"Conservation objective";"Benefits of connectivity";"Risks of connectivity";"General rules"
"Maintenance of genetic diversity";"• Reduces inbreeding depression • Increases selection opportunities for strongly beneficial alleles";"• Reduces diversification through neutral evolution (drift) • Reduces likelihood of novel alleles establishing for local adaptation (outbreeding depression)";"• Low rates of dispersal can still have important effects on genetic processes (Arenas et al. 2014 this book), so connectivity may be defined using lower migration thresholds than for other processes"
"Viability of populations";"• Can create metapopulations out of isolated populations, reducing stochastic extinction risk • Enables mobile individuals to escape from local disturbances • Facilitates range shifts in response to climate change";"• May reduce viability of metapopulations by collapsing them into simple populations, increasing stochastic extinction risk • May facilitate spread of endemic or epidemic diseases and predators";"• Benefits of connectivity are generally assumed to outweigh risks • Number of connections should be proportional to size of patches (Figure 1) • Connections that traverse broad-scale temperature gradients are important in the context of climate change (Settele et al. 2014) • Connections themselves may constitute important habitat and so effectively increase patch sizes (Klenke et al. 2014 this book)"
"Community diversity";"• Benefits for population viability (above), plus: • Facilitates arrival of new species, potentially increasing local (α) diversity.";"• Risks for population viability (above), plus: • May facilitate invasions by competitive species, decreasing overall (γ) diversity and threatening specialist species • Long-range connectivity may decrease among-site (β) diversity";"• For habitat-specialists, connections should be of comparable quality to core habitat • Edge (ecotone) habitats are crucial for many species • Solutions should consider the needs of taxa most prone to habitat fragmentation"
"Enhancing ecosystem functions and services";"• For any keystone species, see benefits for population viability (above) • Resilience may increase with local diversity (see benefits for community diversity, above)";"• For any keystone species, see risks for population viability (above) • Resilience may increase with among-site-diversity (see risk of long-range connectivity, above)";"• Should consider disservices (pest species/communities) as well as services • Connections can also serve as a distribution network for service provision linked to particular habitats (e.g. pollination, biocontrol, aesthetic services) (Steffan-Dewenter et al. 2014 this book)"
Overall;"• Incorporating community diversity with population viability, moderate connectivity has many benefits";"• Valuing neutral genetic diversity, or certain ecosystem functions, may entail more risks from connectivity";"• Often intermediate levels of connectivity perform best, but the optimum level will depend on the mobility of the species, the amount of area required to maintain viable populations, and the aspect of conservation concerned (Marsh et al. 2014 this book)"