples T = 0.211604, DF = 5, P = 0.840771, n = 35). Discussion Individuals of H. cruentata returned to the same patch of habitat more often than individuals of A. extranea (X2 = 7.557, DF = 1, P<1). Th is supports the original hypothesis that there would be a difference betw een the patch fidelity of the two species. The difference in the territorial behavior of the two species is a plausible mechanism for differentiating the distributions of H. cruentata and A. extranea Territoriality may be the agent responsible for spatially distributing these species, leading to differentiation in other areas of their nich e (Both and Visser 2003). A possible explanation for the lack of relationship between sun amount (R2 = 0.1138, P = 0.2188, n = 28), angle (R2 = 0.251, P = 0.056, n = 28), distance from water (R2 = 0.183, P = 0.1119, n = 28) and patch fidelity is that there may be factors more important to H. cruentata and A. extranea in determining territorial si tes. Gibbons and Pain (1992) found that female Caloptyryx damselflies prefer to ovipos it in patches of aquatic vegetation found in fast water. This study suggests that fast er water may increase oxygen to the eggs, or may reduce parasitism on the eggs. A possible future study could determine if H. cruentata and A. extranea also display this behavior, and prefer sites better equipped to ensure the survival of their offspring. Adult males of the species H. cruentata have been shown to m ove infrequently once a territory is established (Cordoba-Aguila r 1994). In his study Cordoba-Aguilar (1994) recaught 64.8% of the H. cruentata originally captured in his st udy. The return rate in this study was even higher, with 80.6% of H. cruentata individuals recaptured in the same patch, therefore supporting Cordoba-Aguilars findings. Furthermore this study shows that not only do H. cruentata move infrequently from patch areas, but they return to a patch significantly more often than members of the species A. extranea. Only 17.1% of A. extranea individuals were recaptured in the same patch on subsequent days. No significant correlation between the size of indi viduals and their tendency to return to a 6
particular patch area was found; suggesting that the relationship isnt as simple as the bigger damselfly wins the territory most ofte n. What then, could explain the difference between the patch fidelity of H. cruentata and A. extranea ? Females entering a territory are recognized as females through the use of sight (Romoster and Stoffolano 1998). Occasionally males will not recognize the sex of an individual, and will attempt to enter the ta ndem position that precedes copulation with a male rather than female (Johnson 1963). Male s may attempt to avoid this behavior by spreading out into territories. It has been s uggested that sexual encounters between males preceded the evolution of territorial behavi or (Romoser and Stoffolano 1998). It is possible that this same behavior is pres ent in the species ob served in this study. A. extranea displays a high level of sexual dimorphism. H. cruentata displays less obvious sexual dimorphism with so it is possible that H. cruentata has a harder time recognizing females of its species, and consequently has e volved a stronger sense of territoriality in order to avoid negative ma le-male mating behavior. Studies have shown that a high percentage of adults die s hortly after reaching maturity (Johnson 1962). Thus it is thought th at species-species behaviors, such as territoriality, are genetically controlled b ecause members of Odonata simply dont spend enough time as adults to learn this beha vior (Johnson 1962). Cordoba-Aguilar (1994) found that the survival rate of H. cruentata might be as high as 44.9 days, which is the highest rate within the suborder, and perh aps for all odonates in general. This longer lifetime may provide H. cruentata the opportunity to learn territorial behaviors that A. extranea is unable to. H. cruentata may then possess not only genetically embedded knowledge, but also may possess some learned knowledge as well, which may allow this species to have more develope d territorial behavior than A. extranea A final possibility for the difference in perch fidelity between A. extranea and H. cruentata may have nothing to do with learned or genetic behavior s, but rather could be a function of population dynamics. At low densitie s, populations are bette r able to establish territories. At higher densities the costs of defending territories increases, so territories can shrink or behaviors can change (Both and Visser 2003). It is possible that the A. extranea and H. cruentata populations differed at the time of this study; or that these species differ in their response to changing population densities. No population data were collected for either species so it is unknown if the populati ons of the species differed. A possible study for the future could take into account population data for these two species to determine if they do respond differently to changes in population density. It would also be interesting to look closer at other possible differentia ting mechanisms, such as food choice or reproduction, to determine to what ex tent these two species are differentiated in other areas. A. extranea and H. cruentata are species known to defend territories. This study has shown that these species differ significantly in their territorial behavior, suggesting differences in these species utilization of space. The cause of this difference is not known. It may be a genetically programmed response, with each species evolving different territorial behaviors based on male-male copulation avoidance, or that H. cruentata with its longer life span is able to learn territorial be havior and gain and advantage over A. extranea. The difference in behavior of these two species may also be a reflection of the population dynamics presen t at the time of the study. Whatever the reason, it is important to incr ease knowledge of species inte ractions because interactions 7
8 are important to how species utilize space (Both and Visser 2003). This knowledge becomes increasingly important as human be ings change and destroy this space at incredible rates. Acknowledgments First off Id like to thank Bill Haber for his help in identifying my damselfly species and Tania for her advising and making the trip all the way to San Luis Cam, that cake that one nightawesome. In general Id like to thank the worlds best TAs for all their help in editing, preparing snacks, and Tom for getting us lost. Karen and Alan, thanks for a good time. And mostly Id like to thank all my fellow students for your help and humor, and for making even the tough days fun. Except for Lili. Thanks for nothing. Works Cited Begon, M. et. al. 1990. Ecology: Individuals, Populations and Communities. Blackwell Scientific Publications, Boston. Borrar, D.J. and D.M. DeLong. 1971. An Introduction to The Study of Insects, Third Edition. Holt, Rinehart and Winston. New York. Both, C. and M.E. Visser. 2003. Density dependence, territoriality, and divisi bility of resources: From optimality models to population processes. The American Naturalist 161(2) : 326-337. Cordoba-Aguilar, A. 1994. Adult Survival and Movement in Males of the Damselfly Hetaerina cruentata (Odonata: Calopterydigdae). Florida Entomologist 77(2): 256264. Grether, G. F. and Switzer, P.V. 2000. Mechanisms for the formation and maintenance of traditional night roost aggregations in a territorial damselfly. Animal Behavior 60 : 569-579. Huffaker, C.B. and Gutierrez, A.P. 1999. Ecological Entomology, Second Edition. John Wiley and Sons, New York. Johnson, C. 1964. The Evolution of Territoriality in the Odonata. Evolution 18: 89-92. Mikami, O.K. et. al. 2004. A new hypothesis for sp ecies coexistence: male-m ale repulsion promotes coexistence of competing species. Population Ecology 46: 213-217. Nobel, G. K. 1939. The role of dominance in the life of birds. In Johnson, C. 1964. The Evolution of Territoriality in the Odonata. Evolution 18: 89-92. Romoser, W.S. and J.G. Stoffolano. 1998. The Sc ience of Entomology. McGraw Hill, Boston, MA. Wingfield, G. D. and D. Pain. 1992. The influence of river flow rates on the breeding behavior of Calopteryx damselflies. Journal of Animal Ecology 61: 283-289.