Residence advantage in heterospecific territorial disputes of Erythrodiplax Brauer species (Odonata, Libellulidae)

Vantagem do residente nas disputas territoriais interespecíficas entre espécies de Erythrodiplax (Odonata, Libellulidae)

BIOLOGY, ECOLOGY AND DIVERSITY

Residence advantage in heterospecific territorial disputes of Erythrodiplax Brauer species (Odonata, Libellulidae)

Vantagem do residente nas disputas territoriais interespecíficas entre espécies de Erythrodiplax (Odonata, Libellulidae)

Daniela Chaves Resende

Laboratório de Bioinformática e Evolução, Departamento de Biologia Geral, Universidade Federal de Viçosa, 36570-000, Viçosa-MG, Brasil. [e-mail]

ABSTRACT

Residence advantage in heterospecific territorial disputes of Erythrodiplax Brauer species (Odonata, Libellulidae). Territories are the outcome of interactions determining where and how long individuals settle. To odonate species, aggressive disputes are not so common since the outcome can be predetermined by advantages such as residency, age, and body size. However, it is possible to predict that at heterospecific disputes, larger body-sized or more aggressive species have some profits overcoming these individual advantages, generating patterns of species hierarchy. Here, I studied the aggressiveness of five Erythrodiplax species (Odonata, Libellulidae) during territorial disputes and verified if larger body-sized species are more aggressive than smaller ones or if the residence advantage prevails on the heterospecific disputes. Larger species were not more aggressive than smaller ones and winners of intra- and interspecific territorial disputes were defined mainly by the residence. So, the residence advantage between heterospecific opponents appears to prevail over any other asymmetry among these species. This pattern may occur because, despite the territorial behaviour in dragonfly males, heterospecific disputes may not increment male reproductive success because it may not increase their access to females.

Keywords: Asymmetry; hierarchy; interspecific competition; territoriality.

RESUMO

Territórios resultam de interações comportamentais que determinam onde e por quanto tempo um indivíduo consegue se estabelecer. Para espécies de Odonata, as disputas agressivas entre machos são raras, pois, vantagens pré-existentes como idade, tamanho corporal ou residência definem o vencedor. Entretanto, é possível esperar que nas interações interespecíficas, espécies de maior tamanho corporal ou mais agressivas possam ter vantagens nas disputas, sobrepujando as vantagens individuais pré-existentes e gerando um padrão hierárquico entre as espécies. Neste trabalho, eu estudei a agressividade exibida por espécies de Erythrodiplax (Odonata, Libellulidae) e verifiquei se espécies maiores são mais agressivas ou se a vantagem do residente prevalece também nas disputas interespecíficas. Espécies maiores não são mais agressivas e os vencedores das disputas territoriais intra- e inter-específicas foram machos residentes. Logo, a vantagem do residente parece prevalecer sobre qualquer assimetria existente entre as espécies estudadas, o que pode ocorrer porque, apesar do comportamento territorial exibido por elas, o recurso defendido pelos machos é o acesso às fêmeas e vencer disputas interespecíficas pode não afetar positivamente o sucesso reprodutivo dos mesmos.

Palavras-chave: Assimetria; competição inter-específica; hierarquia; territorialidade.

Territories are not fixed areas, but the outcome of complex behavioural interactions determining where and how long individuals settle (Gordon 1997). Territorial disputes among odonate males comprise behaviours or conventions that determine some kind of asymmetry between opponents, such as body size differences (Marden & Cobb 2004), previous experiences (Hsu et al. 2006) or simply residence (Waage 1988; Kemp & Wiklund 2004). The residence status appears to be an important source of asymmetry between opponents and frequently residents win territorial disputes (Alcock 1982; Van Buskirk 1986; Alcock 1987; Waage 1988). Intense disputes between intruders and residents are expected only if the intruder is strong enough to overcome the residence advantage or when both individuals consider themselves territorial residents (Waage 1988).

Odonate females do not present any form of parental care (Corbet 1962, 1999), so choice of a suitable oviposition site may be determinant to their reproductive success (Michiels & Dhondt 1990; Fincke 1992; Osborn & Samways 1996), mainly because odonate larvae present morphological and behavioural specializations that increase their survival in some specific microhabitats (Pritchard & Kortello 1997; Mikolajewski & Johansson 2003; McCauley 2007). In consequence, males defending territories with this suitable microhabitat must access more females, also increasing their reproductive success.

Costs associated to species co-occurrence into territorial sites may derive from (Singer 1990; Tynkkinen et al. 2004): i) heterospecific aggressiveness, ii) heterospecific mates or yet iii) female guard against heterospecific males, when the oviposition site is near to the territory. It is also possible that heterospecific competition for resources occurs during the larval phase (Johnson & Crowley 1980). So, it is reasonable to propose a selection of heterospecific aggressiveness mainly among related species sharing an ecological space, due to their high morphological similarities.

Territorial activity of odonate males can be affected by thermoregulatory abilities (De Marco & Resende 2002), since disputes involve rapid flies with intense muscle activity, increasing the thoracic temperature (May 1977; Marden 1989). Small sized species have a high convection heating, depending strongly from environmental temperature to be active, while larger species may be more able to control body temperature by exposition to solar radiation (May 1991). If body size affects thermoregulatory abilities of species, it may also affect male activity patterns (May 1991; De Marco & Resende 2002). Indeed, competitive asymmetry is often associated with individual size differences (Aikio 2004). Larger species may be more aggressive than smaller ones due to their thermoregulatory abilities and fight advantages, so we could expect some pattern of hierarchy on the spatial distribution or on resource utilization.

Erythrodiplax Brauer, 1868 is highly diversified tropical Libellulidae (Odonata) genus, comprising about 58 species (International Dragonfly Fund 2003). In general, males of Erythrodiplax fusca (Rambur, 1842), E. famula (Erichson, 1848), E. latimaculata Ris, 1911, E. pallida (Needham, 1904) and E. media Borror, 1942 defend mating territories around lakes or river shorelines and swamps. Males of these species perch on branches, grasses, macrophytes or directly on the soil and the females lay their eggs after soon copulation, directly on water with some kind of submerged vegetation, along the shoreline of the pond (De Marco et al. 2005; Resende & De Marco 2008).

In this paper, I studied the aggressiveness exhibited by five Erythrodiplax species (Libellulidae, Odonata): E. fusca, E. famula, E. latimaculata, E. pallida and E. media, during territorial disputes. I emphasized heterospecific interactions, verifying if larger body-sized species are more aggressive than smaller ones, and if the residence advantage prevail on heterospecific disputes.

MATERIAL AND METHODS

The behavioral observations were made in the Área de Proteção Ambiental (APA) São José, Minas Gerais, Brazil (21º07'00"S and 44º12'10"W). The climate presents a dry season from April to September and a rainy season in the summer. Mean annual temperature is about 19ºC with maximum between 21ºC and 22ºC. The APA (4758 ha) comprises a contact zone between Cerrado and Semidecidual Seasonal Atlantic Forest. Water courses are abundant mostly with perennial drainages.

I conducted this study between January and March, period of year with the highest abundances of dragonflies (De Marco & Latini 1998). I observed individual behaviour between 9:00 and 14:00 h to control effects of luminosity and humidity (Heinrich & Casey 1978; May 1979). I sampled four similar swamps with different altitudes, and all of them were disturbed areas, where originally there was Cerrado and Galery Forest.

Territorial Behaviour

The sampling unit for behavioural observations was the sequence of behaviours registered during one minute of focal observation of an individual (Altmann 1974). The moment of each behaviour start was noted, allowing the estimation of time spent in each activity. Individuals were selected at different locations of the swamps to avoid pseudoreplication (repeated observations of the same individual). I observed 54 males for E. fusca, 24 for E. famula, 65 for E. latimaculata, 44 for E. media and 45 for E. pallida.

I classified behavioural activities following De Marco (1998), such as: i) perch: including all classes of perch; ii) patrolling: flying back and forward through an area; iii) transition flight: passing through an area without patrolling and iv) territorial defence (agonistic interaction): chasing another individual. I distinguished the territorial defence between conspecific (intraspecific dispute) and heterospecific (heterospecific dispute) males. The territorial disputes were considered only when I was able to determine the resident male and the winner (males that remained in the territory at the end of disputes). I used a Chi-square analysis to test differences on ability of males to win disputes among different species and between residents and intruders.

Body Size

Five individuals of each species were collected and dried at 40ºC. Differences among mean weight of species were tested using a single classification analysis of variance. To test the hypothesis that larger species are more aggressive, I used a Linear Regression comparing mean proportion time spent on aggressive behaviour (patrol and territorial disputes) and mean dry weight for these species. Despite the obvious common ancestry shared by these species, I could not use a comparative analysis to test this hypothesis because there is no a phylogeny proposed to this group.

RESULTS

Males of Erythrodiplax species exhibited similar territorial defence behaviour and the five species spent most of their time perched (Fig. 1), spending little time in aggressive behaviour. E. famula, E. media and E. fusca males spent more time in territorial disputes and patrol than E. latimaculata and E. pallida (Table I), but, all species spent little time in heterospecific territorial disputes (Table I), so differences on aggressive behaviour among these species are mainly due to intraspecific aggressiveness.

There are significant differences in body weight among species (F = 5.05; d.f. = 4, 22; P < 0.01). E. famula and E. fusca are larger than the other Erythrodiplax species, presenting similar body size (Fig. 2). E. latimaculata, E. media and E. pallida present similar body size, but, the last species presented the smaller individuals (Fig. 2). Despite these differences, the mean weight does not explain the time spent in patrol and territorial disputes for Erythrodiplax species (N = 5; t = 1.25; P = 0.29; R² = 0.35). Males of all species won or lost heterospecific disputes at the same frequency (χ² =8.6; d.f.=7; P=0.28; Table II). Territorial owners won heterospecific territorial disputes more frequently than intruders (Table III) and there are no differences in this pattern between the five species (χ²=3.3; d.f.=4, P=0.50). Similarly, the resident Erythrodiplax males won intraspecific territorial disputes more frequently than intruders (Table III) and this effect was similar between the studied species (χ²=6.06; d.f.=4; P=0.19).

DISCUSSION

An intruder would exclude a resident from its territory only if it had a higher territory defender's quality [Resource Holding Power - RHP (Parker 1974)] (Alonzo 2004; Lindström & Pampoulie 2004), but, this event looks like rare. This pattern may occurs: i) when resource is concentrated and throughout constant disputes, individuals with highest quality occupied territories with more resources (Kemp & Wiklund 2004; Koskimäki et al. 2004); ii) when territory property increases individual quality, for example, due to more food availability (Metcalfe et al. 2003) or, iii) when costs from territorial disputes are different to intruder and resident (Parker 1974).

For Odonata species, the territory defender's quality is frequently correlated to differences in body size. Larger males present frequently a higher lifetime mating success for diverse Libellulidae species, like Sympetrum rubicundulum (Say, 1839) (Van Buskirk 1987), Plathemis lydia (Drury, 1773) (Marden 1989), Libellula luctuosa Burmeister, 1839 (Moore 1996) and Orthetrum chrysostigma (Uhler, 1858) (Miller 1983). Moreover, this effect of body size on lifetime mating success means highly connected to territoriality (Sokolovska et al. 2000). In fact, space or resource competition is clearly related to population dynamics, so, aggressiveness should vary in function of body size (Parr 1983; Marden & Cobb 2004; Koskimäki et al. 2004).

However, in this study, in both intra- and heterospecific territorial disputes, the residents frequently won and maintained their territories. So, the individual residence prevails on heterospecific disputes, despite any morphological or behavioural differences and despite any competitive asymmetry among the species. Heterospecific aggressiveness may result from a complex interactions of asymmetries depending of kind of resources are limited (Aikio 2004) and body size prevalence must be replaced by residence like determinant source of asymmetry. Competitive asymmetry among species results from a trade-off between the territory size and the ability to compete for resources into the overlapping area (Aikio 2004). Individuals of larger territories will have larger overlapping areas, spending more energy to establish and to maintain their territories, what may decrease their ability to compete for resources and this trade-off may allow the coexistence of species with competitive asymmetries (Aikio 2004).

Dragonfly males dispute for territories with perches and/or oviposition substrates, aiming as final objective the mate acquisition and this cannot compensate heterospecific aggressiveness. Even if males of odonate larger species had enough advantages to exclude males of smaller species from their territories, the spent of energy in these disputes must not increase individual mating success because the final resource – females - is not disputed. Despite any costs associated to species co-occurrence, heterospecific aggressiveness may not evolve mainly because males are able to use visual cues to distinguish between hetero- and conspecific males (Schultz & Switzer 2001; Tynkkinen et al. 2004).

So, the low heterospecific aggressiveness of studied Erythrodiplax species must derive from the residence advantage between opponents, particularly, because in a system with mating territorial defence, intraspecific competition must be so more intense, that coexistence among similar species must be allowed, just as the classic Lotka-Volterra competition model predicted.

Acknowledgments. I thank to Fernando Silveira, Paulo De Marco Jr. and Anderson Latini for numerous discussions and to Daniel Resende for the field assistance. This study was financially supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), the US Fish and Wildlife Service and the Ramsar Convention on Wetlands.

Received 19/03/2009; accepted 30/12/2009

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Publication Dates

• Publication in this collection
  07 May 2010
• Date of issue
  Mar 2010

History

• Accepted
  30 Dec 2009
• Received
  19 Mar 2009