Changes in the abundances, identities, and distributions of plants and phytoplankton will shift sites and quantities of primary production, and affect energy
transfer and species interactions across impacted ecosystems. For plants, these shifts
will be hindered or helped by their symbionts depending on the interaction. For
instance, by conferring tolerance to abiotic stresses, endophytes and MF may expand
their hosts’ ranges into warmer and more arid regions. And while nitrogen-fixing
bacteria and EcMF tend to invade new territories alongside their woody hosts, those
with AMF tend to form novel associations in introduced ranges (Nunez and Dickie
2014). Those plants relocating with symbionts in tow are likely to disrupt native
associations (Rodriguez-Echeverria 2010), which could have systemwide effects.
Also, microbe-mediated plant–soil feedbacks are among the most important determinants of soil carbon and nitrogen, yet also the least understood (Classen et al.
2015). Hence understanding plant microbiota is critical for predicting plant
responses to climate change, and associated climate feedback, but also for efforts
aimed at conserving plants (Carthey et al. 2020).
Failing symbioses often occupy niches that only symbiotic organisms can
occupy, so replacement will occur only if other symbiotic organisms are able to
move in, or over time, if new symbioses form. In terrestrial systems, the widespread
loss of sap-feeding insects would re-open this challenging niche for the first time in
tens of millions of years. However, since the majority of sap feeders are specialized
to particular plant groups, even those fortunate species carrying thermally stable
obligate symbionts would be unlikely to switch to vacated niches. This is because
the same genome degradation that hampers thermal tolerance also results in inflexible nutrient provisioning (Hansen and Moran 2014). The minority of
sap-feeding arthropods that are both food–plant generalists and harbor thermally
tolerant obligate symbionts may be able to broadly take advantage of this opportunity. However, this homogenized cohort of replacements would further diminish
associated communities as many natural enemies are also highly specialized.
In marine systems, the loss of hard corals creates opportunities for other
photosymbiotic organisms, such as soft corals and sponges, which show greater
tolerance to warm temperatures and acidification since most of the likely ecological
replacements are non-calcifying (Wee et al. 2019; Norstrom et al. 2009; Bell et al.
2013). Unfortunately, these potential replacements too often show limited resilience
to repeated bleaching events, and are predicted to reduce the diversity of supported
communities (Slattery et al. 2019; Cruz et al. 2015). Hence, these would likely be
short-term replacements that provide inferior ecosystem services.
Climate challenged microbial symbioses will also disrupt macro-symbioses.
Another group of Symbiodiniaceae-harboring anthozoans, the sea anemones engage
in macro-symbioses with a variety of fish and invertebrates, most notably clownfish,
providing protective services in exchange for nutritive excrement. As with other
photosymbiotic animals, anemones bleach when stressed resulting in smaller animals and reduced abundance. In turn, this decreases the fecundity and growth rates
of clownfish (Apprill 2020). Clownfish show preferences for unbleached anemones,
and may be able to behaviorally adjust, assuming healthy hosts remain available
(Scott and Dixson 2016). In terrestrial systems, the decline of sap-feeding insects
16 Symbiosis in a Rapidly Changing World
283
transfer and species interactions across impacted ecosystems. For plants, these shifts
will be hindered or helped by their symbionts depending on the interaction. For
instance, by conferring tolerance to abiotic stresses, endophytes and MF may expand
their hosts’ ranges into warmer and more arid regions. And while nitrogen-fixing
bacteria and EcMF tend to invade new territories alongside their woody hosts, those
with AMF tend to form novel associations in introduced ranges (Nunez and Dickie
2014). Those plants relocating with symbionts in tow are likely to disrupt native
associations (Rodriguez-Echeverria 2010), which could have systemwide effects.
Also, microbe-mediated plant–soil feedbacks are among the most important determinants of soil carbon and nitrogen, yet also the least understood (Classen et al.
2015). Hence understanding plant microbiota is critical for predicting plant
responses to climate change, and associated climate feedback, but also for efforts
aimed at conserving plants (Carthey et al. 2020).
Failing symbioses often occupy niches that only symbiotic organisms can
occupy, so replacement will occur only if other symbiotic organisms are able to
move in, or over time, if new symbioses form. In terrestrial systems, the widespread
loss of sap-feeding insects would re-open this challenging niche for the first time in
tens of millions of years. However, since the majority of sap feeders are specialized
to particular plant groups, even those fortunate species carrying thermally stable
obligate symbionts would be unlikely to switch to vacated niches. This is because
the same genome degradation that hampers thermal tolerance also results in inflexible nutrient provisioning (Hansen and Moran 2014). The minority of
sap-feeding arthropods that are both food–plant generalists and harbor thermally
tolerant obligate symbionts may be able to broadly take advantage of this opportunity. However, this homogenized cohort of replacements would further diminish
associated communities as many natural enemies are also highly specialized.
In marine systems, the loss of hard corals creates opportunities for other
photosymbiotic organisms, such as soft corals and sponges, which show greater
tolerance to warm temperatures and acidification since most of the likely ecological
replacements are non-calcifying (Wee et al. 2019; Norstrom et al. 2009; Bell et al.
2013). Unfortunately, these potential replacements too often show limited resilience
to repeated bleaching events, and are predicted to reduce the diversity of supported
communities (Slattery et al. 2019; Cruz et al. 2015). Hence, these would likely be
short-term replacements that provide inferior ecosystem services.
Climate challenged microbial symbioses will also disrupt macro-symbioses.
Another group of Symbiodiniaceae-harboring anthozoans, the sea anemones engage
in macro-symbioses with a variety of fish and invertebrates, most notably clownfish,
providing protective services in exchange for nutritive excrement. As with other
photosymbiotic animals, anemones bleach when stressed resulting in smaller animals and reduced abundance. In turn, this decreases the fecundity and growth rates
of clownfish (Apprill 2020). Clownfish show preferences for unbleached anemones,
and may be able to behaviorally adjust, assuming healthy hosts remain available
(Scott and Dixson 2016). In terrestrial systems, the decline of sap-feeding insects
16 Symbiosis in a Rapidly Changing World
283