invasion ecology of high-altitude lakes. The reasons why some lakes show stronger
or weaker resistance to fish invaders are still largely speculative or need to be
studied in more detail. Indeed understanding the characteristics of the lakes which
determine a higher resistance to fish predation and resulting indirect ecological
impacts can help high-altitude lakes conservation and management and buffer such
a widespread conservation problem. It is generally accepted that ecological complexity and the existence of antipredatory refugia (e.g. aquatic vegetation and the
dark refugia in the deeper parts of deep lakes) enhance the resistance of native
aquatic communities (Knapp et al. 2001b; Pope et al. 2009). However little is
known about many aspects related to:
• The biology of introduced populations: the impact of different trout species has
not been compared in detail as well as the dependence between the fish density
and the magnitude of the impact.
• The ecology of invaded populations: the existence of metapopulations and the
vicinity to fishless lakes could probably contrast the effects of fish predation on
many prey species through immigration of new individuals, but, except for
amphibians (Vredenburg 2004), this issue has rarely been studied. Also, the egg
banks and propagules could subsidise native populations with new individuals
and buffer fish predation, but also, in this case, their roles have not been well
studied (but see Parker et al. 1996 and Latta et al. 2010). There are also many
overlooked aspects concerning the cascading effects of fish introduction (e.g.
trophic cascades) and their influence on the ecological connection between
invaded lakes and terrestrial habitats (reciprocal terrestrial and aquatic subsidies).
• The role of different fish management practices: the consequences of different
fish management practices (fishing bans vs. fishing enabled, periodic fish
stocking vs. fish stocking halt) on the magnitude of the ecological impact has
not been assessed.
• The evolutionary consequences of fish invasion: introduced species can produce
evolutive changes in natives, and the evolutionary component of
native/non-native species interactions are likely to be a cutting edge field of
research in invasion ecology, with important conservation consequences
(Lambrinos 2004; Schoener 2011).
• The interacting threats: the effects of fish can be exacerbated by interaction with
other stressors. Airborne pesticides (Davidson and Knapp 2007), infections by
moulds (chytridiomycosis; Walker et al. 2010; Rosa et al. 2013; Martel et al.
2013; Vredenburg et al. 2010) and viruses (Price et al. 2014; Teacher 2010),
climate changes (Bosch et al. 2007) or increased ultraviolet radiation by ozone
layer thinning (Adams et al. 2005), water exploitation and water-level fluctuations, point source of organic pollutants, can interact with introduced fish possibly
exacerbating the poor conservation status and the resilience potential of many
high altitude lakes at a local and regional scale. For example maintaining fishless
lakes or eradicating fish can be considered as a measure to contrast the biodiversity loss due to climate warming, restoring a safe stepping stone habitat for
many aquatic organisms forced to find cooler condition with an altitudinal shift.
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M. Ventura et al.
or weaker resistance to fish invaders are still largely speculative or need to be
studied in more detail. Indeed understanding the characteristics of the lakes which
determine a higher resistance to fish predation and resulting indirect ecological
impacts can help high-altitude lakes conservation and management and buffer such
a widespread conservation problem. It is generally accepted that ecological complexity and the existence of antipredatory refugia (e.g. aquatic vegetation and the
dark refugia in the deeper parts of deep lakes) enhance the resistance of native
aquatic communities (Knapp et al. 2001b; Pope et al. 2009). However little is
known about many aspects related to:
• The biology of introduced populations: the impact of different trout species has
not been compared in detail as well as the dependence between the fish density
and the magnitude of the impact.
• The ecology of invaded populations: the existence of metapopulations and the
vicinity to fishless lakes could probably contrast the effects of fish predation on
many prey species through immigration of new individuals, but, except for
amphibians (Vredenburg 2004), this issue has rarely been studied. Also, the egg
banks and propagules could subsidise native populations with new individuals
and buffer fish predation, but also, in this case, their roles have not been well
studied (but see Parker et al. 1996 and Latta et al. 2010). There are also many
overlooked aspects concerning the cascading effects of fish introduction (e.g.
trophic cascades) and their influence on the ecological connection between
invaded lakes and terrestrial habitats (reciprocal terrestrial and aquatic subsidies).
• The role of different fish management practices: the consequences of different
fish management practices (fishing bans vs. fishing enabled, periodic fish
stocking vs. fish stocking halt) on the magnitude of the ecological impact has
not been assessed.
• The evolutionary consequences of fish invasion: introduced species can produce
evolutive changes in natives, and the evolutionary component of
native/non-native species interactions are likely to be a cutting edge field of
research in invasion ecology, with important conservation consequences
(Lambrinos 2004; Schoener 2011).
• The interacting threats: the effects of fish can be exacerbated by interaction with
other stressors. Airborne pesticides (Davidson and Knapp 2007), infections by
moulds (chytridiomycosis; Walker et al. 2010; Rosa et al. 2013; Martel et al.
2013; Vredenburg et al. 2010) and viruses (Price et al. 2014; Teacher 2010),
climate changes (Bosch et al. 2007) or increased ultraviolet radiation by ozone
layer thinning (Adams et al. 2005), water exploitation and water-level fluctuations, point source of organic pollutants, can interact with introduced fish possibly
exacerbating the poor conservation status and the resilience potential of many
high altitude lakes at a local and regional scale. For example maintaining fishless
lakes or eradicating fish can be considered as a measure to contrast the biodiversity loss due to climate warming, restoring a safe stepping stone habitat for
many aquatic organisms forced to find cooler condition with an altitudinal shift.
192
M. Ventura et al.