Life-history variation in a tropical cooperative bird: Ecological and social effects on productivity

2017-03-16T03:13:08Z (GMT) by Nataly Alexandra Hidalgo Aranzamendi
Reproduction and survival are two fundamental traits that define an individuals’ lifetime. Life-history variation within individuals can be related to individual differences on balancing  reproduction and survival against the constraints imposed by the physical and environmental conditions they experience. Since individuals vary widely within and between populations in respect to life-history traits, this variation transcends individuals, and life-history strategies differ between species. Understanding the selective pressures that affect individuals will offer an insight on what limits each species’ life-history strategy. Here I focus on the ecological and social forces that affect reproduction of the cooperative breeding purple-crowned fairy-wren <i>Malurus coronatus</i>, a tropical species that is located at the slow-life history end of the continuum. Using ten years of data from individual longitudinal stories, I analyse many aspects of reproduction: what are the environmental cues that trigger timing of breeding, how much do these environmental variables alone or in combination with social and other ecological conditions influence the final outcome of reproduction and what strategies do pairs use to minimise losses produced by external factors. I demonstrate that <i>Malurus coronatus</i> has a fine-tuned mechanism to time breeding cycles with rainfall and that rainfall also determines the quantitative output of successful nest attempts. <br> However, means and extremes of rainfall and temperature have different antagonistic effects that directly or indirectly decrease reproductive success, affecting reproductive success by flooding, increased predation, reduced egg hatchability or lower offspring survival. To overcome such losses,pairs should invest in nest defence and brood rearing, and I test whether this could be improved as a result of long-term partnerships. However, I found that retaining the same partner does not increase productivity. Motivated by this lack of benefits of staying together, I analysed if an adaptive response was to change partners (divorce) if opportunities are available. Divorce is driven by females taking breeding positions in higher quality territories, however this does not lead to immediate reproductive improvements. More generally, high quality territories (with more vegetation cover) are consistently identified as key factors associated with increased productivity by decreasing the likelihood of nest failure and recruiting more fledglings, which confirms previous research on this species and highlights the importance of “real estate”. All findings in <i>Malurus </i><i>coronatus</i> could possibly be commonplace in other tropical species that occupy year-round territories and are exposed to similar environmental selective pressures. These findings increase what is known for tropical species with a slow-life history strategy, data that is currently scarce. Moreover, my research highlights some potential threats of climate change, in which adaptive responses might not be enough to ameliorate negative impacts due to the slow-pace of reproduction in this species. The importance of habitat quality on reproductive success suggest that the preservation of healthy habitat would be crucial to guarantee this species survival.