Browsing by Author "Martin, Kathy"

Now showing 1 - 4 of 4
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    Complex dynamics of tree cavities and nest webs in the Americas
    (2018) Cockle, Kristina; Ibarra Eliessetch, José Tomás; Trzcinski, Kurtis; Wiebe, Karen L.; Altamirano Oyarzún, Tomás Alberto; Edworthy, Amanda; Martin, Kathy
    The Nest Web concept represents tree-cavity-nesting communities as hierarchical, commensal networks, whereby nesting cavities flow upward from trees to cavity producers (e.g., woodpeckers, decay organisms) to a diverse assemblage of non-excavators (e.g., parrots, songbirds). These nest webs are dynamic, complex, and often resilient. They include non-hierarchical feedback loops, such as facultative excavation, inter-guild predation and competition. For >20 years we studied >4000 nesting cavities in temperate British Columbia, Canada (1995-2016), temperate Chile (2010-2018) and subtropical Argentina (2006-2018), to examine the dynamics of cavity-nesting communities over time, at scales from individual cavities to whole nest webs. Individual cavities in large old-growth trees persisted longest. Cavities became larger as they aged, and were occupied by a succession of vertebrates (excavators, then small-bodied non-excavators, and finally largebodied non-excavators). Cavities produced 0–43 fledglings/cavity over their lifetime, but cavities with higher nest success were occupied fewer times by fewer species. At the nest web scale in Canada, an abundant facultative excavator declined in importance in the Nest Web during an insect outbreak that attracted obligate excavators, but then dramatically increased cavity production following wildfires. Logging resulted in disproportional biodiversity losses when it targeted key network hubs (large trees; Chile, Argentina) but not when a critical nesting tree species was retained (Canada). A nest web approach helped us understand interspecific interactions and test network theory; because these networks are strongly influenced by outside sources of uncertainty and non-linearity, a Complex Systems Science approach may improve predictions about their long-term dynamics
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    Fire regimes shape biodiversity: responses of avian guilds to burned forests in Andean temperate ecosystems of southern Chile
    (RESILIENCE ALLIANCE, 2021) Novoa Galaz, Fernando Javier; Altamirano Oyarzún, Tomás Alberto; Bonacic Salas, Cristian; Martin, Kathy; Ibarra Eliessetch, José Tomás
    Fire regimes of forests, i.e., time interval, frequency, extent, and severity of fire events, influence structural changes in the vegetation, and thus shape the composition of avian communities. We studied the diversity of avian guilds in sites with different fire regimes (unburned, burned 2002, burned 2015, and burned 2002 and 2015), testing both the "intermediate disturbance" and "vertical vegetation structure" hypotheses, in globally threatened temperate forests in Chile. From 2016 to 2018, we quantified habitat attributes (160 plots) and estimated avian richness and density (160 point counts). The site that was burned once in 2015 showed the highest density of standing dead trees at 96.5% higher than the unburned/control site, whereas the site that burned twice showed the lowest density of live trees, lowest average diameter at breast height of trees (DBH), and smallest volume of coarse woody debris. Overall, we recorded 35 avian species with the highest richness (n = 24 species) in the site that was burned once in 2002. We found that, 16 years after a site was burned, the avian community composition became relatively similar to the unburned site. The density of most avian guilds decreased in burned sites but granivores, shrub users, and migrants showed positive responses. Understory users, foliage users, and resident species showed negative responses to burned sites. These responses were strongly related to fire-driven changes in habitat attributes, supporting both of our tested hypotheses. Given that increasing levels of disturbance from fire are anticipated, future management of temperate forest biodiversity should consider that specific species and guilds will depend on remnant habitat attributes in burned sites.
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    Habitat-specialist owls, but not generalists, are reliable surrogates for taxonomic and functional diversity in Andean temperate forests
    (2015) Ibarra Eliessetch, José Tomás; Martin, Kathy
    Conservation practices commonly focus on measures of species diversity that merelyinclude information on species richness (i.e., taxonomic diversity). However, functionaldiversity (range, distribution and density of trait values of species in a community) should be more informative than taxonomic diversity as it measures those aspects of diversity thataffect ecosystem function. Previous work in the northern hemisphere has shown that owlsmay act as surrogates for taxonomic diversity but little is known on their value assurrogates of functional diversity. We assessed the surrogacy reliability of two sympatricowls, Strix rufipes (habitat-specialist) and Glaucidium nana (habitat-generalist), in Andeantemperate forests of southern Chile. During 2011-2013, we conducted 1,145 owl surveys,505 avian point-transects and 505 vegetation surveys across 101 sites comprising a range ofconditions from degraded habitat to structurally complex old-growth forest stands. Wefound that only Strix rufipes was a reliable surrogate for both taxonomic and functionaldiversity measures, including the density of vulnerable avian guilds (e.g., bamboounderstory users and large-tree users) and the degree of habitat-specialization of the aviancommunity. We found that forest-stand structural complexity (sites with dense understoryand availability of large trees) was the underlying mechanism driving the positive relation between forest-specialist owls and biodiversity. Our results show a tight association between habitat-specialist owls and avian functional traits that may be more informativethan species richness to prioritize the conservation of stable, functioning ecosystems
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    ¿No hay búhos en este sitio, o no los detectamos?: factores que influencian la detectabilidad de rapaces nocturnas en el bosque templado sudamericano
    (2013) Ibarra Eliessetch, José Tomás; Martin, Kathy; Altamirano, Tomás A.; Vargas, F. Hernán; Vermehren, Alejandra; Bonacic Salas, Cristian
    Los búhos son crípticos, de hábitos principalmente nocturnos y se encuentran en densidades bajas. Estudios sobre su ecología son susceptibles de incurrir en "falsos-ausentes" (i.e. no detección en sitios que en realidad sí están ocupados) y obtener estimadores sesgados de sus distribuciones y abundancias. Entre 2011 y 2013 evaluamos factores temporales, ambientales y biológicos que influencian las probabilidades de detección de Strix rufipes y Glaucidium nana en 101 sitios del bosque templado andino de Chile. Realizamos 1.145 muestreos mediante señuelos acústicos durante siete meses (dos temporadas reproductivas), obteniendo 292 detecciones para Strix y 334 para Glaucidium. Modelos de ocupación dinámicos para poblaciones abiertas indicaron probabilidades iniciales de 0,63 de ocupación y de 0,43 de detección para Strix, y de 0,78 y 0,36 para Glaucidium. Los mejores modelos indicaron que la probabilidad de detección de Strix es función de la luminosidad lunar (efecto positivo), ruido ambiental (negativo) y la detección de Glaucidium en el mismo sitio (positivo). Por su parte, la detectabilidad de Glaucidium fue función de la detección de Strix en el mismo sitio (efecto positivo), luminosidad lunar (positivo), ruido ambiental (negativo) y del período de muestreo en la temporada (mayores registros al final de estación reproductiva). La baja detectabilidad (<0,5) de ambas especies sugiere la necesidad de corregir el sesgo de detección en muestreos y programas de monitoreo, con el fin de asignar eficientemente los recursos (humanos y económicos) y obtener estimadores confiables sobre la distribución, abundancia y uso de hábitat de rapaces nocturnas del bosque templado sudamericano