Abstract
Despite their role in providing ecosystem services, insects remain overlooked in conservation planning, and insect management approaches often lack a rigorous scientific basis. The endangered Ohlone tiger beetle (Cicindela ohlone) occurs in a 24-km2 area in Santa Cruz County, California. The once larger metapopulation now consists of subpopulations inhabiting five patches of coastal prairie where it depends on bare ground for mating, foraging, and oviposition. Human activities have eliminated natural disturbances and spread invasive grasses, reducing C. ohlone's bare-ground habitat. Management actions to restore critical beetle habitat consist of cattle and horse grazing, maintaining slow bicycle speeds on occupied public trails, and artificial creation of bare-ground plots. Recreational biking trails help maintain bare ground, but can cause beetle mortality if left unregulated. We tracked C. ohlone survivorship and estimated fecundity for three years. We then constructed a stage-structured population projection matrix model to estimate population viability among the five patches, and to evaluate the success of management interventions. We demonstrate that habitat creation, regulation of bicycle speed, and migration between patches increase C. ohlone survival and population viability. Our results can be directly applied to management actions for conservation outcomes that will reduce species extinction risk and promote recolonization of extirpated patches.
Highlights
The ultimate causes of species endangerment are most commonly habitat loss and invasive species introductions [1], proximate causes are reduced viability of small populations via genetic degeneration and demographic and environmental stochasticity [2,3,4]
We conducted this study from January 2010 to August 2012 within the five remaining populations of C. ohlone, located in different coastal terrace prairie sites within a 24 km2 area in Santa Cruz County, California: Lower Marshall (LM, 1.5 ha, 37.02uN 122.07uW) and Wilder Ranch (WR, 3.5 ha, 37.01uN 122.09uW), 1.3 km apart in the center of the range; Moore Creek
By averaging the three fecundity measurements described in the methods, we obtained the following fecundity (F) estimates for each population: GW 22.9 (66.51); LM 14.8 (65.81); WR 6.49 (63.08); Moore Creek (MC) 19.7 (64.17); UC 26.3 (63.49)
Summary
The ultimate causes of species endangerment are most commonly habitat loss and invasive species introductions [1], proximate causes are reduced viability of small populations via genetic degeneration and demographic and environmental stochasticity [2,3,4]. It is important to understand the effect of management actions on tangible population viability goals of endangered species to ensure efficient and effective use of resources to prevent species extinctions [4,9,10]. Despite their significance in ecosystem functions, insects are frequently overlooked in conservation actions, and endangered insect recovery plans often lack quantitative population goals to ensure long-term viability [11,12]. Tiger beetles are associated with distinct disturbance-dependent bare-ground habitats needed to forage, find mates, and oviposit; while they are sensitive to habitat degradation, they are increasingly dependent on anthropogenic disturbance [13,15]
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