620 A. Balestrieri et al.


TABLE 3 Modelling scenarios for assessing the viability of the otter population reintroduced on the River Ticino, with demographic input data for Vortex simulations.


Biological parameters Inbreeding depression


State variables


Reproductive system Age at first offspring


Max. age of reproduction Max. lifespan


Max. number of broods per year Max. number of progeny per year


Sex ratio at birth % breeding at low density


% breeding at carrying capacity % adult females breeding Reproductive rates


Age-specific mortality rates (%) 0–1 year 1–2 years 2–3 years .3 years


Number of types of catastrophes Frequency of catastrophic events (%)


Data values Scenario 1 default


default


Scenario 2 default


polygynous polygynous polygynous Kruuk (2006) 3 years 10 years 12 years 1 3


default 3 years


10 years 12 years 1 3


1:1 70 20


1:1 70 20


default


default 2 years


10 years 12 years 1 2


1:1 60 20


{70−[(70−20) × (N/K)2]×[N/(1 +N)]} default


default


8 (F), 14 (M) 10 (F), 5 (M) 16 (F), 16 (M) 8 (F), 10 (M) 10 (F), 4 (M) 12 (F), 12 (M) 8 (F), 6 (M) 3 (F), 2 (M) 12 (F), 12 (M) 1


3


Severity for reproduction and survival (%) 0.2–0.75 % of males .2 years old in breeding pool 70 Population size (N0)


Carrying capacity (K) Supplementation


Initial rate of increase λ


1 3


0.2–0.75 70


50


1 3


0.2–0.75 70


2F, 2 M 2 F, 2 M 2F, 2 M 3F, 3 M 3 F, 3 M 3F, 3 M 50


50


2F, 2 M 2 F, 2 M 2F, 2 M 1.14–1.2


1.07–1.13


used package for modelling reintroduced populations (Armstrong & Reynolds, 2012) and guiding conservation initiatives (Hamilton & Moller, 1995; Gaona et al., 1998). Vortex is an individual-based, stochastic model that applies Monte Carlo simulations to model the dynamics of popula- tions by stepping through a series of events that describe both deterministic and stochastic processes (Lacy, 1993). Simulations allow the probabilistic assessment of (1) pop- ulation size and genetic variation of extant populations, (2) extinction risk at specified intervals, and (3) mean time to extinction of those simulated populations that became extinct. Weretrieved biological parameters from the available lit-


erature (Table 3; Larsson & Ebenhard, 1994; Ansorge et al., 1997; Ebenhard, 2000; Hauer et al., 2002; Kruuk, 2006; Kuhn & Jacques, 2011), and assessed carrying capacity based on otter density in southern Italy (Prigioni et al.,


1.14–1.23


2006b). To account for the uncertainty about the number of otter pairs released and the possibility of unintentional supplementation by otters escaped from two enclosures in the 2–3 years following the start of the reintroduction pro- ject, we set the population size (N0) at three different values (1–3 pairs) for each scenario and simulated the adding of a pair of individuals per year at time t0 + 1 and t0 + 2 (Table 3). The risk of a catastrophe was set at 3%, assuming that excep- tional floods, which may occur at intervals of c. 30–35 years (Cattaneo et al., 2000), could primarily affect the survival of juveniles. For each scenario, we ran 500 simulations over a 100-year period, defining extinction as the point when one sex was eliminated. We conducted sensitivity tests for uncertain parameters,


to examine the effects of a range of values for each parameter on the probability of otter survival. We tested inbreeding depression, quantified as the number of lethal equivalents


Oryx, 2022, 56(4), 617–626 © The Author(s), 2021. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605321000107


1 F, 1 M 1 F, 1 M 1 F, 1 M Uncertainty on the number of reintroduced pairs


0.18–0.20 otters/km (Prigioni et al., 2006b)


1 F, 1 M 1 F, 1 M 1 F, 1 M Eventually escaped individuals (J. Conroy, in: Prigioni et al., 2009)


Scenario 3 default


Sources O’Grady et al. (2006)


Kuhn & Jacques (2011) Ansorge et al. (1997) Ebenhard (2000)


2.3–2.6 (Larsson & Ebenhard 1994; Hauer et al., 2002) Ansorge et al. (1997)


Ansorge et al. (1997), Hauer et al. (2002)


Normal distribution of the N of offspring per female per brood


24 (F), 34 (M) 52 (F), 52 (M) 17 (F), 17 (M) Ansorge et al. (1997), Larsson & Ebenhard (1994)


Exceptional flood October 2000 (Cattaneo et al., 2000)


Return period: 30–35 years (Cattaneo et al., 2000)


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