Schnell, Jessica K.
Function of vocalization length and warble repertoire size in orange-fronted conures
2017-12, Balsby, Thorsten J. S., Eldermire, Erin R. B., Schnell, Jessica K., Poesel, Angelika, Walsh, Rachel E., Bradbury, Jack W.
Bird vocalizations consist of songs and calls. The calls tend either to be given singly or to consist of multiple elements given in a rapid string. The multi-element bird calls of some nonpasserines resemble passerine song and can contain many diverse elements. Multi-element vocalizations can change the signal message by varying the number of elements and/or the diversity and selection of element types. The use of multi-element variation has been extensively studied in passerine songs, but only rarely in nonpasserines. Here we examined two multi-element vocalization types in a wild parrot, the orange-fronted conure, Eupsittula canicularis: ‘warbles’ consist of diverse elements (heterotypic) whereas ‘peaches’ consist of repetitions of the same element (homotypic). Both call types are used in aggressive interactions between pairs or flocks. We used playbacks to wild conure flocks in Costa Rica to determine whether the number of elements (both types) and/or the diversity of elements (warble repertoire size) produced differentiable responses. Both short and long peach call series usually elicited retreat, but longer series led to reduced warbling and increased soft contact calls (zip calls) when responses were compared with those of short series. The warble stimuli mainly affected the approach behaviour leaving most call rates unaffected: more flocks left the area in response to long warbles with large repertoires, whereas short, small repertoire stimuli resulted in a closer approach. Both experiments showed that the length of both types of multi-element call and element diversity in warbles are salient to the wild conures. The results suggest that longer series of both call types and higher diversity warbles may be perceived by the birds as more aggressive, leading to the observed patterns of approach, retreat and interaction. The results suggest that vocal complexity in parrots has a signal value similar to that found in passerines.
Estimating extinction risk with metapopulation models of large-scale fragmentation
2013-06, Schnell, Jessica K., Harris, Grant M., Pimm, Stuart L., Russell, Gareth J.
Habitat loss is the principal threat to species. How much habitat remains-and how quickly it is shrinking-are implicitly included in the way the International Union for Conservation of Nature determines a species' risk of extinction. Many endangered species have habitats that are also fragmented to different extents. Thus, ideally, fragmentation should be quantified in a standard way in risk assessments. Although mapping fragmentation from satellite imagery is easy, efficient techniques for relating maps of remaining habitat to extinction risk are few. Purely spatial metrics from landscape ecology are hard to interpret and do not address extinction directly. Spatially explicit metapopulation models link fragmentation to extinction risk, but standard models work only at small scales. Counterintuitively, these models predict that a species in a large, contiguous habitat will fare worse than one in 2 tiny patches. This occurs because although the species in the large, contiguous habitat has a low probability of extinction, recolonization cannot occur if there are no other patches to provide colonists for a rescue effect. For 4 ecologically comparable bird species of the North Central American highland forests, we devised metapopulation models with area-weighted self-colonization terms; this reflected repopulation of a patch from a remnant of individuals that survived an adverse event. Use of this term gives extra weight to a patch in its own rescue effect. Species assigned least risk status were comparable in long-term extinction risk with those ranked as threatened. This finding suggests that fragmentation has had a substantial negative effect on them that is not accounted for in their Red List category.
How individual links affect network stability in a large-scale, heterogeneous metacommunity
2016, Brodie, Jedediah F., Mohd-Azlan, Jayasilan, Schnell, Jessica K.
Elucidating how dispersal and landscape connectivity influence metacommunity stability will shed light on natural processes structuring ecosystems and help prioritize conservation actions in an increasingly fragmented world. Much of the theoretical and mathematical development of the metacommunity concept has been based on simplified experimental systems or simulated data. We still have limited understanding of how variation in the habitat matrix and species-specific differences in dispersal ability contribute to metacommunity dynamics in heterogeneous landscapes. We model a metacommunity of rainforest mammals in Borneo, a tropical biodiversity hotspot, where protected areas are increasingly isolated by ongoing habitat disturbance and loss. We employ a combination of hierarchical models of local abundance, circuit-theory-based dispersal analysis, and metapopulation models. Our goal was to understand which landscape links were the most important to metapopulation persistence and metacommunity stability. Links were particularly important if they were short and connected two large patches. This was partly because only the very shortest links could be traversed by poorly dispersing species, including small herbivores such as chevrotains (Tragulus spp.) and porcupines. Links that join large patches into a “super-patch” may also promote island–mainland rather than Levins-type metapopulation dynamics for good dispersers, particularly large carnivores such as clouded leopards (Neofelis diardi) and sun bears (Helarctos malayanus), reducing metapopulation extinction risk and thereby enhancing metacommunity stability. Link importance to metacommunity stability was highly correlated between heterogeneous and homogeneous landscapes. But link importance to metapopulation capacity varied strongly across species, and the correlation between heterogeneous and homogeneous landscape matrix scenarios was low for poorly dispersing taxa. This suggests that the environmental conditions in the area between habitat patches, the landscape matrix, is important for assessing certain individual species but less so for understanding the stability of the entire metacommunity.
Quantitative Analysis of Forest Fragmentation in the Atlantic Forest Reveals More Threatened Bird Species than the Current Red List
2013, Schnell, Jessica K., Harris, Grant M., Pimm, Stuart L., Russell, Gareth J.
Habitat loss and attendant fragmentation threaten the existence of many species. Conserving these species requires a straightforward and objective method that quantifies how these factors affect their survival. Therefore, we compared a variety of metrics that assess habitat fragmentation in bird ranges, using the geographical ranges of 127 forest endemic passerine birds inhabiting the Atlantic Forest of Brazil. A common, non-biological metric — cumulative area of size-ranked fragments within a species range — was misleading, as the least threatened species had the most habitat fragmentation. Instead, we recommend a modified version of metapopulation capacity. The metric links detailed spatial information on fragment sizes and spatial configuration to the birds’ abilities to occupy and disperse across large areas (100,000+ km2). In the Atlantic Forest, metapopulation capacities were largely bimodal, in that most species’ ranges had either low capacity (high risk of extinction) or high capacity (very small risk of extinction). This pattern persisted within taxonomically and ecologically homogenous groups, indicating that it is driven by fragmentation patterns and not differences in species ecology. Worryingly, we found IUCN considers some 28 of 58 species in the low metapopulation capacity cluster to not be threatened. We propose that assessing the effect of fragmentation will separate species more clearly into distinct risk categories than does a simple assessment of remaining habitat.
Metapopulation Capacity Meets Evolutionary Distinctness : Spatial Fragmentation Complements Phylogenetic Rarity in Prioritization
2016, Schnell, Jessica K., Safi, Kamran
Many species have declined or already gone extinct due to the human activities across the world causing what is termed the current sixth mass extinction event. The biggest determinant of species survival is the availability of a network of suitable habitat, affecting population size and eventual extinction risk. Considering that modern technology allows us to efficiently quantify habitat loss, species distribution data can inform us of the required minimum connectivity of habitats. Evolutionary distinctiveness (ED) is already part of conservation schemes to prioritize rare traits and unique phylogenetic history. However, so far none of these prioritisations quantifies the spatial constraints of a species to estimate long-term persistence based on the fragmentation of the landscape. Metapopulation capacity (λM) is one such measurement for quantifying fragmentation. Here we propose a combination of metapopulation capacity and phylogenetic distinctiveness to prioritize important specific habitat patches for evolutionary distinct species. We applied the new framework to prioritize island mammals and found Data Deficient and Least Concern species with a high combined value in ED and λM. Balancing between the extinction risks of solitary islands and the potential loss of unique evolutionary history of rare species on these islands can be a worthwhile exercise in prioritization schemes.